Adding upstream version 1.16.10.upstream/1.16.10upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

31 files changed, 7576 insertions, 0 deletions

diff --git a/src/testing/allocs.go b/src/testing/allocs.go
new file mode 100644
index 0000000..1eeb2d4
--- /dev/null
+++ b/src/testing/allocs.go
@@ -0,0 +1,45 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testing
+
+import (
+	"runtime"
+)
+
+// AllocsPerRun returns the average number of allocations during calls to f.
+// Although the return value has type float64, it will always be an integral value.
+//
+// To compute the number of allocations, the function will first be run once as
+// a warm-up. The average number of allocations over the specified number of
+// runs will then be measured and returned.
+//
+// AllocsPerRun sets GOMAXPROCS to 1 during its measurement and will restore
+// it before returning.
+func AllocsPerRun(runs int, f func()) (avg float64) {
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
+
+	// Warm up the function
+	f()
+
+	// Measure the starting statistics
+	var memstats runtime.MemStats
+	runtime.ReadMemStats(&memstats)
+	mallocs := 0 - memstats.Mallocs
+
+	// Run the function the specified number of times
+	for i := 0; i < runs; i++ {
+		f()
+	}
+
+	// Read the final statistics
+	runtime.ReadMemStats(&memstats)
+	mallocs += memstats.Mallocs
+
+	// Average the mallocs over the runs (not counting the warm-up).
+	// We are forced to return a float64 because the API is silly, but do
+	// the division as integers so we can ask if AllocsPerRun()==1
+	// instead of AllocsPerRun()<2.
+	return float64(mallocs / uint64(runs))
+}
diff --git a/src/testing/allocs_test.go b/src/testing/allocs_test.go
new file mode 100644
index 0000000..5b346aa
--- /dev/null
+++ b/src/testing/allocs_test.go
@@ -0,0 +1,29 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testing_test
+
+import "testing"
+
+var global interface{}
+
+var allocsPerRunTests = []struct {
+	name   string
+	fn     func()
+	allocs float64
+}{
+	{"alloc *byte", func() { global = new(*byte) }, 1},
+	{"alloc complex128", func() { global = new(complex128) }, 1},
+	{"alloc float64", func() { global = new(float64) }, 1},
+	{"alloc int32", func() { global = new(int32) }, 1},
+	{"alloc byte", func() { global = new(byte) }, 1},
+}
+
+func TestAllocsPerRun(t *testing.T) {
+	for _, tt := range allocsPerRunTests {
+		if allocs := testing.AllocsPerRun(100, tt.fn); allocs != tt.allocs {
+			t.Errorf("AllocsPerRun(100, %s) = %v, want %v", tt.name, allocs, tt.allocs)
+		}
+	}
+}
diff --git a/src/testing/benchmark.go b/src/testing/benchmark.go
new file mode 100644
index 0000000..a8f75e9
--- /dev/null
+++ b/src/testing/benchmark.go
@@ -0,0 +1,822 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testing
+
+import (
+	"flag"
+	"fmt"
+	"internal/race"
+	"internal/sysinfo"
+	"io"
+	"math"
+	"os"
+	"runtime"
+	"sort"
+	"strconv"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"time"
+	"unicode"
+)
+
+func initBenchmarkFlags() {
+	matchBenchmarks = flag.String("test.bench", "", "run only benchmarks matching `regexp`")
+	benchmarkMemory = flag.Bool("test.benchmem", false, "print memory allocations for benchmarks")
+	flag.Var(&benchTime, "test.benchtime", "run each benchmark for duration `d`")
+}
+
+var (
+	matchBenchmarks *string
+	benchmarkMemory *bool
+
+	benchTime = benchTimeFlag{d: 1 * time.Second} // changed during test of testing package
+)
+
+type benchTimeFlag struct {
+	d time.Duration
+	n int
+}
+
+func (f *benchTimeFlag) String() string {
+	if f.n > 0 {
+		return fmt.Sprintf("%dx", f.n)
+	}
+	return time.Duration(f.d).String()
+}
+
+func (f *benchTimeFlag) Set(s string) error {
+	if strings.HasSuffix(s, "x") {
+		n, err := strconv.ParseInt(s[:len(s)-1], 10, 0)
+		if err != nil || n <= 0 {
+			return fmt.Errorf("invalid count")
+		}
+		*f = benchTimeFlag{n: int(n)}
+		return nil
+	}
+	d, err := time.ParseDuration(s)
+	if err != nil || d <= 0 {
+		return fmt.Errorf("invalid duration")
+	}
+	*f = benchTimeFlag{d: d}
+	return nil
+}
+
+// Global lock to ensure only one benchmark runs at a time.
+var benchmarkLock sync.Mutex
+
+// Used for every benchmark for measuring memory.
+var memStats runtime.MemStats
+
+// InternalBenchmark is an internal type but exported because it is cross-package;
+// it is part of the implementation of the "go test" command.
+type InternalBenchmark struct {
+	Name string
+	F    func(b *B)
+}
+
+// B is a type passed to Benchmark functions to manage benchmark
+// timing and to specify the number of iterations to run.
+//
+// A benchmark ends when its Benchmark function returns or calls any of the methods
+// FailNow, Fatal, Fatalf, SkipNow, Skip, or Skipf. Those methods must be called
+// only from the goroutine running the Benchmark function.
+// The other reporting methods, such as the variations of Log and Error,
+// may be called simultaneously from multiple goroutines.
+//
+// Like in tests, benchmark logs are accumulated during execution
+// and dumped to standard output when done. Unlike in tests, benchmark logs
+// are always printed, so as not to hide output whose existence may be
+// affecting benchmark results.
+type B struct {
+	common
+	importPath       string // import path of the package containing the benchmark
+	context          *benchContext
+	N                int
+	previousN        int           // number of iterations in the previous run
+	previousDuration time.Duration // total duration of the previous run
+	benchFunc        func(b *B)
+	benchTime        benchTimeFlag
+	bytes            int64
+	missingBytes     bool // one of the subbenchmarks does not have bytes set.
+	timerOn          bool
+	showAllocResult  bool
+	result           BenchmarkResult
+	parallelism      int // RunParallel creates parallelism*GOMAXPROCS goroutines
+	// The initial states of memStats.Mallocs and memStats.TotalAlloc.
+	startAllocs uint64
+	startBytes  uint64
+	// The net total of this test after being run.
+	netAllocs uint64
+	netBytes  uint64
+	// Extra metrics collected by ReportMetric.
+	extra map[string]float64
+}
+
+// StartTimer starts timing a test. This function is called automatically
+// before a benchmark starts, but it can also be used to resume timing after
+// a call to StopTimer.
+func (b *B) StartTimer() {
+	if !b.timerOn {
+		runtime.ReadMemStats(&memStats)
+		b.startAllocs = memStats.Mallocs
+		b.startBytes = memStats.TotalAlloc
+		b.start = time.Now()
+		b.timerOn = true
+	}
+}
+
+// StopTimer stops timing a test. This can be used to pause the timer
+// while performing complex initialization that you don't
+// want to measure.
+func (b *B) StopTimer() {
+	if b.timerOn {
+		b.duration += time.Since(b.start)
+		runtime.ReadMemStats(&memStats)
+		b.netAllocs += memStats.Mallocs - b.startAllocs
+		b.netBytes += memStats.TotalAlloc - b.startBytes
+		b.timerOn = false
+	}
+}
+
+// ResetTimer zeroes the elapsed benchmark time and memory allocation counters
+// and deletes user-reported metrics.
+// It does not affect whether the timer is running.
+func (b *B) ResetTimer() {
+	if b.extra == nil {
+		// Allocate the extra map before reading memory stats.
+		// Pre-size it to make more allocation unlikely.
+		b.extra = make(map[string]float64, 16)
+	} else {
+		for k := range b.extra {
+			delete(b.extra, k)
+		}
+	}
+	if b.timerOn {
+		runtime.ReadMemStats(&memStats)
+		b.startAllocs = memStats.Mallocs
+		b.startBytes = memStats.TotalAlloc
+		b.start = time.Now()
+	}
+	b.duration = 0
+	b.netAllocs = 0
+	b.netBytes = 0
+}
+
+// SetBytes records the number of bytes processed in a single operation.
+// If this is called, the benchmark will report ns/op and MB/s.
+func (b *B) SetBytes(n int64) { b.bytes = n }
+
+// ReportAllocs enables malloc statistics for this benchmark.
+// It is equivalent to setting -test.benchmem, but it only affects the
+// benchmark function that calls ReportAllocs.
+func (b *B) ReportAllocs() {
+	b.showAllocResult = true
+}
+
+// runN runs a single benchmark for the specified number of iterations.
+func (b *B) runN(n int) {
+	benchmarkLock.Lock()
+	defer benchmarkLock.Unlock()
+	defer b.runCleanup(normalPanic)
+	// Try to get a comparable environment for each run
+	// by clearing garbage from previous runs.
+	runtime.GC()
+	b.raceErrors = -race.Errors()
+	b.N = n
+	b.parallelism = 1
+	b.ResetTimer()
+	b.StartTimer()
+	b.benchFunc(b)
+	b.StopTimer()
+	b.previousN = n
+	b.previousDuration = b.duration
+	b.raceErrors += race.Errors()
+	if b.raceErrors > 0 {
+		b.Errorf("race detected during execution of benchmark")
+	}
+}
+
+func min(x, y int64) int64 {
+	if x > y {
+		return y
+	}
+	return x
+}
+
+func max(x, y int64) int64 {
+	if x < y {
+		return y
+	}
+	return x
+}
+
+// run1 runs the first iteration of benchFunc. It reports whether more
+// iterations of this benchmarks should be run.
+func (b *B) run1() bool {
+	if ctx := b.context; ctx != nil {
+		// Extend maxLen, if needed.
+		if n := len(b.name) + ctx.extLen + 1; n > ctx.maxLen {
+			ctx.maxLen = n + 8 // Add additional slack to avoid too many jumps in size.
+		}
+	}
+	go func() {
+		// Signal that we're done whether we return normally
+		// or by FailNow's runtime.Goexit.
+		defer func() {
+			b.signal <- true
+		}()
+
+		b.runN(1)
+	}()
+	<-b.signal
+	if b.failed {
+		fmt.Fprintf(b.w, "--- FAIL: %s\n%s", b.name, b.output)
+		return false
+	}
+	// Only print the output if we know we are not going to proceed.
+	// Otherwise it is printed in processBench.
+	if atomic.LoadInt32(&b.hasSub) != 0 || b.finished {
+		tag := "BENCH"
+		if b.skipped {
+			tag = "SKIP"
+		}
+		if b.chatty != nil && (len(b.output) > 0 || b.finished) {
+			b.trimOutput()
+			fmt.Fprintf(b.w, "--- %s: %s\n%s", tag, b.name, b.output)
+		}
+		return false
+	}
+	return true
+}
+
+var labelsOnce sync.Once
+
+// run executes the benchmark in a separate goroutine, including all of its
+// subbenchmarks. b must not have subbenchmarks.
+func (b *B) run() {
+	labelsOnce.Do(func() {
+		fmt.Fprintf(b.w, "goos: %s\n", runtime.GOOS)
+		fmt.Fprintf(b.w, "goarch: %s\n", runtime.GOARCH)
+		if b.importPath != "" {
+			fmt.Fprintf(b.w, "pkg: %s\n", b.importPath)
+		}
+		if cpu := sysinfo.CPU.Name(); cpu != "" {
+			fmt.Fprintf(b.w, "cpu: %s\n", cpu)
+		}
+	})
+	if b.context != nil {
+		// Running go test --test.bench
+		b.context.processBench(b) // Must call doBench.
+	} else {
+		// Running func Benchmark.
+		b.doBench()
+	}
+}
+
+func (b *B) doBench() BenchmarkResult {
+	go b.launch()
+	<-b.signal
+	return b.result
+}
+
+// launch launches the benchmark function. It gradually increases the number
+// of benchmark iterations until the benchmark runs for the requested benchtime.
+// launch is run by the doBench function as a separate goroutine.
+// run1 must have been called on b.
+func (b *B) launch() {
+	// Signal that we're done whether we return normally
+	// or by FailNow's runtime.Goexit.
+	defer func() {
+		b.signal <- true
+	}()
+
+	// Run the benchmark for at least the specified amount of time.
+	if b.benchTime.n > 0 {
+		b.runN(b.benchTime.n)
+	} else {
+		d := b.benchTime.d
+		for n := int64(1); !b.failed && b.duration < d && n < 1e9; {
+			last := n
+			// Predict required iterations.
+			goalns := d.Nanoseconds()
+			prevIters := int64(b.N)
+			prevns := b.duration.Nanoseconds()
+			if prevns <= 0 {
+				// Round up, to avoid div by zero.
+				prevns = 1
+			}
+			// Order of operations matters.
+			// For very fast benchmarks, prevIters ~= prevns.
+			// If you divide first, you get 0 or 1,
+			// which can hide an order of magnitude in execution time.
+			// So multiply first, then divide.
+			n = goalns * prevIters / prevns
+			// Run more iterations than we think we'll need (1.2x).
+			n += n / 5
+			// Don't grow too fast in case we had timing errors previously.
+			n = min(n, 100*last)
+			// Be sure to run at least one more than last time.
+			n = max(n, last+1)
+			// Don't run more than 1e9 times. (This also keeps n in int range on 32 bit platforms.)
+			n = min(n, 1e9)
+			b.runN(int(n))
+		}
+	}
+	b.result = BenchmarkResult{b.N, b.duration, b.bytes, b.netAllocs, b.netBytes, b.extra}
+}
+
+// ReportMetric adds "n unit" to the reported benchmark results.
+// If the metric is per-iteration, the caller should divide by b.N,
+// and by convention units should end in "/op".
+// ReportMetric overrides any previously reported value for the same unit.
+// ReportMetric panics if unit is the empty string or if unit contains
+// any whitespace.
+// If unit is a unit normally reported by the benchmark framework itself
+// (such as "allocs/op"), ReportMetric will override that metric.
+// Setting "ns/op" to 0 will suppress that built-in metric.
+func (b *B) ReportMetric(n float64, unit string) {
+	if unit == "" {
+		panic("metric unit must not be empty")
+	}
+	if strings.IndexFunc(unit, unicode.IsSpace) >= 0 {
+		panic("metric unit must not contain whitespace")
+	}
+	b.extra[unit] = n
+}
+
+// BenchmarkResult contains the results of a benchmark run.
+type BenchmarkResult struct {
+	N         int           // The number of iterations.
+	T         time.Duration // The total time taken.
+	Bytes     int64         // Bytes processed in one iteration.
+	MemAllocs uint64        // The total number of memory allocations.
+	MemBytes  uint64        // The total number of bytes allocated.
+
+	// Extra records additional metrics reported by ReportMetric.
+	Extra map[string]float64
+}
+
+// NsPerOp returns the "ns/op" metric.
+func (r BenchmarkResult) NsPerOp() int64 {
+	if v, ok := r.Extra["ns/op"]; ok {
+		return int64(v)
+	}
+	if r.N <= 0 {
+		return 0
+	}
+	return r.T.Nanoseconds() / int64(r.N)
+}
+
+// mbPerSec returns the "MB/s" metric.
+func (r BenchmarkResult) mbPerSec() float64 {
+	if v, ok := r.Extra["MB/s"]; ok {
+		return v
+	}
+	if r.Bytes <= 0 || r.T <= 0 || r.N <= 0 {
+		return 0
+	}
+	return (float64(r.Bytes) * float64(r.N) / 1e6) / r.T.Seconds()
+}
+
+// AllocsPerOp returns the "allocs/op" metric,
+// which is calculated as r.MemAllocs / r.N.
+func (r BenchmarkResult) AllocsPerOp() int64 {
+	if v, ok := r.Extra["allocs/op"]; ok {
+		return int64(v)
+	}
+	if r.N <= 0 {
+		return 0
+	}
+	return int64(r.MemAllocs) / int64(r.N)
+}
+
+// AllocedBytesPerOp returns the "B/op" metric,
+// which is calculated as r.MemBytes / r.N.
+func (r BenchmarkResult) AllocedBytesPerOp() int64 {
+	if v, ok := r.Extra["B/op"]; ok {
+		return int64(v)
+	}
+	if r.N <= 0 {
+		return 0
+	}
+	return int64(r.MemBytes) / int64(r.N)
+}
+
+// String returns a summary of the benchmark results.
+// It follows the benchmark result line format from
+// https://golang.org/design/14313-benchmark-format, not including the
+// benchmark name.
+// Extra metrics override built-in metrics of the same name.
+// String does not include allocs/op or B/op, since those are reported
+// by MemString.
+func (r BenchmarkResult) String() string {
+	buf := new(strings.Builder)
+	fmt.Fprintf(buf, "%8d", r.N)
+
+	// Get ns/op as a float.
+	ns, ok := r.Extra["ns/op"]
+	if !ok {
+		ns = float64(r.T.Nanoseconds()) / float64(r.N)
+	}
+	if ns != 0 {
+		buf.WriteByte('\t')
+		prettyPrint(buf, ns, "ns/op")
+	}
+
+	if mbs := r.mbPerSec(); mbs != 0 {
+		fmt.Fprintf(buf, "\t%7.2f MB/s", mbs)
+	}
+
+	// Print extra metrics that aren't represented in the standard
+	// metrics.
+	var extraKeys []string
+	for k := range r.Extra {
+		switch k {
+		case "ns/op", "MB/s", "B/op", "allocs/op":
+			// Built-in metrics reported elsewhere.
+			continue
+		}
+		extraKeys = append(extraKeys, k)
+	}
+	sort.Strings(extraKeys)
+	for _, k := range extraKeys {
+		buf.WriteByte('\t')
+		prettyPrint(buf, r.Extra[k], k)
+	}
+	return buf.String()
+}
+
+func prettyPrint(w io.Writer, x float64, unit string) {
+	// Print all numbers with 10 places before the decimal point
+	// and small numbers with four sig figs. Field widths are
+	// chosen to fit the whole part in 10 places while aligning
+	// the decimal point of all fractional formats.
+	var format string
+	switch y := math.Abs(x); {
+	case y == 0 || y >= 999.95:
+		format = "%10.0f %s"
+	case y >= 99.995:
+		format = "%12.1f %s"
+	case y >= 9.9995:
+		format = "%13.2f %s"
+	case y >= 0.99995:
+		format = "%14.3f %s"
+	case y >= 0.099995:
+		format = "%15.4f %s"
+	case y >= 0.0099995:
+		format = "%16.5f %s"
+	case y >= 0.00099995:
+		format = "%17.6f %s"
+	default:
+		format = "%18.7f %s"
+	}
+	fmt.Fprintf(w, format, x, unit)
+}
+
+// MemString returns r.AllocedBytesPerOp and r.AllocsPerOp in the same format as 'go test'.
+func (r BenchmarkResult) MemString() string {
+	return fmt.Sprintf("%8d B/op\t%8d allocs/op",
+		r.AllocedBytesPerOp(), r.AllocsPerOp())
+}
+
+// benchmarkName returns full name of benchmark including procs suffix.
+func benchmarkName(name string, n int) string {
+	if n != 1 {
+		return fmt.Sprintf("%s-%d", name, n)
+	}
+	return name
+}
+
+type benchContext struct {
+	match *matcher
+
+	maxLen int // The largest recorded benchmark name.
+	extLen int // Maximum extension length.
+}
+
+// RunBenchmarks is an internal function but exported because it is cross-package;
+// it is part of the implementation of the "go test" command.
+func RunBenchmarks(matchString func(pat, str string) (bool, error), benchmarks []InternalBenchmark) {
+	runBenchmarks("", matchString, benchmarks)
+}
+
+func runBenchmarks(importPath string, matchString func(pat, str string) (bool, error), benchmarks []InternalBenchmark) bool {
+	// If no flag was specified, don't run benchmarks.
+	if len(*matchBenchmarks) == 0 {
+		return true
+	}
+	// Collect matching benchmarks and determine longest name.
+	maxprocs := 1
+	for _, procs := range cpuList {
+		if procs > maxprocs {
+			maxprocs = procs
+		}
+	}
+	ctx := &benchContext{
+		match:  newMatcher(matchString, *matchBenchmarks, "-test.bench"),
+		extLen: len(benchmarkName("", maxprocs)),
+	}
+	var bs []InternalBenchmark
+	for _, Benchmark := range benchmarks {
+		if _, matched, _ := ctx.match.fullName(nil, Benchmark.Name); matched {
+			bs = append(bs, Benchmark)
+			benchName := benchmarkName(Benchmark.Name, maxprocs)
+			if l := len(benchName) + ctx.extLen + 1; l > ctx.maxLen {
+				ctx.maxLen = l
+			}
+		}
+	}
+	main := &B{
+		common: common{
+			name:  "Main",
+			w:     os.Stdout,
+			bench: true,
+		},
+		importPath: importPath,
+		benchFunc: func(b *B) {
+			for _, Benchmark := range bs {
+				b.Run(Benchmark.Name, Benchmark.F)
+			}
+		},
+		benchTime: benchTime,
+		context:   ctx,
+	}
+	if Verbose() {
+		main.chatty = newChattyPrinter(main.w)
+	}
+	main.runN(1)
+	return !main.failed
+}
+
+// processBench runs bench b for the configured CPU counts and prints the results.
+func (ctx *benchContext) processBench(b *B) {
+	for i, procs := range cpuList {
+		for j := uint(0); j < *count; j++ {
+			runtime.GOMAXPROCS(procs)
+			benchName := benchmarkName(b.name, procs)
+
+			// If it's chatty, we've already printed this information.
+			if b.chatty == nil {
+				fmt.Fprintf(b.w, "%-*s\t", ctx.maxLen, benchName)
+			}
+			// Recompute the running time for all but the first iteration.
+			if i > 0 || j > 0 {
+				b = &B{
+					common: common{
+						signal: make(chan bool),
+						name:   b.name,
+						w:      b.w,
+						chatty: b.chatty,
+						bench:  true,
+					},
+					benchFunc: b.benchFunc,
+					benchTime: b.benchTime,
+				}
+				b.run1()
+			}
+			r := b.doBench()
+			if b.failed {
+				// The output could be very long here, but probably isn't.
+				// We print it all, regardless, because we don't want to trim the reason
+				// the benchmark failed.
+				fmt.Fprintf(b.w, "--- FAIL: %s\n%s", benchName, b.output)
+				continue
+			}
+			results := r.String()
+			if b.chatty != nil {
+				fmt.Fprintf(b.w, "%-*s\t", ctx.maxLen, benchName)
+			}
+			if *benchmarkMemory || b.showAllocResult {
+				results += "\t" + r.MemString()
+			}
+			fmt.Fprintln(b.w, results)
+			// Unlike with tests, we ignore the -chatty flag and always print output for
+			// benchmarks since the output generation time will skew the results.
+			if len(b.output) > 0 {
+				b.trimOutput()
+				fmt.Fprintf(b.w, "--- BENCH: %s\n%s", benchName, b.output)
+			}
+			if p := runtime.GOMAXPROCS(-1); p != procs {
+				fmt.Fprintf(os.Stderr, "testing: %s left GOMAXPROCS set to %d\n", benchName, p)
+			}
+		}
+	}
+}
+
+// Run benchmarks f as a subbenchmark with the given name. It reports
+// whether there were any failures.
+//
+// A subbenchmark is like any other benchmark. A benchmark that calls Run at
+// least once will not be measured itself and will be called once with N=1.
+func (b *B) Run(name string, f func(b *B)) bool {
+	// Since b has subbenchmarks, we will no longer run it as a benchmark itself.
+	// Release the lock and acquire it on exit to ensure locks stay paired.
+	atomic.StoreInt32(&b.hasSub, 1)
+	benchmarkLock.Unlock()
+	defer benchmarkLock.Lock()
+
+	benchName, ok, partial := b.name, true, false
+	if b.context != nil {
+		benchName, ok, partial = b.context.match.fullName(&b.common, name)
+	}
+	if !ok {
+		return true
+	}
+	var pc [maxStackLen]uintptr
+	n := runtime.Callers(2, pc[:])
+	sub := &B{
+		common: common{
+			signal:  make(chan bool),
+			name:    benchName,
+			parent:  &b.common,
+			level:   b.level + 1,
+			creator: pc[:n],
+			w:       b.w,
+			chatty:  b.chatty,
+			bench:   true,
+		},
+		importPath: b.importPath,
+		benchFunc:  f,
+		benchTime:  b.benchTime,
+		context:    b.context,
+	}
+	if partial {
+		// Partial name match, like -bench=X/Y matching BenchmarkX.
+		// Only process sub-benchmarks, if any.
+		atomic.StoreInt32(&sub.hasSub, 1)
+	}
+
+	if b.chatty != nil {
+		labelsOnce.Do(func() {
+			fmt.Printf("goos: %s\n", runtime.GOOS)
+			fmt.Printf("goarch: %s\n", runtime.GOARCH)
+			if b.importPath != "" {
+				fmt.Printf("pkg: %s\n", b.importPath)
+			}
+			if cpu := sysinfo.CPU.Name(); cpu != "" {
+				fmt.Printf("cpu: %s\n", cpu)
+			}
+		})
+
+		fmt.Println(benchName)
+	}
+
+	if sub.run1() {
+		sub.run()
+	}
+	b.add(sub.result)
+	return !sub.failed
+}
+
+// add simulates running benchmarks in sequence in a single iteration. It is
+// used to give some meaningful results in case func Benchmark is used in
+// combination with Run.
+func (b *B) add(other BenchmarkResult) {
+	r := &b.result
+	// The aggregated BenchmarkResults resemble running all subbenchmarks as
+	// in sequence in a single benchmark.
+	r.N = 1
+	r.T += time.Duration(other.NsPerOp())
+	if other.Bytes == 0 {
+		// Summing Bytes is meaningless in aggregate if not all subbenchmarks
+		// set it.
+		b.missingBytes = true
+		r.Bytes = 0
+	}
+	if !b.missingBytes {
+		r.Bytes += other.Bytes
+	}
+	r.MemAllocs += uint64(other.AllocsPerOp())
+	r.MemBytes += uint64(other.AllocedBytesPerOp())
+}
+
+// trimOutput shortens the output from a benchmark, which can be very long.
+func (b *B) trimOutput() {
+	// The output is likely to appear multiple times because the benchmark
+	// is run multiple times, but at least it will be seen. This is not a big deal
+	// because benchmarks rarely print, but just in case, we trim it if it's too long.
+	const maxNewlines = 10
+	for nlCount, j := 0, 0; j < len(b.output); j++ {
+		if b.output[j] == '\n' {
+			nlCount++
+			if nlCount >= maxNewlines {
+				b.output = append(b.output[:j], "\n\t... [output truncated]\n"...)
+				break
+			}
+		}
+	}
+}
+
+// A PB is used by RunParallel for running parallel benchmarks.
+type PB struct {
+	globalN *uint64 // shared between all worker goroutines iteration counter
+	grain   uint64  // acquire that many iterations from globalN at once
+	cache   uint64  // local cache of acquired iterations
+	bN      uint64  // total number of iterations to execute (b.N)
+}
+
+// Next reports whether there are more iterations to execute.
+func (pb *PB) Next() bool {
+	if pb.cache == 0 {
+		n := atomic.AddUint64(pb.globalN, pb.grain)
+		if n <= pb.bN {
+			pb.cache = pb.grain
+		} else if n < pb.bN+pb.grain {
+			pb.cache = pb.bN + pb.grain - n
+		} else {
+			return false
+		}
+	}
+	pb.cache--
+	return true
+}
+
+// RunParallel runs a benchmark in parallel.
+// It creates multiple goroutines and distributes b.N iterations among them.
+// The number of goroutines defaults to GOMAXPROCS. To increase parallelism for
+// non-CPU-bound benchmarks, call SetParallelism before RunParallel.
+// RunParallel is usually used with the go test -cpu flag.
+//
+// The body function will be run in each goroutine. It should set up any
+// goroutine-local state and then iterate until pb.Next returns false.
+// It should not use the StartTimer, StopTimer, or ResetTimer functions,
+// because they have global effect. It should also not call Run.
+func (b *B) RunParallel(body func(*PB)) {
+	if b.N == 0 {
+		return // Nothing to do when probing.
+	}
+	// Calculate grain size as number of iterations that take ~100µs.
+	// 100µs is enough to amortize the overhead and provide sufficient
+	// dynamic load balancing.
+	grain := uint64(0)
+	if b.previousN > 0 && b.previousDuration > 0 {
+		grain = 1e5 * uint64(b.previousN) / uint64(b.previousDuration)
+	}
+	if grain < 1 {
+		grain = 1
+	}
+	// We expect the inner loop and function call to take at least 10ns,
+	// so do not do more than 100µs/10ns=1e4 iterations.
+	if grain > 1e4 {
+		grain = 1e4
+	}
+
+	n := uint64(0)
+	numProcs := b.parallelism * runtime.GOMAXPROCS(0)
+	var wg sync.WaitGroup
+	wg.Add(numProcs)
+	for p := 0; p < numProcs; p++ {
+		go func() {
+			defer wg.Done()
+			pb := &PB{
+				globalN: &n,
+				grain:   grain,
+				bN:      uint64(b.N),
+			}
+			body(pb)
+		}()
+	}
+	wg.Wait()
+	if n <= uint64(b.N) && !b.Failed() {
+		b.Fatal("RunParallel: body exited without pb.Next() == false")
+	}
+}
+
+// SetParallelism sets the number of goroutines used by RunParallel to p*GOMAXPROCS.
+// There is usually no need to call SetParallelism for CPU-bound benchmarks.
+// If p is less than 1, this call will have no effect.
+func (b *B) SetParallelism(p int) {
+	if p >= 1 {
+		b.parallelism = p
+	}
+}
+
+// Benchmark benchmarks a single function. It is useful for creating
+// custom benchmarks that do not use the "go test" command.
+//
+// If f depends on testing flags, then Init must be used to register
+// those flags before calling Benchmark and before calling flag.Parse.
+//
+// If f calls Run, the result will be an estimate of running all its
+// subbenchmarks that don't call Run in sequence in a single benchmark.
+func Benchmark(f func(b *B)) BenchmarkResult {
+	b := &B{
+		common: common{
+			signal: make(chan bool),
+			w:      discard{},
+		},
+		benchFunc: f,
+		benchTime: benchTime,
+	}
+	if b.run1() {
+		b.run()
+	}
+	return b.result
+}
+
+type discard struct{}
+
+func (discard) Write(b []byte) (n int, err error) { return len(b), nil }
diff --git a/src/testing/benchmark_test.go b/src/testing/benchmark_test.go
new file mode 100644
index 0000000..4c1cbd1
--- /dev/null
+++ b/src/testing/benchmark_test.go
@@ -0,0 +1,156 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testing_test
+
+import (
+	"bytes"
+	"runtime"
+	"sort"
+	"strings"
+	"sync/atomic"
+	"testing"
+	"text/template"
+	"time"
+)
+
+var prettyPrintTests = []struct {
+	v        float64
+	expected string
+}{
+	{0, "         0 x"},
+	{1234.1, "      1234 x"},
+	{-1234.1, "     -1234 x"},
+	{999.950001, "      1000 x"},
+	{999.949999, "       999.9 x"},
+	{99.9950001, "       100.0 x"},
+	{99.9949999, "        99.99 x"},
+	{-99.9949999, "       -99.99 x"},
+	{0.000999950001, "         0.001000 x"},
+	{0.000999949999, "         0.0009999 x"}, // smallest case
+	{0.0000999949999, "         0.0001000 x"},
+}
+
+func TestPrettyPrint(t *testing.T) {
+	for _, tt := range prettyPrintTests {
+		buf := new(strings.Builder)
+		testing.PrettyPrint(buf, tt.v, "x")
+		if tt.expected != buf.String() {
+			t.Errorf("prettyPrint(%v): expected %q, actual %q", tt.v, tt.expected, buf.String())
+		}
+	}
+}
+
+func TestResultString(t *testing.T) {
+	// Test fractional ns/op handling
+	r := testing.BenchmarkResult{
+		N: 100,
+		T: 240 * time.Nanosecond,
+	}
+	if r.NsPerOp() != 2 {
+		t.Errorf("NsPerOp: expected 2, actual %v", r.NsPerOp())
+	}
+	if want, got := "     100\t         2.400 ns/op", r.String(); want != got {
+		t.Errorf("String: expected %q, actual %q", want, got)
+	}
+
+	// Test sub-1 ns/op (issue #31005)
+	r.T = 40 * time.Nanosecond
+	if want, got := "     100\t         0.4000 ns/op", r.String(); want != got {
+		t.Errorf("String: expected %q, actual %q", want, got)
+	}
+
+	// Test 0 ns/op
+	r.T = 0
+	if want, got := "     100", r.String(); want != got {
+		t.Errorf("String: expected %q, actual %q", want, got)
+	}
+}
+
+func TestRunParallel(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping in short mode")
+	}
+	testing.Benchmark(func(b *testing.B) {
+		procs := uint32(0)
+		iters := uint64(0)
+		b.SetParallelism(3)
+		b.RunParallel(func(pb *testing.PB) {
+			atomic.AddUint32(&procs, 1)
+			for pb.Next() {
+				atomic.AddUint64(&iters, 1)
+			}
+		})
+		if want := uint32(3 * runtime.GOMAXPROCS(0)); procs != want {
+			t.Errorf("got %v procs, want %v", procs, want)
+		}
+		if iters != uint64(b.N) {
+			t.Errorf("got %v iters, want %v", iters, b.N)
+		}
+	})
+}
+
+func TestRunParallelFail(t *testing.T) {
+	testing.Benchmark(func(b *testing.B) {
+		b.RunParallel(func(pb *testing.PB) {
+			// The function must be able to log/abort
+			// w/o crashing/deadlocking the whole benchmark.
+			b.Log("log")
+			b.Error("error")
+		})
+	})
+}
+
+func ExampleB_RunParallel() {
+	// Parallel benchmark for text/template.Template.Execute on a single object.
+	testing.Benchmark(func(b *testing.B) {
+		templ := template.Must(template.New("test").Parse("Hello, {{.}}!"))
+		// RunParallel will create GOMAXPROCS goroutines
+		// and distribute work among them.
+		b.RunParallel(func(pb *testing.PB) {
+			// Each goroutine has its own bytes.Buffer.
+			var buf bytes.Buffer
+			for pb.Next() {
+				// The loop body is executed b.N times total across all goroutines.
+				buf.Reset()
+				templ.Execute(&buf, "World")
+			}
+		})
+	})
+}
+
+func TestReportMetric(t *testing.T) {
+	res := testing.Benchmark(func(b *testing.B) {
+		b.ReportMetric(12345, "ns/op")
+		b.ReportMetric(0.2, "frobs/op")
+	})
+	// Test built-in overriding.
+	if res.NsPerOp() != 12345 {
+		t.Errorf("NsPerOp: expected %v, actual %v", 12345, res.NsPerOp())
+	}
+	// Test stringing.
+	res.N = 1 // Make the output stable
+	want := "       1\t     12345 ns/op\t         0.2000 frobs/op"
+	if want != res.String() {
+		t.Errorf("expected %q, actual %q", want, res.String())
+	}
+}
+
+func ExampleB_ReportMetric() {
+	// This reports a custom benchmark metric relevant to a
+	// specific algorithm (in this case, sorting).
+	testing.Benchmark(func(b *testing.B) {
+		var compares int64
+		for i := 0; i < b.N; i++ {
+			s := []int{5, 4, 3, 2, 1}
+			sort.Slice(s, func(i, j int) bool {
+				compares++
+				return s[i] < s[j]
+			})
+		}
+		// This metric is per-operation, so divide by b.N and
+		// report it as a "/op" unit.
+		b.ReportMetric(float64(compares)/float64(b.N), "compares/op")
+	})
+}
diff --git a/src/testing/cover.go b/src/testing/cover.go
new file mode 100644
index 0000000..62ee5ac
--- /dev/null
+++ b/src/testing/cover.go
@@ -0,0 +1,116 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Support for test coverage.
+
+package testing
+
+import (
+	"fmt"
+	"os"
+	"sync/atomic"
+)
+
+// CoverBlock records the coverage data for a single basic block.
+// The fields are 1-indexed, as in an editor: The opening line of
+// the file is number 1, for example. Columns are measured
+// in bytes.
+// NOTE: This struct is internal to the testing infrastructure and may change.
+// It is not covered (yet) by the Go 1 compatibility guidelines.
+type CoverBlock struct {
+	Line0 uint32 // Line number for block start.
+	Col0  uint16 // Column number for block start.
+	Line1 uint32 // Line number for block end.
+	Col1  uint16 // Column number for block end.
+	Stmts uint16 // Number of statements included in this block.
+}
+
+var cover Cover
+
+// Cover records information about test coverage checking.
+// NOTE: This struct is internal to the testing infrastructure and may change.
+// It is not covered (yet) by the Go 1 compatibility guidelines.
+type Cover struct {
+	Mode            string
+	Counters        map[string][]uint32
+	Blocks          map[string][]CoverBlock
+	CoveredPackages string
+}
+
+// Coverage reports the current code coverage as a fraction in the range [0, 1].
+// If coverage is not enabled, Coverage returns 0.
+//
+// When running a large set of sequential test cases, checking Coverage after each one
+// can be useful for identifying which test cases exercise new code paths.
+// It is not a replacement for the reports generated by 'go test -cover' and
+// 'go tool cover'.
+func Coverage() float64 {
+	var n, d int64
+	for _, counters := range cover.Counters {
+		for i := range counters {
+			if atomic.LoadUint32(&counters[i]) > 0 {
+				n++
+			}
+			d++
+		}
+	}
+	if d == 0 {
+		return 0
+	}
+	return float64(n) / float64(d)
+}
+
+// RegisterCover records the coverage data accumulators for the tests.
+// NOTE: This function is internal to the testing infrastructure and may change.
+// It is not covered (yet) by the Go 1 compatibility guidelines.
+func RegisterCover(c Cover) {
+	cover = c
+}
+
+// mustBeNil checks the error and, if present, reports it and exits.
+func mustBeNil(err error) {
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "testing: %s\n", err)
+		os.Exit(2)
+	}
+}
+
+// coverReport reports the coverage percentage and writes a coverage profile if requested.
+func coverReport() {
+	var f *os.File
+	var err error
+	if *coverProfile != "" {
+		f, err = os.Create(toOutputDir(*coverProfile))
+		mustBeNil(err)
+		fmt.Fprintf(f, "mode: %s\n", cover.Mode)
+		defer func() { mustBeNil(f.Close()) }()
+	}
+
+	var active, total int64
+	var count uint32
+	for name, counts := range cover.Counters {
+		blocks := cover.Blocks[name]
+		for i := range counts {
+			stmts := int64(blocks[i].Stmts)
+			total += stmts
+			count = atomic.LoadUint32(&counts[i]) // For -mode=atomic.
+			if count > 0 {
+				active += stmts
+			}
+			if f != nil {
+				_, err := fmt.Fprintf(f, "%s:%d.%d,%d.%d %d %d\n", name,
+					blocks[i].Line0, blocks[i].Col0,
+					blocks[i].Line1, blocks[i].Col1,
+					stmts,
+					count)
+				mustBeNil(err)
+			}
+		}
+	}
+	if total == 0 {
+		fmt.Println("coverage: [no statements]")
+		return
+	}
+	fmt.Printf("coverage: %.1f%% of statements%s\n", 100*float64(active)/float64(total), cover.CoveredPackages)
+}
diff --git a/src/testing/example.go b/src/testing/example.go
new file mode 100644
index 0000000..0217c5d
--- /dev/null
+++ b/src/testing/example.go
@@ -0,0 +1,98 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testing
+
+import (
+	"fmt"
+	"os"
+	"sort"
+	"strings"
+	"time"
+)
+
+type InternalExample struct {
+	Name      string
+	F         func()
+	Output    string
+	Unordered bool
+}
+
+// RunExamples is an internal function but exported because it is cross-package;
+// it is part of the implementation of the "go test" command.
+func RunExamples(matchString func(pat, str string) (bool, error), examples []InternalExample) (ok bool) {
+	_, ok = runExamples(matchString, examples)
+	return ok
+}
+
+func runExamples(matchString func(pat, str string) (bool, error), examples []InternalExample) (ran, ok bool) {
+	ok = true
+
+	var eg InternalExample
+
+	for _, eg = range examples {
+		matched, err := matchString(*match, eg.Name)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "testing: invalid regexp for -test.run: %s\n", err)
+			os.Exit(1)
+		}
+		if !matched {
+			continue
+		}
+		ran = true
+		if !runExample(eg) {
+			ok = false
+		}
+	}
+
+	return ran, ok
+}
+
+func sortLines(output string) string {
+	lines := strings.Split(output, "\n")
+	sort.Strings(lines)
+	return strings.Join(lines, "\n")
+}
+
+// processRunResult computes a summary and status of the result of running an example test.
+// stdout is the captured output from stdout of the test.
+// recovered is the result of invoking recover after running the test, in case it panicked.
+//
+// If stdout doesn't match the expected output or if recovered is non-nil, it'll print the cause of failure to stdout.
+// If the test is chatty/verbose, it'll print a success message to stdout.
+// If recovered is non-nil, it'll panic with that value.
+// If the test panicked with nil, or invoked runtime.Goexit, it'll be
+// made to fail and panic with errNilPanicOrGoexit
+func (eg *InternalExample) processRunResult(stdout string, timeSpent time.Duration, finished bool, recovered interface{}) (passed bool) {
+	passed = true
+	dstr := fmtDuration(timeSpent)
+	var fail string
+	got := strings.TrimSpace(stdout)
+	want := strings.TrimSpace(eg.Output)
+	if eg.Unordered {
+		if sortLines(got) != sortLines(want) && recovered == nil {
+			fail = fmt.Sprintf("got:\n%s\nwant (unordered):\n%s\n", stdout, eg.Output)
+		}
+	} else {
+		if got != want && recovered == nil {
+			fail = fmt.Sprintf("got:\n%s\nwant:\n%s\n", got, want)
+		}
+	}
+	if fail != "" || !finished || recovered != nil {
+		fmt.Printf("--- FAIL: %s (%s)\n%s", eg.Name, dstr, fail)
+		passed = false
+	} else if *chatty {
+		fmt.Printf("--- PASS: %s (%s)\n", eg.Name, dstr)
+	}
+
+	if recovered != nil {
+		// Propagate the previously recovered result, by panicking.
+		panic(recovered)
+	}
+	if !finished && recovered == nil {
+		panic(errNilPanicOrGoexit)
+	}
+
+	return
+}
diff --git a/src/testing/export_test.go b/src/testing/export_test.go
new file mode 100644
index 0000000..0022491
--- /dev/null
+++ b/src/testing/export_test.go
@@ -0,0 +1,7 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testing
+
+var PrettyPrint = prettyPrint
diff --git a/src/testing/fstest/mapfs.go b/src/testing/fstest/mapfs.go
new file mode 100644
index 0000000..a5d4a23
--- /dev/null
+++ b/src/testing/fstest/mapfs.go
@@ -0,0 +1,238 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package fstest
+
+import (
+	"io"
+	"io/fs"
+	"path"
+	"sort"
+	"strings"
+	"time"
+)
+
+// A MapFS is a simple in-memory file system for use in tests,
+// represented as a map from path names (arguments to Open)
+// to information about the files or directories they represent.
+//
+// The map need not include parent directories for files contained
+// in the map; those will be synthesized if needed.
+// But a directory can still be included by setting the MapFile.Mode's ModeDir bit;
+// this may be necessary for detailed control over the directory's FileInfo
+// or to create an empty directory.
+//
+// File system operations read directly from the map,
+// so that the file system can be changed by editing the map as needed.
+// An implication is that file system operations must not run concurrently
+// with changes to the map, which would be a race.
+// Another implication is that opening or reading a directory requires
+// iterating over the entire map, so a MapFS should typically be used with not more
+// than a few hundred entries or directory reads.
+type MapFS map[string]*MapFile
+
+// A MapFile describes a single file in a MapFS.
+type MapFile struct {
+	Data    []byte      // file content
+	Mode    fs.FileMode // FileInfo.Mode
+	ModTime time.Time   // FileInfo.ModTime
+	Sys     interface{} // FileInfo.Sys
+}
+
+var _ fs.FS = MapFS(nil)
+var _ fs.File = (*openMapFile)(nil)
+
+// Open opens the named file.
+func (fsys MapFS) Open(name string) (fs.File, error) {
+	if !fs.ValidPath(name) {
+		return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrNotExist}
+	}
+	file := fsys[name]
+	if file != nil && file.Mode&fs.ModeDir == 0 {
+		// Ordinary file
+		return &openMapFile{name, mapFileInfo{path.Base(name), file}, 0}, nil
+	}
+
+	// Directory, possibly synthesized.
+	// Note that file can be nil here: the map need not contain explicit parent directories for all its files.
+	// But file can also be non-nil, in case the user wants to set metadata for the directory explicitly.
+	// Either way, we need to construct the list of children of this directory.
+	var list []mapFileInfo
+	var elem string
+	var need = make(map[string]bool)
+	if name == "." {
+		elem = "."
+		for fname, f := range fsys {
+			i := strings.Index(fname, "/")
+			if i < 0 {
+				list = append(list, mapFileInfo{fname, f})
+			} else {
+				need[fname[:i]] = true
+			}
+		}
+	} else {
+		elem = name[strings.LastIndex(name, "/")+1:]
+		prefix := name + "/"
+		for fname, f := range fsys {
+			if strings.HasPrefix(fname, prefix) {
+				felem := fname[len(prefix):]
+				i := strings.Index(felem, "/")
+				if i < 0 {
+					list = append(list, mapFileInfo{felem, f})
+				} else {
+					need[fname[len(prefix):len(prefix)+i]] = true
+				}
+			}
+		}
+		// If the directory name is not in the map,
+		// and there are no children of the name in the map,
+		// then the directory is treated as not existing.
+		if file == nil && list == nil && len(need) == 0 {
+			return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrNotExist}
+		}
+	}
+	for _, fi := range list {
+		delete(need, fi.name)
+	}
+	for name := range need {
+		list = append(list, mapFileInfo{name, &MapFile{Mode: fs.ModeDir}})
+	}
+	sort.Slice(list, func(i, j int) bool {
+		return list[i].name < list[j].name
+	})
+
+	if file == nil {
+		file = &MapFile{Mode: fs.ModeDir}
+	}
+	return &mapDir{name, mapFileInfo{elem, file}, list, 0}, nil
+}
+
+// fsOnly is a wrapper that hides all but the fs.FS methods,
+// to avoid an infinite recursion when implementing special
+// methods in terms of helpers that would use them.
+// (In general, implementing these methods using the package fs helpers
+// is redundant and unnecessary, but having the methods may make
+// MapFS exercise more code paths when used in tests.)
+type fsOnly struct{ fs.FS }
+
+func (fsys MapFS) ReadFile(name string) ([]byte, error) {
+	return fs.ReadFile(fsOnly{fsys}, name)
+}
+
+func (fsys MapFS) Stat(name string) (fs.FileInfo, error) {
+	return fs.Stat(fsOnly{fsys}, name)
+}
+
+func (fsys MapFS) ReadDir(name string) ([]fs.DirEntry, error) {
+	return fs.ReadDir(fsOnly{fsys}, name)
+}
+
+func (fsys MapFS) Glob(pattern string) ([]string, error) {
+	return fs.Glob(fsOnly{fsys}, pattern)
+}
+
+type noSub struct {
+	MapFS
+}
+
+func (noSub) Sub() {} // not the fs.SubFS signature
+
+func (fsys MapFS) Sub(dir string) (fs.FS, error) {
+	return fs.Sub(noSub{fsys}, dir)
+}
+
+// A mapFileInfo implements fs.FileInfo and fs.DirEntry for a given map file.
+type mapFileInfo struct {
+	name string
+	f    *MapFile
+}
+
+func (i *mapFileInfo) Name() string               { return i.name }
+func (i *mapFileInfo) Size() int64                { return int64(len(i.f.Data)) }
+func (i *mapFileInfo) Mode() fs.FileMode          { return i.f.Mode }
+func (i *mapFileInfo) Type() fs.FileMode          { return i.f.Mode.Type() }
+func (i *mapFileInfo) ModTime() time.Time         { return i.f.ModTime }
+func (i *mapFileInfo) IsDir() bool                { return i.f.Mode&fs.ModeDir != 0 }
+func (i *mapFileInfo) Sys() interface{}           { return i.f.Sys }
+func (i *mapFileInfo) Info() (fs.FileInfo, error) { return i, nil }
+
+// An openMapFile is a regular (non-directory) fs.File open for reading.
+type openMapFile struct {
+	path string
+	mapFileInfo
+	offset int64
+}
+
+func (f *openMapFile) Stat() (fs.FileInfo, error) { return &f.mapFileInfo, nil }
+
+func (f *openMapFile) Close() error { return nil }
+
+func (f *openMapFile) Read(b []byte) (int, error) {
+	if f.offset >= int64(len(f.f.Data)) {
+		return 0, io.EOF
+	}
+	if f.offset < 0 {
+		return 0, &fs.PathError{Op: "read", Path: f.path, Err: fs.ErrInvalid}
+	}
+	n := copy(b, f.f.Data[f.offset:])
+	f.offset += int64(n)
+	return n, nil
+}
+
+func (f *openMapFile) Seek(offset int64, whence int) (int64, error) {
+	switch whence {
+	case 0:
+		// offset += 0
+	case 1:
+		offset += f.offset
+	case 2:
+		offset += int64(len(f.f.Data))
+	}
+	if offset < 0 || offset > int64(len(f.f.Data)) {
+		return 0, &fs.PathError{Op: "seek", Path: f.path, Err: fs.ErrInvalid}
+	}
+	f.offset = offset
+	return offset, nil
+}
+
+func (f *openMapFile) ReadAt(b []byte, offset int64) (int, error) {
+	if offset < 0 || offset > int64(len(f.f.Data)) {
+		return 0, &fs.PathError{Op: "read", Path: f.path, Err: fs.ErrInvalid}
+	}
+	n := copy(b, f.f.Data[offset:])
+	if n < len(b) {
+		return n, io.EOF
+	}
+	return n, nil
+}
+
+// A mapDir is a directory fs.File (so also an fs.ReadDirFile) open for reading.
+type mapDir struct {
+	path string
+	mapFileInfo
+	entry  []mapFileInfo
+	offset int
+}
+
+func (d *mapDir) Stat() (fs.FileInfo, error) { return &d.mapFileInfo, nil }
+func (d *mapDir) Close() error               { return nil }
+func (d *mapDir) Read(b []byte) (int, error) {
+	return 0, &fs.PathError{Op: "read", Path: d.path, Err: fs.ErrInvalid}
+}
+
+func (d *mapDir) ReadDir(count int) ([]fs.DirEntry, error) {
+	n := len(d.entry) - d.offset
+	if count > 0 && n > count {
+		n = count
+	}
+	if n == 0 && count > 0 {
+		return nil, io.EOF
+	}
+	list := make([]fs.DirEntry, n)
+	for i := range list {
+		list[i] = &d.entry[d.offset+i]
+	}
+	d.offset += n
+	return list, nil
+}
diff --git a/src/testing/fstest/mapfs_test.go b/src/testing/fstest/mapfs_test.go
new file mode 100644
index 0000000..2abedd6
--- /dev/null
+++ b/src/testing/fstest/mapfs_test.go
@@ -0,0 +1,19 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package fstest
+
+import (
+	"testing"
+)
+
+func TestMapFS(t *testing.T) {
+	m := MapFS{
+		"hello":             {Data: []byte("hello, world\n")},
+		"fortune/k/ken.txt": {Data: []byte("If a program is too slow, it must have a loop.\n")},
+	}
+	if err := TestFS(m, "hello", "fortune/k/ken.txt"); err != nil {
+		t.Fatal(err)
+	}
+}
diff --git a/src/testing/fstest/testfs.go b/src/testing/fstest/testfs.go
new file mode 100644
index 0000000..8fc8aca
--- /dev/null
+++ b/src/testing/fstest/testfs.go
@@ -0,0 +1,614 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package fstest implements support for testing implementations and users of file systems.
+package fstest
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"io/ioutil"
+	"path"
+	"reflect"
+	"sort"
+	"strings"
+	"testing/iotest"
+)
+
+// TestFS tests a file system implementation.
+// It walks the entire tree of files in fsys,
+// opening and checking that each file behaves correctly.
+// It also checks that the file system contains at least the expected files.
+// As a special case, if no expected files are listed, fsys must be empty.
+// Otherwise, fsys must only contain at least the listed files: it can also contain others.
+// The contents of fsys must not change concurrently with TestFS.
+//
+// If TestFS finds any misbehaviors, it returns an error reporting all of them.
+// The error text spans multiple lines, one per detected misbehavior.
+//
+// Typical usage inside a test is:
+//
+//	if err := fstest.TestFS(myFS, "file/that/should/be/present"); err != nil {
+//		t.Fatal(err)
+//	}
+//
+func TestFS(fsys fs.FS, expected ...string) error {
+	if err := testFS(fsys, expected...); err != nil {
+		return err
+	}
+	for _, name := range expected {
+		if i := strings.Index(name, "/"); i >= 0 {
+			dir, dirSlash := name[:i], name[:i+1]
+			var subExpected []string
+			for _, name := range expected {
+				if strings.HasPrefix(name, dirSlash) {
+					subExpected = append(subExpected, name[len(dirSlash):])
+				}
+			}
+			sub, err := fs.Sub(fsys, dir)
+			if err != nil {
+				return err
+			}
+			if err := testFS(sub, subExpected...); err != nil {
+				return fmt.Errorf("testing fs.Sub(fsys, %s): %v", dir, err)
+			}
+			break // one sub-test is enough
+		}
+	}
+	return nil
+}
+
+func testFS(fsys fs.FS, expected ...string) error {
+	t := fsTester{fsys: fsys}
+	t.checkDir(".")
+	t.checkOpen(".")
+	found := make(map[string]bool)
+	for _, dir := range t.dirs {
+		found[dir] = true
+	}
+	for _, file := range t.files {
+		found[file] = true
+	}
+	delete(found, ".")
+	if len(expected) == 0 && len(found) > 0 {
+		var list []string
+		for k := range found {
+			if k != "." {
+				list = append(list, k)
+			}
+		}
+		sort.Strings(list)
+		if len(list) > 15 {
+			list = append(list[:10], "...")
+		}
+		t.errorf("expected empty file system but found files:\n%s", strings.Join(list, "\n"))
+	}
+	for _, name := range expected {
+		if !found[name] {
+			t.errorf("expected but not found: %s", name)
+		}
+	}
+	if len(t.errText) == 0 {
+		return nil
+	}
+	return errors.New("TestFS found errors:\n" + string(t.errText))
+}
+
+// An fsTester holds state for running the test.
+type fsTester struct {
+	fsys    fs.FS
+	errText []byte
+	dirs    []string
+	files   []string
+}
+
+// errorf adds an error line to errText.
+func (t *fsTester) errorf(format string, args ...interface{}) {
+	if len(t.errText) > 0 {
+		t.errText = append(t.errText, '\n')
+	}
+	t.errText = append(t.errText, fmt.Sprintf(format, args...)...)
+}
+
+func (t *fsTester) openDir(dir string) fs.ReadDirFile {
+	f, err := t.fsys.Open(dir)
+	if err != nil {
+		t.errorf("%s: Open: %v", dir, err)
+		return nil
+	}
+	d, ok := f.(fs.ReadDirFile)
+	if !ok {
+		f.Close()
+		t.errorf("%s: Open returned File type %T, not a fs.ReadDirFile", dir, f)
+		return nil
+	}
+	return d
+}
+
+// checkDir checks the directory dir, which is expected to exist
+// (it is either the root or was found in a directory listing with IsDir true).
+func (t *fsTester) checkDir(dir string) {
+	// Read entire directory.
+	t.dirs = append(t.dirs, dir)
+	d := t.openDir(dir)
+	if d == nil {
+		return
+	}
+	list, err := d.ReadDir(-1)
+	if err != nil {
+		d.Close()
+		t.errorf("%s: ReadDir(-1): %v", dir, err)
+		return
+	}
+
+	// Check all children.
+	var prefix string
+	if dir == "." {
+		prefix = ""
+	} else {
+		prefix = dir + "/"
+	}
+	for _, info := range list {
+		name := info.Name()
+		switch {
+		case name == ".", name == "..", name == "":
+			t.errorf("%s: ReadDir: child has invalid name: %#q", dir, name)
+			continue
+		case strings.Contains(name, "/"):
+			t.errorf("%s: ReadDir: child name contains slash: %#q", dir, name)
+			continue
+		case strings.Contains(name, `\`):
+			t.errorf("%s: ReadDir: child name contains backslash: %#q", dir, name)
+			continue
+		}
+		path := prefix + name
+		t.checkStat(path, info)
+		t.checkOpen(path)
+		if info.IsDir() {
+			t.checkDir(path)
+		} else {
+			t.checkFile(path)
+		}
+	}
+
+	// Check ReadDir(-1) at EOF.
+	list2, err := d.ReadDir(-1)
+	if len(list2) > 0 || err != nil {
+		d.Close()
+		t.errorf("%s: ReadDir(-1) at EOF = %d entries, %v, wanted 0 entries, nil", dir, len(list2), err)
+		return
+	}
+
+	// Check ReadDir(1) at EOF (different results).
+	list2, err = d.ReadDir(1)
+	if len(list2) > 0 || err != io.EOF {
+		d.Close()
+		t.errorf("%s: ReadDir(1) at EOF = %d entries, %v, wanted 0 entries, EOF", dir, len(list2), err)
+		return
+	}
+
+	// Check that close does not report an error.
+	if err := d.Close(); err != nil {
+		t.errorf("%s: Close: %v", dir, err)
+	}
+
+	// Check that closing twice doesn't crash.
+	// The return value doesn't matter.
+	d.Close()
+
+	// Reopen directory, read a second time, make sure contents match.
+	if d = t.openDir(dir); d == nil {
+		return
+	}
+	defer d.Close()
+	list2, err = d.ReadDir(-1)
+	if err != nil {
+		t.errorf("%s: second Open+ReadDir(-1): %v", dir, err)
+		return
+	}
+	t.checkDirList(dir, "first Open+ReadDir(-1) vs second Open+ReadDir(-1)", list, list2)
+
+	// Reopen directory, read a third time in pieces, make sure contents match.
+	if d = t.openDir(dir); d == nil {
+		return
+	}
+	defer d.Close()
+	list2 = nil
+	for {
+		n := 1
+		if len(list2) > 0 {
+			n = 2
+		}
+		frag, err := d.ReadDir(n)
+		if len(frag) > n {
+			t.errorf("%s: third Open: ReadDir(%d) after %d: %d entries (too many)", dir, n, len(list2), len(frag))
+			return
+		}
+		list2 = append(list2, frag...)
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			t.errorf("%s: third Open: ReadDir(%d) after %d: %v", dir, n, len(list2), err)
+			return
+		}
+		if n == 0 {
+			t.errorf("%s: third Open: ReadDir(%d) after %d: 0 entries but nil error", dir, n, len(list2))
+			return
+		}
+	}
+	t.checkDirList(dir, "first Open+ReadDir(-1) vs third Open+ReadDir(1,2) loop", list, list2)
+
+	// If fsys has ReadDir, check that it matches and is sorted.
+	if fsys, ok := t.fsys.(fs.ReadDirFS); ok {
+		list2, err := fsys.ReadDir(dir)
+		if err != nil {
+			t.errorf("%s: fsys.ReadDir: %v", dir, err)
+			return
+		}
+		t.checkDirList(dir, "first Open+ReadDir(-1) vs fsys.ReadDir", list, list2)
+
+		for i := 0; i+1 < len(list2); i++ {
+			if list2[i].Name() >= list2[i+1].Name() {
+				t.errorf("%s: fsys.ReadDir: list not sorted: %s before %s", dir, list2[i].Name(), list2[i+1].Name())
+			}
+		}
+	}
+
+	// Check fs.ReadDir as well.
+	list2, err = fs.ReadDir(t.fsys, dir)
+	if err != nil {
+		t.errorf("%s: fs.ReadDir: %v", dir, err)
+		return
+	}
+	t.checkDirList(dir, "first Open+ReadDir(-1) vs fs.ReadDir", list, list2)
+
+	for i := 0; i+1 < len(list2); i++ {
+		if list2[i].Name() >= list2[i+1].Name() {
+			t.errorf("%s: fs.ReadDir: list not sorted: %s before %s", dir, list2[i].Name(), list2[i+1].Name())
+		}
+	}
+
+	t.checkGlob(dir, list)
+}
+
+// formatEntry formats an fs.DirEntry into a string for error messages and comparison.
+func formatEntry(entry fs.DirEntry) string {
+	return fmt.Sprintf("%s IsDir=%v Type=%v", entry.Name(), entry.IsDir(), entry.Type())
+}
+
+// formatInfoEntry formats an fs.FileInfo into a string like the result of formatEntry, for error messages and comparison.
+func formatInfoEntry(info fs.FileInfo) string {
+	return fmt.Sprintf("%s IsDir=%v Type=%v", info.Name(), info.IsDir(), info.Mode().Type())
+}
+
+// formatInfo formats an fs.FileInfo into a string for error messages and comparison.
+func formatInfo(info fs.FileInfo) string {
+	return fmt.Sprintf("%s IsDir=%v Mode=%v Size=%d ModTime=%v", info.Name(), info.IsDir(), info.Mode(), info.Size(), info.ModTime())
+}
+
+// checkGlob checks that various glob patterns work if the file system implements GlobFS.
+func (t *fsTester) checkGlob(dir string, list []fs.DirEntry) {
+	if _, ok := t.fsys.(fs.GlobFS); !ok {
+		return
+	}
+
+	// Make a complex glob pattern prefix that only matches dir.
+	var glob string
+	if dir != "." {
+		elem := strings.Split(dir, "/")
+		for i, e := range elem {
+			var pattern []rune
+			for j, r := range e {
+				if r == '*' || r == '?' || r == '\\' || r == '[' {
+					pattern = append(pattern, '\\', r)
+					continue
+				}
+				switch (i + j) % 5 {
+				case 0:
+					pattern = append(pattern, r)
+				case 1:
+					pattern = append(pattern, '[', r, ']')
+				case 2:
+					pattern = append(pattern, '[', r, '-', r, ']')
+				case 3:
+					pattern = append(pattern, '[', '\\', r, ']')
+				case 4:
+					pattern = append(pattern, '[', '\\', r, '-', '\\', r, ']')
+				}
+			}
+			elem[i] = string(pattern)
+		}
+		glob = strings.Join(elem, "/") + "/"
+	}
+
+	// Test that malformed patterns are detected.
+	// The error is likely path.ErrBadPattern but need not be.
+	if _, err := t.fsys.(fs.GlobFS).Glob(glob + "nonexist/[]"); err == nil {
+		t.errorf("%s: Glob(%#q): bad pattern not detected", dir, glob+"nonexist/[]")
+	}
+
+	// Try to find a letter that appears in only some of the final names.
+	c := rune('a')
+	for ; c <= 'z'; c++ {
+		have, haveNot := false, false
+		for _, d := range list {
+			if strings.ContainsRune(d.Name(), c) {
+				have = true
+			} else {
+				haveNot = true
+			}
+		}
+		if have && haveNot {
+			break
+		}
+	}
+	if c > 'z' {
+		c = 'a'
+	}
+	glob += "*" + string(c) + "*"
+
+	var want []string
+	for _, d := range list {
+		if strings.ContainsRune(d.Name(), c) {
+			want = append(want, path.Join(dir, d.Name()))
+		}
+	}
+
+	names, err := t.fsys.(fs.GlobFS).Glob(glob)
+	if err != nil {
+		t.errorf("%s: Glob(%#q): %v", dir, glob, err)
+		return
+	}
+	if reflect.DeepEqual(want, names) {
+		return
+	}
+
+	if !sort.StringsAreSorted(names) {
+		t.errorf("%s: Glob(%#q): unsorted output:\n%s", dir, glob, strings.Join(names, "\n"))
+		sort.Strings(names)
+	}
+
+	var problems []string
+	for len(want) > 0 || len(names) > 0 {
+		switch {
+		case len(want) > 0 && len(names) > 0 && want[0] == names[0]:
+			want, names = want[1:], names[1:]
+		case len(want) > 0 && (len(names) == 0 || want[0] < names[0]):
+			problems = append(problems, "missing: "+want[0])
+			want = want[1:]
+		default:
+			problems = append(problems, "extra: "+names[0])
+			names = names[1:]
+		}
+	}
+	t.errorf("%s: Glob(%#q): wrong output:\n%s", dir, glob, strings.Join(problems, "\n"))
+}
+
+// checkStat checks that a direct stat of path matches entry,
+// which was found in the parent's directory listing.
+func (t *fsTester) checkStat(path string, entry fs.DirEntry) {
+	file, err := t.fsys.Open(path)
+	if err != nil {
+		t.errorf("%s: Open: %v", path, err)
+		return
+	}
+	info, err := file.Stat()
+	file.Close()
+	if err != nil {
+		t.errorf("%s: Stat: %v", path, err)
+		return
+	}
+	fentry := formatEntry(entry)
+	fientry := formatInfoEntry(info)
+	// Note: mismatch here is OK for symlink, because Open dereferences symlink.
+	if fentry != fientry && entry.Type()&fs.ModeSymlink == 0 {
+		t.errorf("%s: mismatch:\n\tentry = %s\n\tfile.Stat() = %s", path, fentry, fientry)
+	}
+
+	einfo, err := entry.Info()
+	if err != nil {
+		t.errorf("%s: entry.Info: %v", path, err)
+		return
+	}
+	finfo := formatInfo(info)
+	if entry.Type()&fs.ModeSymlink != 0 {
+		// For symlink, just check that entry.Info matches entry on common fields.
+		// Open deferences symlink, so info itself may differ.
+		feentry := formatInfoEntry(einfo)
+		if fentry != feentry {
+			t.errorf("%s: mismatch\n\tentry = %s\n\tentry.Info() = %s\n", path, fentry, feentry)
+		}
+	} else {
+		feinfo := formatInfo(einfo)
+		if feinfo != finfo {
+			t.errorf("%s: mismatch:\n\tentry.Info() = %s\n\tfile.Stat() = %s\n", path, feinfo, finfo)
+		}
+	}
+
+	// Stat should be the same as Open+Stat, even for symlinks.
+	info2, err := fs.Stat(t.fsys, path)
+	if err != nil {
+		t.errorf("%s: fs.Stat: %v", path, err)
+		return
+	}
+	finfo2 := formatInfo(info2)
+	if finfo2 != finfo {
+		t.errorf("%s: fs.Stat(...) = %s\n\twant %s", path, finfo2, finfo)
+	}
+
+	if fsys, ok := t.fsys.(fs.StatFS); ok {
+		info2, err := fsys.Stat(path)
+		if err != nil {
+			t.errorf("%s: fsys.Stat: %v", path, err)
+			return
+		}
+		finfo2 := formatInfo(info2)
+		if finfo2 != finfo {
+			t.errorf("%s: fsys.Stat(...) = %s\n\twant %s", path, finfo2, finfo)
+		}
+	}
+}
+
+// checkDirList checks that two directory lists contain the same files and file info.
+// The order of the lists need not match.
+func (t *fsTester) checkDirList(dir, desc string, list1, list2 []fs.DirEntry) {
+	old := make(map[string]fs.DirEntry)
+	checkMode := func(entry fs.DirEntry) {
+		if entry.IsDir() != (entry.Type()&fs.ModeDir != 0) {
+			if entry.IsDir() {
+				t.errorf("%s: ReadDir returned %s with IsDir() = true, Type() & ModeDir = 0", dir, entry.Name())
+			} else {
+				t.errorf("%s: ReadDir returned %s with IsDir() = false, Type() & ModeDir = ModeDir", dir, entry.Name())
+			}
+		}
+	}
+
+	for _, entry1 := range list1 {
+		old[entry1.Name()] = entry1
+		checkMode(entry1)
+	}
+
+	var diffs []string
+	for _, entry2 := range list2 {
+		entry1 := old[entry2.Name()]
+		if entry1 == nil {
+			checkMode(entry2)
+			diffs = append(diffs, "+ "+formatEntry(entry2))
+			continue
+		}
+		if formatEntry(entry1) != formatEntry(entry2) {
+			diffs = append(diffs, "- "+formatEntry(entry1), "+ "+formatEntry(entry2))
+		}
+		delete(old, entry2.Name())
+	}
+	for _, entry1 := range old {
+		diffs = append(diffs, "- "+formatEntry(entry1))
+	}
+
+	if len(diffs) == 0 {
+		return
+	}
+
+	sort.Slice(diffs, func(i, j int) bool {
+		fi := strings.Fields(diffs[i])
+		fj := strings.Fields(diffs[j])
+		// sort by name (i < j) and then +/- (j < i, because + < -)
+		return fi[1]+" "+fj[0] < fj[1]+" "+fi[0]
+	})
+
+	t.errorf("%s: diff %s:\n\t%s", dir, desc, strings.Join(diffs, "\n\t"))
+}
+
+// checkFile checks that basic file reading works correctly.
+func (t *fsTester) checkFile(file string) {
+	t.files = append(t.files, file)
+
+	// Read entire file.
+	f, err := t.fsys.Open(file)
+	if err != nil {
+		t.errorf("%s: Open: %v", file, err)
+		return
+	}
+
+	data, err := ioutil.ReadAll(f)
+	if err != nil {
+		f.Close()
+		t.errorf("%s: Open+ReadAll: %v", file, err)
+		return
+	}
+
+	if err := f.Close(); err != nil {
+		t.errorf("%s: Close: %v", file, err)
+	}
+
+	// Check that closing twice doesn't crash.
+	// The return value doesn't matter.
+	f.Close()
+
+	// Check that ReadFile works if present.
+	if fsys, ok := t.fsys.(fs.ReadFileFS); ok {
+		data2, err := fsys.ReadFile(file)
+		if err != nil {
+			t.errorf("%s: fsys.ReadFile: %v", file, err)
+			return
+		}
+		t.checkFileRead(file, "ReadAll vs fsys.ReadFile", data, data2)
+
+		t.checkBadPath(file, "ReadFile",
+			func(name string) error { _, err := fsys.ReadFile(name); return err })
+	}
+
+	// Check that fs.ReadFile works with t.fsys.
+	data2, err := fs.ReadFile(t.fsys, file)
+	if err != nil {
+		t.errorf("%s: fs.ReadFile: %v", file, err)
+		return
+	}
+	t.checkFileRead(file, "ReadAll vs fs.ReadFile", data, data2)
+
+	// Use iotest.TestReader to check small reads, Seek, ReadAt.
+	f, err = t.fsys.Open(file)
+	if err != nil {
+		t.errorf("%s: second Open: %v", file, err)
+		return
+	}
+	defer f.Close()
+	if err := iotest.TestReader(f, data); err != nil {
+		t.errorf("%s: failed TestReader:\n\t%s", file, strings.ReplaceAll(err.Error(), "\n", "\n\t"))
+	}
+}
+
+func (t *fsTester) checkFileRead(file, desc string, data1, data2 []byte) {
+	if string(data1) != string(data2) {
+		t.errorf("%s: %s: different data returned\n\t%q\n\t%q", file, desc, data1, data2)
+		return
+	}
+}
+
+// checkBadPath checks that various invalid forms of file's name cannot be opened using t.fsys.Open.
+func (t *fsTester) checkOpen(file string) {
+	t.checkBadPath(file, "Open", func(file string) error {
+		f, err := t.fsys.Open(file)
+		if err == nil {
+			f.Close()
+		}
+		return err
+	})
+}
+
+// checkBadPath checks that various invalid forms of file's name cannot be opened using open.
+func (t *fsTester) checkBadPath(file string, desc string, open func(string) error) {
+	bad := []string{
+		"/" + file,
+		file + "/.",
+	}
+	if file == "." {
+		bad = append(bad, "/")
+	}
+	if i := strings.Index(file, "/"); i >= 0 {
+		bad = append(bad,
+			file[:i]+"//"+file[i+1:],
+			file[:i]+"/./"+file[i+1:],
+			file[:i]+`\`+file[i+1:],
+			file[:i]+"/../"+file,
+		)
+	}
+	if i := strings.LastIndex(file, "/"); i >= 0 {
+		bad = append(bad,
+			file[:i]+"//"+file[i+1:],
+			file[:i]+"/./"+file[i+1:],
+			file[:i]+`\`+file[i+1:],
+			file+"/../"+file[i+1:],
+		)
+	}
+
+	for _, b := range bad {
+		if err := open(b); err == nil {
+			t.errorf("%s: %s(%s) succeeded, want error", file, desc, b)
+		}
+	}
+}
diff --git a/src/testing/fstest/testfs_test.go b/src/testing/fstest/testfs_test.go
new file mode 100644
index 0000000..5b8813c
--- /dev/null
+++ b/src/testing/fstest/testfs_test.go
@@ -0,0 +1,31 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package fstest
+
+import (
+	"internal/testenv"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestSymlink(t *testing.T) {
+	testenv.MustHaveSymlink(t)
+
+	tmp := t.TempDir()
+	tmpfs := os.DirFS(tmp)
+
+	if err := os.WriteFile(filepath.Join(tmp, "hello"), []byte("hello, world\n"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := os.Symlink(filepath.Join(tmp, "hello"), filepath.Join(tmp, "hello.link")); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := TestFS(tmpfs, "hello", "hello.link"); err != nil {
+		t.Fatal(err)
+	}
+}
diff --git a/src/testing/helper_test.go b/src/testing/helper_test.go
new file mode 100644
index 0000000..b27fd62
--- /dev/null
+++ b/src/testing/helper_test.go
@@ -0,0 +1,135 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testing
+
+import (
+	"bytes"
+	"regexp"
+	"strings"
+)
+
+func TestTBHelper(t *T) {
+	var buf bytes.Buffer
+	ctx := newTestContext(1, newMatcher(regexp.MatchString, "", ""))
+	t1 := &T{
+		common: common{
+			signal: make(chan bool),
+			w:      &buf,
+		},
+		context: ctx,
+	}
+	t1.Run("Test", testHelper)
+
+	want := `--- FAIL: Test (?s)
+helperfuncs_test.go:12: 0
+helperfuncs_test.go:33: 1
+helperfuncs_test.go:21: 2
+helperfuncs_test.go:35: 3
+helperfuncs_test.go:42: 4
+--- FAIL: Test/sub (?s)
+helperfuncs_test.go:45: 5
+helperfuncs_test.go:21: 6
+helperfuncs_test.go:44: 7
+helperfuncs_test.go:56: 8
+helperfuncs_test.go:64: 9
+helperfuncs_test.go:60: 10
+`
+	lines := strings.Split(buf.String(), "\n")
+	durationRE := regexp.MustCompile(`\(.*\)$`)
+	for i, line := range lines {
+		line = strings.TrimSpace(line)
+		line = durationRE.ReplaceAllString(line, "(?s)")
+		lines[i] = line
+	}
+	got := strings.Join(lines, "\n")
+	if got != want {
+		t.Errorf("got output:\n\n%s\nwant:\n\n%s", got, want)
+	}
+}
+
+func TestTBHelperParallel(t *T) {
+	var buf bytes.Buffer
+	ctx := newTestContext(1, newMatcher(regexp.MatchString, "", ""))
+	t1 := &T{
+		common: common{
+			signal: make(chan bool),
+			w:      &buf,
+		},
+		context: ctx,
+	}
+	t1.Run("Test", parallelTestHelper)
+
+	lines := strings.Split(strings.TrimSpace(buf.String()), "\n")
+	if len(lines) != 6 {
+		t.Fatalf("parallelTestHelper gave %d lines of output; want 6", len(lines))
+	}
+	want := "helperfuncs_test.go:21: parallel"
+	if got := strings.TrimSpace(lines[1]); got != want {
+		t.Errorf("got output line %q; want %q", got, want)
+	}
+}
+
+func TestTBHelperLineNumer(t *T) {
+	var buf bytes.Buffer
+	ctx := newTestContext(1, newMatcher(regexp.MatchString, "", ""))
+	t1 := &T{
+		common: common{
+			signal: make(chan bool),
+			w:      &buf,
+		},
+		context: ctx,
+	}
+	t1.Run("Test", func(t *T) {
+		helperA := func(t *T) {
+			t.Helper()
+			t.Run("subtest", func(t *T) {
+				t.Helper()
+				t.Fatal("fatal error message")
+			})
+		}
+		helperA(t)
+	})
+
+	want := "helper_test.go:92: fatal error message"
+	got := ""
+	lines := strings.Split(strings.TrimSpace(buf.String()), "\n")
+	if len(lines) > 0 {
+		got = strings.TrimSpace(lines[len(lines)-1])
+	}
+	if got != want {
+		t.Errorf("got output:\n\n%v\nwant:\n\n%v", got, want)
+	}
+}
+
+type noopWriter int
+
+func (nw *noopWriter) Write(b []byte) (int, error) { return len(b), nil }
+
+func BenchmarkTBHelper(b *B) {
+	w := noopWriter(0)
+	ctx := newTestContext(1, newMatcher(regexp.MatchString, "", ""))
+	t1 := &T{
+		common: common{
+			signal: make(chan bool),
+			w:      &w,
+		},
+		context: ctx,
+	}
+	f1 := func() {
+		t1.Helper()
+	}
+	f2 := func() {
+		t1.Helper()
+	}
+	b.ResetTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		if i&1 == 0 {
+			f1()
+		} else {
+			f2()
+		}
+	}
+}
diff --git a/src/testing/helperfuncs_test.go b/src/testing/helperfuncs_test.go
new file mode 100644
index 0000000..df0476e
--- /dev/null
+++ b/src/testing/helperfuncs_test.go
@@ -0,0 +1,80 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testing
+
+import "sync"
+
+// The line numbering of this file is important for TestTBHelper.
+
+func notHelper(t *T, msg string) {
+	t.Error(msg)
+}
+
+func helper(t *T, msg string) {
+	t.Helper()
+	t.Error(msg)
+}
+
+func notHelperCallingHelper(t *T, msg string) {
+	helper(t, msg)
+}
+
+func helperCallingHelper(t *T, msg string) {
+	t.Helper()
+	helper(t, msg)
+}
+
+func testHelper(t *T) {
+	// Check combinations of directly and indirectly
+	// calling helper functions.
+	notHelper(t, "0")
+	helper(t, "1")
+	notHelperCallingHelper(t, "2")
+	helperCallingHelper(t, "3")
+
+	// Check a function literal closing over t that uses Helper.
+	fn := func(msg string) {
+		t.Helper()
+		t.Error(msg)
+	}
+	fn("4")
+
+	t.Run("sub", func(t *T) {
+		helper(t, "5")
+		notHelperCallingHelper(t, "6")
+		// Check that calling Helper from inside a subtest entry function
+		// works as if it were in an ordinary function call.
+		t.Helper()
+		t.Error("7")
+	})
+
+	// Check that calling Helper from inside a top-level test function
+	// has no effect.
+	t.Helper()
+	t.Error("8")
+
+	// Check that right caller is reported for func passed to Cleanup when
+	// multiple cleanup functions have been registered.
+	t.Cleanup(func() {
+		t.Helper()
+		t.Error("10")
+	})
+	t.Cleanup(func() {
+		t.Helper()
+		t.Error("9")
+	})
+}
+
+func parallelTestHelper(t *T) {
+	var wg sync.WaitGroup
+	for i := 0; i < 5; i++ {
+		wg.Add(1)
+		go func() {
+			notHelperCallingHelper(t, "parallel")
+			wg.Done()
+		}()
+	}
+	wg.Wait()
+}
diff --git a/src/testing/internal/testdeps/deps.go b/src/testing/internal/testdeps/deps.go
new file mode 100644
index 0000000..3608d33
--- /dev/null
+++ b/src/testing/internal/testdeps/deps.go
@@ -0,0 +1,128 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package testdeps provides access to dependencies needed by test execution.
+//
+// This package is imported by the generated main package, which passes
+// TestDeps into testing.Main. This allows tests to use packages at run time
+// without making those packages direct dependencies of package testing.
+// Direct dependencies of package testing are harder to write tests for.
+package testdeps
+
+import (
+	"bufio"
+	"internal/testlog"
+	"io"
+	"regexp"
+	"runtime/pprof"
+	"strings"
+	"sync"
+)
+
+// TestDeps is an implementation of the testing.testDeps interface,
+// suitable for passing to testing.MainStart.
+type TestDeps struct{}
+
+var matchPat string
+var matchRe *regexp.Regexp
+
+func (TestDeps) MatchString(pat, str string) (result bool, err error) {
+	if matchRe == nil || matchPat != pat {
+		matchPat = pat
+		matchRe, err = regexp.Compile(matchPat)
+		if err != nil {
+			return
+		}
+	}
+	return matchRe.MatchString(str), nil
+}
+
+func (TestDeps) StartCPUProfile(w io.Writer) error {
+	return pprof.StartCPUProfile(w)
+}
+
+func (TestDeps) StopCPUProfile() {
+	pprof.StopCPUProfile()
+}
+
+func (TestDeps) WriteProfileTo(name string, w io.Writer, debug int) error {
+	return pprof.Lookup(name).WriteTo(w, debug)
+}
+
+// ImportPath is the import path of the testing binary, set by the generated main function.
+var ImportPath string
+
+func (TestDeps) ImportPath() string {
+	return ImportPath
+}
+
+// testLog implements testlog.Interface, logging actions by package os.
+type testLog struct {
+	mu  sync.Mutex
+	w   *bufio.Writer
+	set bool
+}
+
+func (l *testLog) Getenv(key string) {
+	l.add("getenv", key)
+}
+
+func (l *testLog) Open(name string) {
+	l.add("open", name)
+}
+
+func (l *testLog) Stat(name string) {
+	l.add("stat", name)
+}
+
+func (l *testLog) Chdir(name string) {
+	l.add("chdir", name)
+}
+
+// add adds the (op, name) pair to the test log.
+func (l *testLog) add(op, name string) {
+	if strings.Contains(name, "\n") || name == "" {
+		return
+	}
+
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	if l.w == nil {
+		return
+	}
+	l.w.WriteString(op)
+	l.w.WriteByte(' ')
+	l.w.WriteString(name)
+	l.w.WriteByte('\n')
+}
+
+var log testLog
+
+func (TestDeps) StartTestLog(w io.Writer) {
+	log.mu.Lock()
+	log.w = bufio.NewWriter(w)
+	if !log.set {
+		// Tests that define TestMain and then run m.Run multiple times
+		// will call StartTestLog/StopTestLog multiple times.
+		// Checking log.set avoids calling testlog.SetLogger multiple times
+		// (which will panic) and also avoids writing the header multiple times.
+		log.set = true
+		testlog.SetLogger(&log)
+		log.w.WriteString("# test log\n") // known to cmd/go/internal/test/test.go
+	}
+	log.mu.Unlock()
+}
+
+func (TestDeps) StopTestLog() error {
+	log.mu.Lock()
+	defer log.mu.Unlock()
+	err := log.w.Flush()
+	log.w = nil
+	return err
+}
+
+// SetPanicOnExit0 tells the os package whether to panic on os.Exit(0).
+func (TestDeps) SetPanicOnExit0(v bool) {
+	testlog.SetPanicOnExit0(v)
+}
diff --git a/src/testing/iotest/example_test.go b/src/testing/iotest/example_test.go
new file mode 100644
index 0000000..10f6bd3
--- /dev/null
+++ b/src/testing/iotest/example_test.go
@@ -0,0 +1,22 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package iotest_test
+
+import (
+	"errors"
+	"fmt"
+	"testing/iotest"
+)
+
+func ExampleErrReader() {
+	// A reader that always returns a custom error.
+	r := iotest.ErrReader(errors.New("custom error"))
+	n, err := r.Read(nil)
+	fmt.Printf("n:   %d\nerr: %q\n", n, err)
+
+	// Output:
+	// n:   0
+	// err: "custom error"
+}
diff --git a/src/testing/iotest/logger.go b/src/testing/iotest/logger.go
new file mode 100644
index 0000000..99548dc
--- /dev/null
+++ b/src/testing/iotest/logger.go
@@ -0,0 +1,54 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package iotest
+
+import (
+	"io"
+	"log"
+)
+
+type writeLogger struct {
+	prefix string
+	w      io.Writer
+}
+
+func (l *writeLogger) Write(p []byte) (n int, err error) {
+	n, err = l.w.Write(p)
+	if err != nil {
+		log.Printf("%s %x: %v", l.prefix, p[0:n], err)
+	} else {
+		log.Printf("%s %x", l.prefix, p[0:n])
+	}
+	return
+}
+
+// NewWriteLogger returns a writer that behaves like w except
+// that it logs (using log.Printf) each write to standard error,
+// printing the prefix and the hexadecimal data written.
+func NewWriteLogger(prefix string, w io.Writer) io.Writer {
+	return &writeLogger{prefix, w}
+}
+
+type readLogger struct {
+	prefix string
+	r      io.Reader
+}
+
+func (l *readLogger) Read(p []byte) (n int, err error) {
+	n, err = l.r.Read(p)
+	if err != nil {
+		log.Printf("%s %x: %v", l.prefix, p[0:n], err)
+	} else {
+		log.Printf("%s %x", l.prefix, p[0:n])
+	}
+	return
+}
+
+// NewReadLogger returns a reader that behaves like r except
+// that it logs (using log.Printf) each read to standard error,
+// printing the prefix and the hexadecimal data read.
+func NewReadLogger(prefix string, r io.Reader) io.Reader {
+	return &readLogger{prefix, r}
+}
diff --git a/src/testing/iotest/logger_test.go b/src/testing/iotest/logger_test.go
new file mode 100644
index 0000000..fec4467
--- /dev/null
+++ b/src/testing/iotest/logger_test.go
@@ -0,0 +1,152 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package iotest
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"log"
+	"testing"
+)
+
+type errWriter struct {
+	err error
+}
+
+func (w errWriter) Write([]byte) (int, error) {
+	return 0, w.err
+}
+
+func TestWriteLogger(t *testing.T) {
+	olw := log.Writer()
+	olf := log.Flags()
+	olp := log.Prefix()
+
+	// Revert the original log settings before we exit.
+	defer func() {
+		log.SetFlags(olf)
+		log.SetPrefix(olp)
+		log.SetOutput(olw)
+	}()
+
+	lOut := new(bytes.Buffer)
+	log.SetPrefix("lw: ")
+	log.SetOutput(lOut)
+	log.SetFlags(0)
+
+	lw := new(bytes.Buffer)
+	wl := NewWriteLogger("write:", lw)
+	if _, err := wl.Write([]byte("Hello, World!")); err != nil {
+		t.Fatalf("Unexpectedly failed to write: %v", err)
+	}
+
+	if g, w := lw.String(), "Hello, World!"; g != w {
+		t.Errorf("WriteLogger mismatch\n\tgot:  %q\n\twant: %q", g, w)
+	}
+	wantLogWithHex := fmt.Sprintf("lw: write: %x\n", "Hello, World!")
+	if g, w := lOut.String(), wantLogWithHex; g != w {
+		t.Errorf("WriteLogger mismatch\n\tgot:  %q\n\twant: %q", g, w)
+	}
+}
+
+func TestWriteLogger_errorOnWrite(t *testing.T) {
+	olw := log.Writer()
+	olf := log.Flags()
+	olp := log.Prefix()
+
+	// Revert the original log settings before we exit.
+	defer func() {
+		log.SetFlags(olf)
+		log.SetPrefix(olp)
+		log.SetOutput(olw)
+	}()
+
+	lOut := new(bytes.Buffer)
+	log.SetPrefix("lw: ")
+	log.SetOutput(lOut)
+	log.SetFlags(0)
+
+	lw := errWriter{err: errors.New("Write Error!")}
+	wl := NewWriteLogger("write:", lw)
+	if _, err := wl.Write([]byte("Hello, World!")); err == nil {
+		t.Fatalf("Unexpectedly succeeded to write: %v", err)
+	}
+
+	wantLogWithHex := fmt.Sprintf("lw: write: %x: %v\n", "", "Write Error!")
+	if g, w := lOut.String(), wantLogWithHex; g != w {
+		t.Errorf("WriteLogger mismatch\n\tgot:  %q\n\twant: %q", g, w)
+	}
+}
+
+func TestReadLogger(t *testing.T) {
+	olw := log.Writer()
+	olf := log.Flags()
+	olp := log.Prefix()
+
+	// Revert the original log settings before we exit.
+	defer func() {
+		log.SetFlags(olf)
+		log.SetPrefix(olp)
+		log.SetOutput(olw)
+	}()
+
+	lOut := new(bytes.Buffer)
+	log.SetPrefix("lr: ")
+	log.SetOutput(lOut)
+	log.SetFlags(0)
+
+	data := []byte("Hello, World!")
+	p := make([]byte, len(data))
+	lr := bytes.NewReader(data)
+	rl := NewReadLogger("read:", lr)
+
+	n, err := rl.Read(p)
+	if err != nil {
+		t.Fatalf("Unexpectedly failed to read: %v", err)
+	}
+
+	if g, w := p[:n], data; !bytes.Equal(g, w) {
+		t.Errorf("ReadLogger mismatch\n\tgot:  %q\n\twant: %q", g, w)
+	}
+
+	wantLogWithHex := fmt.Sprintf("lr: read: %x\n", "Hello, World!")
+	if g, w := lOut.String(), wantLogWithHex; g != w {
+		t.Errorf("ReadLogger mismatch\n\tgot:  %q\n\twant: %q", g, w)
+	}
+}
+
+func TestReadLogger_errorOnRead(t *testing.T) {
+	olw := log.Writer()
+	olf := log.Flags()
+	olp := log.Prefix()
+
+	// Revert the original log settings before we exit.
+	defer func() {
+		log.SetFlags(olf)
+		log.SetPrefix(olp)
+		log.SetOutput(olw)
+	}()
+
+	lOut := new(bytes.Buffer)
+	log.SetPrefix("lr: ")
+	log.SetOutput(lOut)
+	log.SetFlags(0)
+
+	data := []byte("Hello, World!")
+	p := make([]byte, len(data))
+
+	lr := ErrReader(errors.New("io failure"))
+	rl := NewReadLogger("read", lr)
+	n, err := rl.Read(p)
+	if err == nil {
+		t.Fatalf("Unexpectedly succeeded to read: %v", err)
+	}
+
+	wantLogWithHex := fmt.Sprintf("lr: read %x: io failure\n", p[:n])
+	if g, w := lOut.String(), wantLogWithHex; g != w {
+		t.Errorf("ReadLogger mismatch\n\tgot:  %q\n\twant: %q", g, w)
+	}
+}
diff --git a/src/testing/iotest/reader.go b/src/testing/iotest/reader.go
new file mode 100644
index 0000000..770d87f
--- /dev/null
+++ b/src/testing/iotest/reader.go
@@ -0,0 +1,268 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package iotest implements Readers and Writers useful mainly for testing.
+package iotest
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+)
+
+// OneByteReader returns a Reader that implements
+// each non-empty Read by reading one byte from r.
+func OneByteReader(r io.Reader) io.Reader { return &oneByteReader{r} }
+
+type oneByteReader struct {
+	r io.Reader
+}
+
+func (r *oneByteReader) Read(p []byte) (int, error) {
+	if len(p) == 0 {
+		return 0, nil
+	}
+	return r.r.Read(p[0:1])
+}
+
+// HalfReader returns a Reader that implements Read
+// by reading half as many requested bytes from r.
+func HalfReader(r io.Reader) io.Reader { return &halfReader{r} }
+
+type halfReader struct {
+	r io.Reader
+}
+
+func (r *halfReader) Read(p []byte) (int, error) {
+	return r.r.Read(p[0 : (len(p)+1)/2])
+}
+
+// DataErrReader changes the way errors are handled by a Reader. Normally, a
+// Reader returns an error (typically EOF) from the first Read call after the
+// last piece of data is read. DataErrReader wraps a Reader and changes its
+// behavior so the final error is returned along with the final data, instead
+// of in the first call after the final data.
+func DataErrReader(r io.Reader) io.Reader { return &dataErrReader{r, nil, make([]byte, 1024)} }
+
+type dataErrReader struct {
+	r      io.Reader
+	unread []byte
+	data   []byte
+}
+
+func (r *dataErrReader) Read(p []byte) (n int, err error) {
+	// loop because first call needs two reads:
+	// one to get data and a second to look for an error.
+	for {
+		if len(r.unread) == 0 {
+			n1, err1 := r.r.Read(r.data)
+			r.unread = r.data[0:n1]
+			err = err1
+		}
+		if n > 0 || err != nil {
+			break
+		}
+		n = copy(p, r.unread)
+		r.unread = r.unread[n:]
+	}
+	return
+}
+
+// ErrTimeout is a fake timeout error.
+var ErrTimeout = errors.New("timeout")
+
+// TimeoutReader returns ErrTimeout on the second read
+// with no data. Subsequent calls to read succeed.
+func TimeoutReader(r io.Reader) io.Reader { return &timeoutReader{r, 0} }
+
+type timeoutReader struct {
+	r     io.Reader
+	count int
+}
+
+func (r *timeoutReader) Read(p []byte) (int, error) {
+	r.count++
+	if r.count == 2 {
+		return 0, ErrTimeout
+	}
+	return r.r.Read(p)
+}
+
+// ErrReader returns an io.Reader that returns 0, err from all Read calls.
+func ErrReader(err error) io.Reader {
+	return &errReader{err: err}
+}
+
+type errReader struct {
+	err error
+}
+
+func (r *errReader) Read(p []byte) (int, error) {
+	return 0, r.err
+}
+
+type smallByteReader struct {
+	r   io.Reader
+	off int
+	n   int
+}
+
+func (r *smallByteReader) Read(p []byte) (int, error) {
+	if len(p) == 0 {
+		return 0, nil
+	}
+	r.n = r.n%3 + 1
+	n := r.n
+	if n > len(p) {
+		n = len(p)
+	}
+	n, err := r.r.Read(p[0:n])
+	if err != nil && err != io.EOF {
+		err = fmt.Errorf("Read(%d bytes at offset %d): %v", n, r.off, err)
+	}
+	r.off += n
+	return n, err
+}
+
+// TestReader tests that reading from r returns the expected file content.
+// It does reads of different sizes, until EOF.
+// If r implements io.ReaderAt or io.Seeker, TestReader also checks
+// that those operations behave as they should.
+//
+// If TestReader finds any misbehaviors, it returns an error reporting them.
+// The error text may span multiple lines.
+func TestReader(r io.Reader, content []byte) error {
+	if len(content) > 0 {
+		n, err := r.Read(nil)
+		if n != 0 || err != nil {
+			return fmt.Errorf("Read(0) = %d, %v, want 0, nil", n, err)
+		}
+	}
+
+	data, err := io.ReadAll(&smallByteReader{r: r})
+	if err != nil {
+		return err
+	}
+	if !bytes.Equal(data, content) {
+		return fmt.Errorf("ReadAll(small amounts) = %q\n\twant %q", data, content)
+	}
+	n, err := r.Read(make([]byte, 10))
+	if n != 0 || err != io.EOF {
+		return fmt.Errorf("Read(10) at EOF = %v, %v, want 0, EOF", n, err)
+	}
+
+	if r, ok := r.(io.ReadSeeker); ok {
+		// Seek(0, 1) should report the current file position (EOF).
+		if off, err := r.Seek(0, 1); off != int64(len(content)) || err != nil {
+			return fmt.Errorf("Seek(0, 1) from EOF = %d, %v, want %d, nil", off, err, len(content))
+		}
+
+		// Seek backward partway through file, in two steps.
+		// If middle == 0, len(content) == 0, can't use the -1 and +1 seeks.
+		middle := len(content) - len(content)/3
+		if middle > 0 {
+			if off, err := r.Seek(-1, 1); off != int64(len(content)-1) || err != nil {
+				return fmt.Errorf("Seek(-1, 1) from EOF = %d, %v, want %d, nil", -off, err, len(content)-1)
+			}
+			if off, err := r.Seek(int64(-len(content)/3), 1); off != int64(middle-1) || err != nil {
+				return fmt.Errorf("Seek(%d, 1) from %d = %d, %v, want %d, nil", -len(content)/3, len(content)-1, off, err, middle-1)
+			}
+			if off, err := r.Seek(+1, 1); off != int64(middle) || err != nil {
+				return fmt.Errorf("Seek(+1, 1) from %d = %d, %v, want %d, nil", middle-1, off, err, middle)
+			}
+		}
+
+		// Seek(0, 1) should report the current file position (middle).
+		if off, err := r.Seek(0, 1); off != int64(middle) || err != nil {
+			return fmt.Errorf("Seek(0, 1) from %d = %d, %v, want %d, nil", middle, off, err, middle)
+		}
+
+		// Reading forward should return the last part of the file.
+		data, err := io.ReadAll(&smallByteReader{r: r})
+		if err != nil {
+			return fmt.Errorf("ReadAll from offset %d: %v", middle, err)
+		}
+		if !bytes.Equal(data, content[middle:]) {
+			return fmt.Errorf("ReadAll from offset %d = %q\n\twant %q", middle, data, content[middle:])
+		}
+
+		// Seek relative to end of file, but start elsewhere.
+		if off, err := r.Seek(int64(middle/2), 0); off != int64(middle/2) || err != nil {
+			return fmt.Errorf("Seek(%d, 0) from EOF = %d, %v, want %d, nil", middle/2, off, err, middle/2)
+		}
+		if off, err := r.Seek(int64(-len(content)/3), 2); off != int64(middle) || err != nil {
+			return fmt.Errorf("Seek(%d, 2) from %d = %d, %v, want %d, nil", -len(content)/3, middle/2, off, err, middle)
+		}
+
+		// Reading forward should return the last part of the file (again).
+		data, err = io.ReadAll(&smallByteReader{r: r})
+		if err != nil {
+			return fmt.Errorf("ReadAll from offset %d: %v", middle, err)
+		}
+		if !bytes.Equal(data, content[middle:]) {
+			return fmt.Errorf("ReadAll from offset %d = %q\n\twant %q", middle, data, content[middle:])
+		}
+
+		// Absolute seek & read forward.
+		if off, err := r.Seek(int64(middle/2), 0); off != int64(middle/2) || err != nil {
+			return fmt.Errorf("Seek(%d, 0) from EOF = %d, %v, want %d, nil", middle/2, off, err, middle/2)
+		}
+		data, err = io.ReadAll(r)
+		if err != nil {
+			return fmt.Errorf("ReadAll from offset %d: %v", middle/2, err)
+		}
+		if !bytes.Equal(data, content[middle/2:]) {
+			return fmt.Errorf("ReadAll from offset %d = %q\n\twant %q", middle/2, data, content[middle/2:])
+		}
+	}
+
+	if r, ok := r.(io.ReaderAt); ok {
+		data := make([]byte, len(content), len(content)+1)
+		for i := range data {
+			data[i] = 0xfe
+		}
+		n, err := r.ReadAt(data, 0)
+		if n != len(data) || err != nil && err != io.EOF {
+			return fmt.Errorf("ReadAt(%d, 0) = %v, %v, want %d, nil or EOF", len(data), n, err, len(data))
+		}
+		if !bytes.Equal(data, content) {
+			return fmt.Errorf("ReadAt(%d, 0) = %q\n\twant %q", len(data), data, content)
+		}
+
+		n, err = r.ReadAt(data[:1], int64(len(data)))
+		if n != 0 || err != io.EOF {
+			return fmt.Errorf("ReadAt(1, %d) = %v, %v, want 0, EOF", len(data), n, err)
+		}
+
+		for i := range data {
+			data[i] = 0xfe
+		}
+		n, err = r.ReadAt(data[:cap(data)], 0)
+		if n != len(data) || err != io.EOF {
+			return fmt.Errorf("ReadAt(%d, 0) = %v, %v, want %d, EOF", cap(data), n, err, len(data))
+		}
+		if !bytes.Equal(data, content) {
+			return fmt.Errorf("ReadAt(%d, 0) = %q\n\twant %q", len(data), data, content)
+		}
+
+		for i := range data {
+			data[i] = 0xfe
+		}
+		for i := range data {
+			n, err = r.ReadAt(data[i:i+1], int64(i))
+			if n != 1 || err != nil && (i != len(data)-1 || err != io.EOF) {
+				want := "nil"
+				if i == len(data)-1 {
+					want = "nil or EOF"
+				}
+				return fmt.Errorf("ReadAt(1, %d) = %v, %v, want 1, %s", i, n, err, want)
+			}
+			if data[i] != content[i] {
+				return fmt.Errorf("ReadAt(1, %d) = %q want %q", i, data[i:i+1], content[i:i+1])
+			}
+		}
+	}
+	return nil
+}
diff --git a/src/testing/iotest/reader_test.go b/src/testing/iotest/reader_test.go
new file mode 100644
index 0000000..f149e74
--- /dev/null
+++ b/src/testing/iotest/reader_test.go
@@ -0,0 +1,261 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package iotest
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestOneByteReader_nonEmptyReader(t *testing.T) {
+	msg := "Hello, World!"
+	buf := new(bytes.Buffer)
+	buf.WriteString(msg)
+
+	obr := OneByteReader(buf)
+	var b []byte
+	n, err := obr.Read(b)
+	if err != nil || n != 0 {
+		t.Errorf("Empty buffer read returned n=%d err=%v", n, err)
+	}
+
+	b = make([]byte, 3)
+	// Read from obr until EOF.
+	got := new(bytes.Buffer)
+	for i := 0; ; i++ {
+		n, err = obr.Read(b)
+		if err != nil {
+			break
+		}
+		if g, w := n, 1; g != w {
+			t.Errorf("Iteration #%d read %d bytes, want %d", i, g, w)
+		}
+		got.Write(b[:n])
+	}
+	if g, w := err, io.EOF; g != w {
+		t.Errorf("Unexpected error after reading all bytes\n\tGot:  %v\n\tWant: %v", g, w)
+	}
+	if g, w := got.String(), "Hello, World!"; g != w {
+		t.Errorf("Read mismatch\n\tGot:  %q\n\tWant: %q", g, w)
+	}
+}
+
+func TestOneByteReader_emptyReader(t *testing.T) {
+	r := new(bytes.Buffer)
+
+	obr := OneByteReader(r)
+	var b []byte
+	if n, err := obr.Read(b); err != nil || n != 0 {
+		t.Errorf("Empty buffer read returned n=%d err=%v", n, err)
+	}
+
+	b = make([]byte, 5)
+	n, err := obr.Read(b)
+	if g, w := err, io.EOF; g != w {
+		t.Errorf("Error mismatch\n\tGot:  %v\n\tWant: %v", g, w)
+	}
+	if g, w := n, 0; g != w {
+		t.Errorf("Unexpectedly read %d bytes, wanted %d", g, w)
+	}
+}
+
+func TestHalfReader_nonEmptyReader(t *testing.T) {
+	msg := "Hello, World!"
+	buf := new(bytes.Buffer)
+	buf.WriteString(msg)
+	// empty read buffer
+	hr := HalfReader(buf)
+	var b []byte
+	n, err := hr.Read(b)
+	if err != nil || n != 0 {
+		t.Errorf("Empty buffer read returned n=%d err=%v", n, err)
+	}
+	// non empty read buffer
+	b = make([]byte, 2)
+	got := new(bytes.Buffer)
+	for i := 0; ; i++ {
+		n, err = hr.Read(b)
+		if err != nil {
+			break
+		}
+		if g, w := n, 1; g != w {
+			t.Errorf("Iteration #%d read %d bytes, want %d", i, g, w)
+		}
+		got.Write(b[:n])
+	}
+	if g, w := err, io.EOF; g != w {
+		t.Errorf("Unexpected error after reading all bytes\n\tGot:  %v\n\tWant: %v", g, w)
+	}
+	if g, w := got.String(), "Hello, World!"; g != w {
+		t.Errorf("Read mismatch\n\tGot:  %q\n\tWant: %q", g, w)
+	}
+}
+
+func TestHalfReader_emptyReader(t *testing.T) {
+	r := new(bytes.Buffer)
+
+	hr := HalfReader(r)
+	var b []byte
+	if n, err := hr.Read(b); err != nil || n != 0 {
+		t.Errorf("Empty buffer read returned n=%d err=%v", n, err)
+	}
+
+	b = make([]byte, 5)
+	n, err := hr.Read(b)
+	if g, w := err, io.EOF; g != w {
+		t.Errorf("Error mismatch\n\tGot:  %v\n\tWant: %v", g, w)
+	}
+	if g, w := n, 0; g != w {
+		t.Errorf("Unexpectedly read %d bytes, wanted %d", g, w)
+	}
+}
+
+func TestTimeOutReader_nonEmptyReader(t *testing.T) {
+	msg := "Hello, World!"
+	buf := new(bytes.Buffer)
+	buf.WriteString(msg)
+	// empty read buffer
+	tor := TimeoutReader(buf)
+	var b []byte
+	n, err := tor.Read(b)
+	if err != nil || n != 0 {
+		t.Errorf("Empty buffer read returned n=%d err=%v", n, err)
+	}
+	// Second call should timeout
+	n, err = tor.Read(b)
+	if g, w := err, ErrTimeout; g != w {
+		t.Errorf("Error mismatch\n\tGot:  %v\n\tWant: %v", g, w)
+	}
+	if g, w := n, 0; g != w {
+		t.Errorf("Unexpectedly read %d bytes, wanted %d", g, w)
+	}
+	// non empty read buffer
+	tor2 := TimeoutReader(buf)
+	b = make([]byte, 3)
+	if n, err := tor2.Read(b); err != nil || n == 0 {
+		t.Errorf("Empty buffer read returned n=%d err=%v", n, err)
+	}
+	// Second call should timeout
+	n, err = tor2.Read(b)
+	if g, w := err, ErrTimeout; g != w {
+		t.Errorf("Error mismatch\n\tGot:  %v\n\tWant: %v", g, w)
+	}
+	if g, w := n, 0; g != w {
+		t.Errorf("Unexpectedly read %d bytes, wanted %d", g, w)
+	}
+}
+
+func TestTimeOutReader_emptyReader(t *testing.T) {
+	r := new(bytes.Buffer)
+	// empty read buffer
+	tor := TimeoutReader(r)
+	var b []byte
+	if n, err := tor.Read(b); err != nil || n != 0 {
+		t.Errorf("Empty buffer read returned n=%d err=%v", n, err)
+	}
+	// Second call should timeout
+	n, err := tor.Read(b)
+	if g, w := err, ErrTimeout; g != w {
+		t.Errorf("Error mismatch\n\tGot:  %v\n\tWant: %v", g, w)
+	}
+	if g, w := n, 0; g != w {
+		t.Errorf("Unexpectedly read %d bytes, wanted %d", g, w)
+	}
+	// non empty read buffer
+	tor2 := TimeoutReader(r)
+	b = make([]byte, 5)
+	if n, err := tor2.Read(b); err != io.EOF || n != 0 {
+		t.Errorf("Empty buffer read returned n=%d err=%v", n, err)
+	}
+	// Second call should timeout
+	n, err = tor2.Read(b)
+	if g, w := err, ErrTimeout; g != w {
+		t.Errorf("Error mismatch\n\tGot:  %v\n\tWant: %v", g, w)
+	}
+	if g, w := n, 0; g != w {
+		t.Errorf("Unexpectedly read %d bytes, wanted %d", g, w)
+	}
+}
+
+func TestDataErrReader_nonEmptyReader(t *testing.T) {
+	msg := "Hello, World!"
+	buf := new(bytes.Buffer)
+	buf.WriteString(msg)
+
+	der := DataErrReader(buf)
+
+	b := make([]byte, 3)
+	got := new(bytes.Buffer)
+	var n int
+	var err error
+	for {
+		n, err = der.Read(b)
+		got.Write(b[:n])
+		if err != nil {
+			break
+		}
+	}
+	if err != io.EOF || n == 0 {
+		t.Errorf("Last Read returned n=%d err=%v", n, err)
+	}
+	if g, w := got.String(), "Hello, World!"; g != w {
+		t.Errorf("Read mismatch\n\tGot:  %q\n\tWant: %q", g, w)
+	}
+}
+
+func TestDataErrReader_emptyReader(t *testing.T) {
+	r := new(bytes.Buffer)
+
+	der := DataErrReader(r)
+	var b []byte
+	if n, err := der.Read(b); err != io.EOF || n != 0 {
+		t.Errorf("Empty buffer read returned n=%d err=%v", n, err)
+	}
+
+	b = make([]byte, 5)
+	n, err := der.Read(b)
+	if g, w := err, io.EOF; g != w {
+		t.Errorf("Error mismatch\n\tGot:  %v\n\tWant: %v", g, w)
+	}
+	if g, w := n, 0; g != w {
+		t.Errorf("Unexpectedly read %d bytes, wanted %d", g, w)
+	}
+}
+
+func TestErrReader(t *testing.T) {
+	cases := []struct {
+		name string
+		err  error
+	}{
+		{"nil error", nil},
+		{"non-nil error", errors.New("io failure")},
+		{"io.EOF", io.EOF},
+	}
+
+	for _, tt := range cases {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			n, err := ErrReader(tt.err).Read(nil)
+			if err != tt.err {
+				t.Fatalf("Error mismatch\nGot:  %v\nWant: %v", err, tt.err)
+			}
+			if n != 0 {
+				t.Fatalf("Byte count mismatch: got %d want 0", n)
+			}
+		})
+	}
+}
+
+func TestStringsReader(t *testing.T) {
+	const msg = "Now is the time for all good gophers."
+
+	r := strings.NewReader(msg)
+	if err := TestReader(r, []byte(msg)); err != nil {
+		t.Fatal(err)
+	}
+}
diff --git a/src/testing/iotest/writer.go b/src/testing/iotest/writer.go
new file mode 100644
index 0000000..af61ab8
--- /dev/null
+++ b/src/testing/iotest/writer.go
@@ -0,0 +1,35 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package iotest
+
+import "io"
+
+// TruncateWriter returns a Writer that writes to w
+// but stops silently after n bytes.
+func TruncateWriter(w io.Writer, n int64) io.Writer {
+	return &truncateWriter{w, n}
+}
+
+type truncateWriter struct {
+	w io.Writer
+	n int64
+}
+
+func (t *truncateWriter) Write(p []byte) (n int, err error) {
+	if t.n <= 0 {
+		return len(p), nil
+	}
+	// real write
+	n = len(p)
+	if int64(n) > t.n {
+		n = int(t.n)
+	}
+	n, err = t.w.Write(p[0:n])
+	t.n -= int64(n)
+	if err == nil {
+		n = len(p)
+	}
+	return
+}
diff --git a/src/testing/iotest/writer_test.go b/src/testing/iotest/writer_test.go
new file mode 100644
index 0000000..5aaa77c
--- /dev/null
+++ b/src/testing/iotest/writer_test.go
@@ -0,0 +1,39 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package iotest
+
+import (
+	"bytes"
+	"testing"
+)
+
+var truncateWriterTests = []struct {
+	in    string
+	want  string
+	trunc int64
+	n     int
+}{
+	{"hello", "", -1, 5},
+	{"world", "", 0, 5},
+	{"abcde", "abc", 3, 5},
+	{"edcba", "edcba", 7, 5},
+}
+
+func TestTruncateWriter(t *testing.T) {
+	for _, tt := range truncateWriterTests {
+		buf := new(bytes.Buffer)
+		tw := TruncateWriter(buf, tt.trunc)
+		n, err := tw.Write([]byte(tt.in))
+		if err != nil {
+			t.Errorf("Unexpected error %v for\n\t%+v", err, tt)
+		}
+		if g, w := buf.String(), tt.want; g != w {
+			t.Errorf("got %q, expected %q", g, w)
+		}
+		if g, w := n, tt.n; g != w {
+			t.Errorf("read %d bytes, but expected to have read %d bytes for\n\t%+v", g, w, tt)
+		}
+	}
+}
diff --git a/src/testing/match.go b/src/testing/match.go
new file mode 100644
index 0000000..b18c6e7
--- /dev/null
+++ b/src/testing/match.go
@@ -0,0 +1,168 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testing
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"sync"
+)
+
+// matcher sanitizes, uniques, and filters names of subtests and subbenchmarks.
+type matcher struct {
+	filter    []string
+	matchFunc func(pat, str string) (bool, error)
+
+	mu       sync.Mutex
+	subNames map[string]int64
+}
+
+// TODO: fix test_main to avoid race and improve caching, also allowing to
+// eliminate this Mutex.
+var matchMutex sync.Mutex
+
+func newMatcher(matchString func(pat, str string) (bool, error), patterns, name string) *matcher {
+	var filter []string
+	if patterns != "" {
+		filter = splitRegexp(patterns)
+		for i, s := range filter {
+			filter[i] = rewrite(s)
+		}
+		// Verify filters before doing any processing.
+		for i, s := range filter {
+			if _, err := matchString(s, "non-empty"); err != nil {
+				fmt.Fprintf(os.Stderr, "testing: invalid regexp for element %d of %s (%q): %s\n", i, name, s, err)
+				os.Exit(1)
+			}
+		}
+	}
+	return &matcher{
+		filter:    filter,
+		matchFunc: matchString,
+		subNames:  map[string]int64{},
+	}
+}
+
+func (m *matcher) fullName(c *common, subname string) (name string, ok, partial bool) {
+	name = subname
+
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if c != nil && c.level > 0 {
+		name = m.unique(c.name, rewrite(subname))
+	}
+
+	matchMutex.Lock()
+	defer matchMutex.Unlock()
+
+	// We check the full array of paths each time to allow for the case that
+	// a pattern contains a '/'.
+	elem := strings.Split(name, "/")
+	for i, s := range elem {
+		if i >= len(m.filter) {
+			break
+		}
+		if ok, _ := m.matchFunc(m.filter[i], s); !ok {
+			return name, false, false
+		}
+	}
+	return name, true, len(elem) < len(m.filter)
+}
+
+func splitRegexp(s string) []string {
+	a := make([]string, 0, strings.Count(s, "/"))
+	cs := 0
+	cp := 0
+	for i := 0; i < len(s); {
+		switch s[i] {
+		case '[':
+			cs++
+		case ']':
+			if cs--; cs < 0 { // An unmatched ']' is legal.
+				cs = 0
+			}
+		case '(':
+			if cs == 0 {
+				cp++
+			}
+		case ')':
+			if cs == 0 {
+				cp--
+			}
+		case '\\':
+			i++
+		case '/':
+			if cs == 0 && cp == 0 {
+				a = append(a, s[:i])
+				s = s[i+1:]
+				i = 0
+				continue
+			}
+		}
+		i++
+	}
+	return append(a, s)
+}
+
+// unique creates a unique name for the given parent and subname by affixing it
+// with one or more counts, if necessary.
+func (m *matcher) unique(parent, subname string) string {
+	name := fmt.Sprintf("%s/%s", parent, subname)
+	empty := subname == ""
+	for {
+		next, exists := m.subNames[name]
+		if !empty && !exists {
+			m.subNames[name] = 1 // next count is 1
+			return name
+		}
+		// Name was already used. We increment with the count and append a
+		// string with the count.
+		m.subNames[name] = next + 1
+
+		// Add a count to guarantee uniqueness.
+		name = fmt.Sprintf("%s#%02d", name, next)
+		empty = false
+	}
+}
+
+// rewrite rewrites a subname to having only printable characters and no white
+// space.
+func rewrite(s string) string {
+	b := []byte{}
+	for _, r := range s {
+		switch {
+		case isSpace(r):
+			b = append(b, '_')
+		case !strconv.IsPrint(r):
+			s := strconv.QuoteRune(r)
+			b = append(b, s[1:len(s)-1]...)
+		default:
+			b = append(b, string(r)...)
+		}
+	}
+	return string(b)
+}
+
+func isSpace(r rune) bool {
+	if r < 0x2000 {
+		switch r {
+		// Note: not the same as Unicode Z class.
+		case '\t', '\n', '\v', '\f', '\r', ' ', 0x85, 0xA0, 0x1680:
+			return true
+		}
+	} else {
+		if r <= 0x200a {
+			return true
+		}
+		switch r {
+		case 0x2028, 0x2029, 0x202f, 0x205f, 0x3000:
+			return true
+		}
+	}
+	return false
+}
diff --git a/src/testing/match_test.go b/src/testing/match_test.go
new file mode 100644
index 0000000..8c09dc6
--- /dev/null
+++ b/src/testing/match_test.go
@@ -0,0 +1,186 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testing
+
+import (
+	"reflect"
+	"regexp"
+	"unicode"
+)
+
+// Verify that our IsSpace agrees with unicode.IsSpace.
+func TestIsSpace(t *T) {
+	n := 0
+	for r := rune(0); r <= unicode.MaxRune; r++ {
+		if isSpace(r) != unicode.IsSpace(r) {
+			t.Errorf("IsSpace(%U)=%t incorrect", r, isSpace(r))
+			n++
+			if n > 10 {
+				return
+			}
+		}
+	}
+}
+
+func TestSplitRegexp(t *T) {
+	res := func(s ...string) []string { return s }
+	testCases := []struct {
+		pattern string
+		result  []string
+	}{
+		// Correct patterns
+		// If a regexp pattern is correct, all split regexps need to be correct
+		// as well.
+		{"", res("")},
+		{"/", res("", "")},
+		{"//", res("", "", "")},
+		{"A", res("A")},
+		{"A/B", res("A", "B")},
+		{"A/B/", res("A", "B", "")},
+		{"/A/B/", res("", "A", "B", "")},
+		{"[A]/(B)", res("[A]", "(B)")},
+		{"[/]/[/]", res("[/]", "[/]")},
+		{"[/]/[:/]", res("[/]", "[:/]")},
+		{"/]", res("", "]")},
+		{"]/", res("]", "")},
+		{"]/[/]", res("]", "[/]")},
+		{`([)/][(])`, res(`([)/][(])`)},
+		{"[(]/[)]", res("[(]", "[)]")},
+
+		// Faulty patterns
+		// Errors in original should produce at least one faulty regexp in results.
+		{")/", res(")/")},
+		{")/(/)", res(")/(", ")")},
+		{"a[/)b", res("a[/)b")},
+		{"(/]", res("(/]")},
+		{"(/", res("(/")},
+		{"[/]/[/", res("[/]", "[/")},
+		{`\p{/}`, res(`\p{`, "}")},
+		{`\p/`, res(`\p`, "")},
+		{`[[:/:]]`, res(`[[:/:]]`)},
+	}
+	for _, tc := range testCases {
+		a := splitRegexp(tc.pattern)
+		if !reflect.DeepEqual(a, tc.result) {
+			t.Errorf("splitRegexp(%q) = %#v; want %#v", tc.pattern, a, tc.result)
+		}
+
+		// If there is any error in the pattern, one of the returned subpatterns
+		// needs to have an error as well.
+		if _, err := regexp.Compile(tc.pattern); err != nil {
+			ok := true
+			for _, re := range a {
+				if _, err := regexp.Compile(re); err != nil {
+					ok = false
+				}
+			}
+			if ok {
+				t.Errorf("%s: expected error in any of %q", tc.pattern, a)
+			}
+		}
+	}
+}
+
+func TestMatcher(t *T) {
+	testCases := []struct {
+		pattern     string
+		parent, sub string
+		ok          bool
+		partial     bool
+	}{
+		// Behavior without subtests.
+		{"", "", "TestFoo", true, false},
+		{"TestFoo", "", "TestFoo", true, false},
+		{"TestFoo/", "", "TestFoo", true, true},
+		{"TestFoo/bar/baz", "", "TestFoo", true, true},
+		{"TestFoo", "", "TestBar", false, false},
+		{"TestFoo/", "", "TestBar", false, false},
+		{"TestFoo/bar/baz", "", "TestBar/bar/baz", false, false},
+
+		// with subtests
+		{"", "TestFoo", "x", true, false},
+		{"TestFoo", "TestFoo", "x", true, false},
+		{"TestFoo/", "TestFoo", "x", true, false},
+		{"TestFoo/bar/baz", "TestFoo", "bar", true, true},
+		// Subtest with a '/' in its name still allows for copy and pasted names
+		// to match.
+		{"TestFoo/bar/baz", "TestFoo", "bar/baz", true, false},
+		{"TestFoo/bar/baz", "TestFoo/bar", "baz", true, false},
+		{"TestFoo/bar/baz", "TestFoo", "x", false, false},
+		{"TestFoo", "TestBar", "x", false, false},
+		{"TestFoo/", "TestBar", "x", false, false},
+		{"TestFoo/bar/baz", "TestBar", "x/bar/baz", false, false},
+
+		// subtests only
+		{"", "TestFoo", "x", true, false},
+		{"/", "TestFoo", "x", true, false},
+		{"./", "TestFoo", "x", true, false},
+		{"./.", "TestFoo", "x", true, false},
+		{"/bar/baz", "TestFoo", "bar", true, true},
+		{"/bar/baz", "TestFoo", "bar/baz", true, false},
+		{"//baz", "TestFoo", "bar/baz", true, false},
+		{"//", "TestFoo", "bar/baz", true, false},
+		{"/bar/baz", "TestFoo/bar", "baz", true, false},
+		{"//foo", "TestFoo", "bar/baz", false, false},
+		{"/bar/baz", "TestFoo", "x", false, false},
+		{"/bar/baz", "TestBar", "x/bar/baz", false, false},
+	}
+
+	for _, tc := range testCases {
+		m := newMatcher(regexp.MatchString, tc.pattern, "-test.run")
+
+		parent := &common{name: tc.parent}
+		if tc.parent != "" {
+			parent.level = 1
+		}
+		if n, ok, partial := m.fullName(parent, tc.sub); ok != tc.ok || partial != tc.partial {
+			t.Errorf("for pattern %q, fullName(parent=%q, sub=%q) = %q, ok %v partial %v; want ok %v partial %v",
+				tc.pattern, tc.parent, tc.sub, n, ok, partial, tc.ok, tc.partial)
+		}
+	}
+}
+
+func TestNaming(t *T) {
+	m := newMatcher(regexp.MatchString, "", "")
+
+	parent := &common{name: "x", level: 1} // top-level test.
+
+	// Rig the matcher with some preloaded values.
+	m.subNames["x/b"] = 1000
+
+	testCases := []struct {
+		name, want string
+	}{
+		// Uniqueness
+		{"", "x/#00"},
+		{"", "x/#01"},
+
+		{"t", "x/t"},
+		{"t", "x/t#01"},
+		{"t", "x/t#02"},
+
+		{"a#01", "x/a#01"}, // user has subtest with this name.
+		{"a", "x/a"},       // doesn't conflict with this name.
+		{"a", "x/a#01#01"}, // conflict, add disambiguating string.
+		{"a", "x/a#02"},    // This string is claimed now, so resume
+		{"a", "x/a#03"},    // with counting.
+		{"a#02", "x/a#02#01"},
+
+		{"b", "x/b#1000"}, // rigged, see above
+		{"b", "x/b#1001"},
+
+		// // Sanitizing
+		{"A:1 B:2", "x/A:1_B:2"},
+		{"s\t\r\u00a0", "x/s___"},
+		{"\x01", `x/\x01`},
+		{"\U0010ffff", `x/\U0010ffff`},
+	}
+
+	for i, tc := range testCases {
+		if got, _, _ := m.fullName(parent, tc.name); got != tc.want {
+			t.Errorf("%d:%s: got %q; want %q", i, tc.name, got, tc.want)
+		}
+	}
+}
diff --git a/src/testing/panic_test.go b/src/testing/panic_test.go
new file mode 100644
index 0000000..6b8b953
--- /dev/null
+++ b/src/testing/panic_test.go
@@ -0,0 +1,210 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testing_test
+
+import (
+	"flag"
+	"fmt"
+	"internal/testenv"
+	"os"
+	"os/exec"
+	"regexp"
+	"strings"
+	"testing"
+)
+
+var testPanicTest = flag.String("test_panic_test", "", "TestPanic: indicates which test should panic")
+var testPanicParallel = flag.Bool("test_panic_parallel", false, "TestPanic: run subtests in parallel")
+var testPanicCleanup = flag.Bool("test_panic_cleanup", false, "TestPanic: indicates whether test should call Cleanup")
+var testPanicCleanupPanic = flag.String("test_panic_cleanup_panic", "", "TestPanic: indicate whether test should call Cleanup function that panics")
+
+func TestPanic(t *testing.T) {
+	testenv.MustHaveExec(t)
+
+	testCases := []struct {
+		desc  string
+		flags []string
+		want  string
+	}{{
+		desc:  "root test panics",
+		flags: []string{"-test_panic_test=TestPanicHelper"},
+		want: `
+--- FAIL: TestPanicHelper (N.NNs)
+    panic_test.go:NNN: TestPanicHelper
+`,
+	}, {
+		desc:  "subtest panics",
+		flags: []string{"-test_panic_test=TestPanicHelper/1"},
+		want: `
+--- FAIL: TestPanicHelper (N.NNs)
+    panic_test.go:NNN: TestPanicHelper
+    --- FAIL: TestPanicHelper/1 (N.NNs)
+        panic_test.go:NNN: TestPanicHelper/1
+`,
+	}, {
+		desc:  "subtest panics with cleanup",
+		flags: []string{"-test_panic_test=TestPanicHelper/1", "-test_panic_cleanup"},
+		want: `
+ran inner cleanup 1
+ran middle cleanup 1
+ran outer cleanup
+--- FAIL: TestPanicHelper (N.NNs)
+    panic_test.go:NNN: TestPanicHelper
+    --- FAIL: TestPanicHelper/1 (N.NNs)
+        panic_test.go:NNN: TestPanicHelper/1
+`,
+	}, {
+		desc:  "subtest panics with outer cleanup panic",
+		flags: []string{"-test_panic_test=TestPanicHelper/1", "-test_panic_cleanup", "-test_panic_cleanup_panic=outer"},
+		want: `
+ran inner cleanup 1
+ran middle cleanup 1
+ran outer cleanup
+--- FAIL: TestPanicHelper (N.NNs)
+    panic_test.go:NNN: TestPanicHelper
+`,
+	}, {
+		desc:  "subtest panics with middle cleanup panic",
+		flags: []string{"-test_panic_test=TestPanicHelper/1", "-test_panic_cleanup", "-test_panic_cleanup_panic=middle"},
+		want: `
+ran inner cleanup 1
+ran middle cleanup 1
+ran outer cleanup
+--- FAIL: TestPanicHelper (N.NNs)
+    panic_test.go:NNN: TestPanicHelper
+    --- FAIL: TestPanicHelper/1 (N.NNs)
+        panic_test.go:NNN: TestPanicHelper/1
+`,
+	}, {
+		desc:  "subtest panics with inner cleanup panic",
+		flags: []string{"-test_panic_test=TestPanicHelper/1", "-test_panic_cleanup", "-test_panic_cleanup_panic=inner"},
+		want: `
+ran inner cleanup 1
+ran middle cleanup 1
+ran outer cleanup
+--- FAIL: TestPanicHelper (N.NNs)
+    panic_test.go:NNN: TestPanicHelper
+    --- FAIL: TestPanicHelper/1 (N.NNs)
+        panic_test.go:NNN: TestPanicHelper/1
+`,
+	}, {
+		desc:  "parallel subtest panics with cleanup",
+		flags: []string{"-test_panic_test=TestPanicHelper/1", "-test_panic_cleanup", "-test_panic_parallel"},
+		want: `
+ran inner cleanup 1
+ran middle cleanup 1
+ran outer cleanup
+--- FAIL: TestPanicHelper (N.NNs)
+    panic_test.go:NNN: TestPanicHelper
+    --- FAIL: TestPanicHelper/1 (N.NNs)
+        panic_test.go:NNN: TestPanicHelper/1
+`,
+	}, {
+		desc:  "parallel subtest panics with outer cleanup panic",
+		flags: []string{"-test_panic_test=TestPanicHelper/1", "-test_panic_cleanup", "-test_panic_cleanup_panic=outer", "-test_panic_parallel"},
+		want: `
+ran inner cleanup 1
+ran middle cleanup 1
+ran outer cleanup
+--- FAIL: TestPanicHelper (N.NNs)
+    panic_test.go:NNN: TestPanicHelper
+`,
+	}, {
+		desc:  "parallel subtest panics with middle cleanup panic",
+		flags: []string{"-test_panic_test=TestPanicHelper/1", "-test_panic_cleanup", "-test_panic_cleanup_panic=middle", "-test_panic_parallel"},
+		want: `
+ran inner cleanup 1
+ran middle cleanup 1
+ran outer cleanup
+--- FAIL: TestPanicHelper (N.NNs)
+    panic_test.go:NNN: TestPanicHelper
+    --- FAIL: TestPanicHelper/1 (N.NNs)
+        panic_test.go:NNN: TestPanicHelper/1
+`,
+	}, {
+		desc:  "parallel subtest panics with inner cleanup panic",
+		flags: []string{"-test_panic_test=TestPanicHelper/1", "-test_panic_cleanup", "-test_panic_cleanup_panic=inner", "-test_panic_parallel"},
+		want: `
+ran inner cleanup 1
+ran middle cleanup 1
+ran outer cleanup
+--- FAIL: TestPanicHelper (N.NNs)
+    panic_test.go:NNN: TestPanicHelper
+    --- FAIL: TestPanicHelper/1 (N.NNs)
+        panic_test.go:NNN: TestPanicHelper/1
+`,
+	}}
+	for _, tc := range testCases {
+		t.Run(tc.desc, func(t *testing.T) {
+			cmd := exec.Command(os.Args[0], "-test.run=TestPanicHelper")
+			cmd.Args = append(cmd.Args, tc.flags...)
+			cmd.Env = append(os.Environ(), "GO_WANT_HELPER_PROCESS=1")
+			b, _ := cmd.CombinedOutput()
+			got := string(b)
+			want := strings.TrimSpace(tc.want)
+			re := makeRegexp(want)
+			if ok, err := regexp.MatchString(re, got); !ok || err != nil {
+				t.Errorf("output:\ngot:\n%s\nwant:\n%s", got, want)
+			}
+		})
+	}
+}
+
+func makeRegexp(s string) string {
+	s = regexp.QuoteMeta(s)
+	s = strings.ReplaceAll(s, ":NNN:", `:\d+:`)
+	s = strings.ReplaceAll(s, "N\\.NNs", `\d*\.\d*s`)
+	return s
+}
+
+func TestPanicHelper(t *testing.T) {
+	if os.Getenv("GO_WANT_HELPER_PROCESS") != "1" {
+		return
+	}
+	t.Log(t.Name())
+	if t.Name() == *testPanicTest {
+		panic("panic")
+	}
+	switch *testPanicCleanupPanic {
+	case "", "outer", "middle", "inner":
+	default:
+		t.Fatalf("bad -test_panic_cleanup_panic: %s", *testPanicCleanupPanic)
+	}
+	t.Cleanup(func() {
+		fmt.Println("ran outer cleanup")
+		if *testPanicCleanupPanic == "outer" {
+			panic("outer cleanup")
+		}
+	})
+	for i := 0; i < 3; i++ {
+		i := i
+		t.Run(fmt.Sprintf("%v", i), func(t *testing.T) {
+			chosen := t.Name() == *testPanicTest
+			if chosen && *testPanicCleanup {
+				t.Cleanup(func() {
+					fmt.Printf("ran middle cleanup %d\n", i)
+					if *testPanicCleanupPanic == "middle" {
+						panic("middle cleanup")
+					}
+				})
+			}
+			if chosen && *testPanicParallel {
+				t.Parallel()
+			}
+			t.Log(t.Name())
+			if chosen {
+				if *testPanicCleanup {
+					t.Cleanup(func() {
+						fmt.Printf("ran inner cleanup %d\n", i)
+						if *testPanicCleanupPanic == "inner" {
+							panic("inner cleanup")
+						}
+					})
+				}
+				panic("panic")
+			}
+		})
+	}
+}
diff --git a/src/testing/quick/quick.go b/src/testing/quick/quick.go
new file mode 100644
index 0000000..c01647e
--- /dev/null
+++ b/src/testing/quick/quick.go
@@ -0,0 +1,385 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package quick implements utility functions to help with black box testing.
+//
+// The testing/quick package is frozen and is not accepting new features.
+package quick
+
+import (
+	"flag"
+	"fmt"
+	"math"
+	"math/rand"
+	"reflect"
+	"strings"
+	"time"
+)
+
+var defaultMaxCount *int = flag.Int("quickchecks", 100, "The default number of iterations for each check")
+
+// A Generator can generate random values of its own type.
+type Generator interface {
+	// Generate returns a random instance of the type on which it is a
+	// method using the size as a size hint.
+	Generate(rand *rand.Rand, size int) reflect.Value
+}
+
+// randFloat32 generates a random float taking the full range of a float32.
+func randFloat32(rand *rand.Rand) float32 {
+	f := rand.Float64() * math.MaxFloat32
+	if rand.Int()&1 == 1 {
+		f = -f
+	}
+	return float32(f)
+}
+
+// randFloat64 generates a random float taking the full range of a float64.
+func randFloat64(rand *rand.Rand) float64 {
+	f := rand.Float64() * math.MaxFloat64
+	if rand.Int()&1 == 1 {
+		f = -f
+	}
+	return f
+}
+
+// randInt64 returns a random int64.
+func randInt64(rand *rand.Rand) int64 {
+	return int64(rand.Uint64())
+}
+
+// complexSize is the maximum length of arbitrary values that contain other
+// values.
+const complexSize = 50
+
+// Value returns an arbitrary value of the given type.
+// If the type implements the Generator interface, that will be used.
+// Note: To create arbitrary values for structs, all the fields must be exported.
+func Value(t reflect.Type, rand *rand.Rand) (value reflect.Value, ok bool) {
+	return sizedValue(t, rand, complexSize)
+}
+
+// sizedValue returns an arbitrary value of the given type. The size
+// hint is used for shrinking as a function of indirection level so
+// that recursive data structures will terminate.
+func sizedValue(t reflect.Type, rand *rand.Rand, size int) (value reflect.Value, ok bool) {
+	if m, ok := reflect.Zero(t).Interface().(Generator); ok {
+		return m.Generate(rand, size), true
+	}
+
+	v := reflect.New(t).Elem()
+	switch concrete := t; concrete.Kind() {
+	case reflect.Bool:
+		v.SetBool(rand.Int()&1 == 0)
+	case reflect.Float32:
+		v.SetFloat(float64(randFloat32(rand)))
+	case reflect.Float64:
+		v.SetFloat(randFloat64(rand))
+	case reflect.Complex64:
+		v.SetComplex(complex(float64(randFloat32(rand)), float64(randFloat32(rand))))
+	case reflect.Complex128:
+		v.SetComplex(complex(randFloat64(rand), randFloat64(rand)))
+	case reflect.Int16:
+		v.SetInt(randInt64(rand))
+	case reflect.Int32:
+		v.SetInt(randInt64(rand))
+	case reflect.Int64:
+		v.SetInt(randInt64(rand))
+	case reflect.Int8:
+		v.SetInt(randInt64(rand))
+	case reflect.Int:
+		v.SetInt(randInt64(rand))
+	case reflect.Uint16:
+		v.SetUint(uint64(randInt64(rand)))
+	case reflect.Uint32:
+		v.SetUint(uint64(randInt64(rand)))
+	case reflect.Uint64:
+		v.SetUint(uint64(randInt64(rand)))
+	case reflect.Uint8:
+		v.SetUint(uint64(randInt64(rand)))
+	case reflect.Uint:
+		v.SetUint(uint64(randInt64(rand)))
+	case reflect.Uintptr:
+		v.SetUint(uint64(randInt64(rand)))
+	case reflect.Map:
+		numElems := rand.Intn(size)
+		v.Set(reflect.MakeMap(concrete))
+		for i := 0; i < numElems; i++ {
+			key, ok1 := sizedValue(concrete.Key(), rand, size)
+			value, ok2 := sizedValue(concrete.Elem(), rand, size)
+			if !ok1 || !ok2 {
+				return reflect.Value{}, false
+			}
+			v.SetMapIndex(key, value)
+		}
+	case reflect.Ptr:
+		if rand.Intn(size) == 0 {
+			v.Set(reflect.Zero(concrete)) // Generate nil pointer.
+		} else {
+			elem, ok := sizedValue(concrete.Elem(), rand, size)
+			if !ok {
+				return reflect.Value{}, false
+			}
+			v.Set(reflect.New(concrete.Elem()))
+			v.Elem().Set(elem)
+		}
+	case reflect.Slice:
+		numElems := rand.Intn(size)
+		sizeLeft := size - numElems
+		v.Set(reflect.MakeSlice(concrete, numElems, numElems))
+		for i := 0; i < numElems; i++ {
+			elem, ok := sizedValue(concrete.Elem(), rand, sizeLeft)
+			if !ok {
+				return reflect.Value{}, false
+			}
+			v.Index(i).Set(elem)
+		}
+	case reflect.Array:
+		for i := 0; i < v.Len(); i++ {
+			elem, ok := sizedValue(concrete.Elem(), rand, size)
+			if !ok {
+				return reflect.Value{}, false
+			}
+			v.Index(i).Set(elem)
+		}
+	case reflect.String:
+		numChars := rand.Intn(complexSize)
+		codePoints := make([]rune, numChars)
+		for i := 0; i < numChars; i++ {
+			codePoints[i] = rune(rand.Intn(0x10ffff))
+		}
+		v.SetString(string(codePoints))
+	case reflect.Struct:
+		n := v.NumField()
+		// Divide sizeLeft evenly among the struct fields.
+		sizeLeft := size
+		if n > sizeLeft {
+			sizeLeft = 1
+		} else if n > 0 {
+			sizeLeft /= n
+		}
+		for i := 0; i < n; i++ {
+			elem, ok := sizedValue(concrete.Field(i).Type, rand, sizeLeft)
+			if !ok {
+				return reflect.Value{}, false
+			}
+			v.Field(i).Set(elem)
+		}
+	default:
+		return reflect.Value{}, false
+	}
+
+	return v, true
+}
+
+// A Config structure contains options for running a test.
+type Config struct {
+	// MaxCount sets the maximum number of iterations.
+	// If zero, MaxCountScale is used.
+	MaxCount int
+	// MaxCountScale is a non-negative scale factor applied to the
+	// default maximum.
+	// A count of zero implies the default, which is usually 100
+	// but can be set by the -quickchecks flag.
+	MaxCountScale float64
+	// Rand specifies a source of random numbers.
+	// If nil, a default pseudo-random source will be used.
+	Rand *rand.Rand
+	// Values specifies a function to generate a slice of
+	// arbitrary reflect.Values that are congruent with the
+	// arguments to the function being tested.
+	// If nil, the top-level Value function is used to generate them.
+	Values func([]reflect.Value, *rand.Rand)
+}
+
+var defaultConfig Config
+
+// getRand returns the *rand.Rand to use for a given Config.
+func (c *Config) getRand() *rand.Rand {
+	if c.Rand == nil {
+		return rand.New(rand.NewSource(time.Now().UnixNano()))
+	}
+	return c.Rand
+}
+
+// getMaxCount returns the maximum number of iterations to run for a given
+// Config.
+func (c *Config) getMaxCount() (maxCount int) {
+	maxCount = c.MaxCount
+	if maxCount == 0 {
+		if c.MaxCountScale != 0 {
+			maxCount = int(c.MaxCountScale * float64(*defaultMaxCount))
+		} else {
+			maxCount = *defaultMaxCount
+		}
+	}
+
+	return
+}
+
+// A SetupError is the result of an error in the way that check is being
+// used, independent of the functions being tested.
+type SetupError string
+
+func (s SetupError) Error() string { return string(s) }
+
+// A CheckError is the result of Check finding an error.
+type CheckError struct {
+	Count int
+	In    []interface{}
+}
+
+func (s *CheckError) Error() string {
+	return fmt.Sprintf("#%d: failed on input %s", s.Count, toString(s.In))
+}
+
+// A CheckEqualError is the result CheckEqual finding an error.
+type CheckEqualError struct {
+	CheckError
+	Out1 []interface{}
+	Out2 []interface{}
+}
+
+func (s *CheckEqualError) Error() string {
+	return fmt.Sprintf("#%d: failed on input %s. Output 1: %s. Output 2: %s", s.Count, toString(s.In), toString(s.Out1), toString(s.Out2))
+}
+
+// Check looks for an input to f, any function that returns bool,
+// such that f returns false. It calls f repeatedly, with arbitrary
+// values for each argument. If f returns false on a given input,
+// Check returns that input as a *CheckError.
+// For example:
+//
+// 	func TestOddMultipleOfThree(t *testing.T) {
+// 		f := func(x int) bool {
+// 			y := OddMultipleOfThree(x)
+// 			return y%2 == 1 && y%3 == 0
+// 		}
+// 		if err := quick.Check(f, nil); err != nil {
+// 			t.Error(err)
+// 		}
+// 	}
+func Check(f interface{}, config *Config) error {
+	if config == nil {
+		config = &defaultConfig
+	}
+
+	fVal, fType, ok := functionAndType(f)
+	if !ok {
+		return SetupError("argument is not a function")
+	}
+
+	if fType.NumOut() != 1 {
+		return SetupError("function does not return one value")
+	}
+	if fType.Out(0).Kind() != reflect.Bool {
+		return SetupError("function does not return a bool")
+	}
+
+	arguments := make([]reflect.Value, fType.NumIn())
+	rand := config.getRand()
+	maxCount := config.getMaxCount()
+
+	for i := 0; i < maxCount; i++ {
+		err := arbitraryValues(arguments, fType, config, rand)
+		if err != nil {
+			return err
+		}
+
+		if !fVal.Call(arguments)[0].Bool() {
+			return &CheckError{i + 1, toInterfaces(arguments)}
+		}
+	}
+
+	return nil
+}
+
+// CheckEqual looks for an input on which f and g return different results.
+// It calls f and g repeatedly with arbitrary values for each argument.
+// If f and g return different answers, CheckEqual returns a *CheckEqualError
+// describing the input and the outputs.
+func CheckEqual(f, g interface{}, config *Config) error {
+	if config == nil {
+		config = &defaultConfig
+	}
+
+	x, xType, ok := functionAndType(f)
+	if !ok {
+		return SetupError("f is not a function")
+	}
+	y, yType, ok := functionAndType(g)
+	if !ok {
+		return SetupError("g is not a function")
+	}
+
+	if xType != yType {
+		return SetupError("functions have different types")
+	}
+
+	arguments := make([]reflect.Value, xType.NumIn())
+	rand := config.getRand()
+	maxCount := config.getMaxCount()
+
+	for i := 0; i < maxCount; i++ {
+		err := arbitraryValues(arguments, xType, config, rand)
+		if err != nil {
+			return err
+		}
+
+		xOut := toInterfaces(x.Call(arguments))
+		yOut := toInterfaces(y.Call(arguments))
+
+		if !reflect.DeepEqual(xOut, yOut) {
+			return &CheckEqualError{CheckError{i + 1, toInterfaces(arguments)}, xOut, yOut}
+		}
+	}
+
+	return nil
+}
+
+// arbitraryValues writes Values to args such that args contains Values
+// suitable for calling f.
+func arbitraryValues(args []reflect.Value, f reflect.Type, config *Config, rand *rand.Rand) (err error) {
+	if config.Values != nil {
+		config.Values(args, rand)
+		return
+	}
+
+	for j := 0; j < len(args); j++ {
+		var ok bool
+		args[j], ok = Value(f.In(j), rand)
+		if !ok {
+			err = SetupError(fmt.Sprintf("cannot create arbitrary value of type %s for argument %d", f.In(j), j))
+			return
+		}
+	}
+
+	return
+}
+
+func functionAndType(f interface{}) (v reflect.Value, t reflect.Type, ok bool) {
+	v = reflect.ValueOf(f)
+	ok = v.Kind() == reflect.Func
+	if !ok {
+		return
+	}
+	t = v.Type()
+	return
+}
+
+func toInterfaces(values []reflect.Value) []interface{} {
+	ret := make([]interface{}, len(values))
+	for i, v := range values {
+		ret[i] = v.Interface()
+	}
+	return ret
+}
+
+func toString(interfaces []interface{}) string {
+	s := make([]string, len(interfaces))
+	for i, v := range interfaces {
+		s[i] = fmt.Sprintf("%#v", v)
+	}
+	return strings.Join(s, ", ")
+}
diff --git a/src/testing/quick/quick_test.go b/src/testing/quick/quick_test.go
new file mode 100644
index 0000000..9df6dd4
--- /dev/null
+++ b/src/testing/quick/quick_test.go
@@ -0,0 +1,327 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package quick
+
+import (
+	"math/rand"
+	"reflect"
+	"testing"
+)
+
+func fArray(a [4]byte) [4]byte { return a }
+
+type TestArrayAlias [4]byte
+
+func fArrayAlias(a TestArrayAlias) TestArrayAlias { return a }
+
+func fBool(a bool) bool { return a }
+
+type TestBoolAlias bool
+
+func fBoolAlias(a TestBoolAlias) TestBoolAlias { return a }
+
+func fFloat32(a float32) float32 { return a }
+
+type TestFloat32Alias float32
+
+func fFloat32Alias(a TestFloat32Alias) TestFloat32Alias { return a }
+
+func fFloat64(a float64) float64 { return a }
+
+type TestFloat64Alias float64
+
+func fFloat64Alias(a TestFloat64Alias) TestFloat64Alias { return a }
+
+func fComplex64(a complex64) complex64 { return a }
+
+type TestComplex64Alias complex64
+
+func fComplex64Alias(a TestComplex64Alias) TestComplex64Alias { return a }
+
+func fComplex128(a complex128) complex128 { return a }
+
+type TestComplex128Alias complex128
+
+func fComplex128Alias(a TestComplex128Alias) TestComplex128Alias { return a }
+
+func fInt16(a int16) int16 { return a }
+
+type TestInt16Alias int16
+
+func fInt16Alias(a TestInt16Alias) TestInt16Alias { return a }
+
+func fInt32(a int32) int32 { return a }
+
+type TestInt32Alias int32
+
+func fInt32Alias(a TestInt32Alias) TestInt32Alias { return a }
+
+func fInt64(a int64) int64 { return a }
+
+type TestInt64Alias int64
+
+func fInt64Alias(a TestInt64Alias) TestInt64Alias { return a }
+
+func fInt8(a int8) int8 { return a }
+
+type TestInt8Alias int8
+
+func fInt8Alias(a TestInt8Alias) TestInt8Alias { return a }
+
+func fInt(a int) int { return a }
+
+type TestIntAlias int
+
+func fIntAlias(a TestIntAlias) TestIntAlias { return a }
+
+func fMap(a map[int]int) map[int]int { return a }
+
+type TestMapAlias map[int]int
+
+func fMapAlias(a TestMapAlias) TestMapAlias { return a }
+
+func fPtr(a *int) *int {
+	if a == nil {
+		return nil
+	}
+	b := *a
+	return &b
+}
+
+type TestPtrAlias *int
+
+func fPtrAlias(a TestPtrAlias) TestPtrAlias { return a }
+
+func fSlice(a []byte) []byte { return a }
+
+type TestSliceAlias []byte
+
+func fSliceAlias(a TestSliceAlias) TestSliceAlias { return a }
+
+func fString(a string) string { return a }
+
+type TestStringAlias string
+
+func fStringAlias(a TestStringAlias) TestStringAlias { return a }
+
+type TestStruct struct {
+	A int
+	B string
+}
+
+func fStruct(a TestStruct) TestStruct { return a }
+
+type TestStructAlias TestStruct
+
+func fStructAlias(a TestStructAlias) TestStructAlias { return a }
+
+func fUint16(a uint16) uint16 { return a }
+
+type TestUint16Alias uint16
+
+func fUint16Alias(a TestUint16Alias) TestUint16Alias { return a }
+
+func fUint32(a uint32) uint32 { return a }
+
+type TestUint32Alias uint32
+
+func fUint32Alias(a TestUint32Alias) TestUint32Alias { return a }
+
+func fUint64(a uint64) uint64 { return a }
+
+type TestUint64Alias uint64
+
+func fUint64Alias(a TestUint64Alias) TestUint64Alias { return a }
+
+func fUint8(a uint8) uint8 { return a }
+
+type TestUint8Alias uint8
+
+func fUint8Alias(a TestUint8Alias) TestUint8Alias { return a }
+
+func fUint(a uint) uint { return a }
+
+type TestUintAlias uint
+
+func fUintAlias(a TestUintAlias) TestUintAlias { return a }
+
+func fUintptr(a uintptr) uintptr { return a }
+
+type TestUintptrAlias uintptr
+
+func fUintptrAlias(a TestUintptrAlias) TestUintptrAlias { return a }
+
+func reportError(property string, err error, t *testing.T) {
+	if err != nil {
+		t.Errorf("%s: %s", property, err)
+	}
+}
+
+func TestCheckEqual(t *testing.T) {
+	reportError("fArray", CheckEqual(fArray, fArray, nil), t)
+	reportError("fArrayAlias", CheckEqual(fArrayAlias, fArrayAlias, nil), t)
+	reportError("fBool", CheckEqual(fBool, fBool, nil), t)
+	reportError("fBoolAlias", CheckEqual(fBoolAlias, fBoolAlias, nil), t)
+	reportError("fFloat32", CheckEqual(fFloat32, fFloat32, nil), t)
+	reportError("fFloat32Alias", CheckEqual(fFloat32Alias, fFloat32Alias, nil), t)
+	reportError("fFloat64", CheckEqual(fFloat64, fFloat64, nil), t)
+	reportError("fFloat64Alias", CheckEqual(fFloat64Alias, fFloat64Alias, nil), t)
+	reportError("fComplex64", CheckEqual(fComplex64, fComplex64, nil), t)
+	reportError("fComplex64Alias", CheckEqual(fComplex64Alias, fComplex64Alias, nil), t)
+	reportError("fComplex128", CheckEqual(fComplex128, fComplex128, nil), t)
+	reportError("fComplex128Alias", CheckEqual(fComplex128Alias, fComplex128Alias, nil), t)
+	reportError("fInt16", CheckEqual(fInt16, fInt16, nil), t)
+	reportError("fInt16Alias", CheckEqual(fInt16Alias, fInt16Alias, nil), t)
+	reportError("fInt32", CheckEqual(fInt32, fInt32, nil), t)
+	reportError("fInt32Alias", CheckEqual(fInt32Alias, fInt32Alias, nil), t)
+	reportError("fInt64", CheckEqual(fInt64, fInt64, nil), t)
+	reportError("fInt64Alias", CheckEqual(fInt64Alias, fInt64Alias, nil), t)
+	reportError("fInt8", CheckEqual(fInt8, fInt8, nil), t)
+	reportError("fInt8Alias", CheckEqual(fInt8Alias, fInt8Alias, nil), t)
+	reportError("fInt", CheckEqual(fInt, fInt, nil), t)
+	reportError("fIntAlias", CheckEqual(fIntAlias, fIntAlias, nil), t)
+	reportError("fInt32", CheckEqual(fInt32, fInt32, nil), t)
+	reportError("fInt32Alias", CheckEqual(fInt32Alias, fInt32Alias, nil), t)
+	reportError("fMap", CheckEqual(fMap, fMap, nil), t)
+	reportError("fMapAlias", CheckEqual(fMapAlias, fMapAlias, nil), t)
+	reportError("fPtr", CheckEqual(fPtr, fPtr, nil), t)
+	reportError("fPtrAlias", CheckEqual(fPtrAlias, fPtrAlias, nil), t)
+	reportError("fSlice", CheckEqual(fSlice, fSlice, nil), t)
+	reportError("fSliceAlias", CheckEqual(fSliceAlias, fSliceAlias, nil), t)
+	reportError("fString", CheckEqual(fString, fString, nil), t)
+	reportError("fStringAlias", CheckEqual(fStringAlias, fStringAlias, nil), t)
+	reportError("fStruct", CheckEqual(fStruct, fStruct, nil), t)
+	reportError("fStructAlias", CheckEqual(fStructAlias, fStructAlias, nil), t)
+	reportError("fUint16", CheckEqual(fUint16, fUint16, nil), t)
+	reportError("fUint16Alias", CheckEqual(fUint16Alias, fUint16Alias, nil), t)
+	reportError("fUint32", CheckEqual(fUint32, fUint32, nil), t)
+	reportError("fUint32Alias", CheckEqual(fUint32Alias, fUint32Alias, nil), t)
+	reportError("fUint64", CheckEqual(fUint64, fUint64, nil), t)
+	reportError("fUint64Alias", CheckEqual(fUint64Alias, fUint64Alias, nil), t)
+	reportError("fUint8", CheckEqual(fUint8, fUint8, nil), t)
+	reportError("fUint8Alias", CheckEqual(fUint8Alias, fUint8Alias, nil), t)
+	reportError("fUint", CheckEqual(fUint, fUint, nil), t)
+	reportError("fUintAlias", CheckEqual(fUintAlias, fUintAlias, nil), t)
+	reportError("fUintptr", CheckEqual(fUintptr, fUintptr, nil), t)
+	reportError("fUintptrAlias", CheckEqual(fUintptrAlias, fUintptrAlias, nil), t)
+}
+
+// This tests that ArbitraryValue is working by checking that all the arbitrary
+// values of type MyStruct have x = 42.
+type myStruct struct {
+	x int
+}
+
+func (m myStruct) Generate(r *rand.Rand, _ int) reflect.Value {
+	return reflect.ValueOf(myStruct{x: 42})
+}
+
+func myStructProperty(in myStruct) bool { return in.x == 42 }
+
+func TestCheckProperty(t *testing.T) {
+	reportError("myStructProperty", Check(myStructProperty, nil), t)
+}
+
+func TestFailure(t *testing.T) {
+	f := func(x int) bool { return false }
+	err := Check(f, nil)
+	if err == nil {
+		t.Errorf("Check didn't return an error")
+	}
+	if _, ok := err.(*CheckError); !ok {
+		t.Errorf("Error was not a CheckError: %s", err)
+	}
+
+	err = CheckEqual(fUint, fUint32, nil)
+	if err == nil {
+		t.Errorf("#1 CheckEqual didn't return an error")
+	}
+	if _, ok := err.(SetupError); !ok {
+		t.Errorf("#1 Error was not a SetupError: %s", err)
+	}
+
+	err = CheckEqual(func(x, y int) {}, func(x int) {}, nil)
+	if err == nil {
+		t.Errorf("#2 CheckEqual didn't return an error")
+	}
+	if _, ok := err.(SetupError); !ok {
+		t.Errorf("#2 Error was not a SetupError: %s", err)
+	}
+
+	err = CheckEqual(func(x int) int { return 0 }, func(x int) int32 { return 0 }, nil)
+	if err == nil {
+		t.Errorf("#3 CheckEqual didn't return an error")
+	}
+	if _, ok := err.(SetupError); !ok {
+		t.Errorf("#3 Error was not a SetupError: %s", err)
+	}
+}
+
+// Recursive data structures didn't terminate.
+// Issues 8818 and 11148.
+func TestRecursive(t *testing.T) {
+	type R struct {
+		Ptr      *R
+		SliceP   []*R
+		Slice    []R
+		Map      map[int]R
+		MapP     map[int]*R
+		MapR     map[*R]*R
+		SliceMap []map[int]R
+	}
+
+	f := func(r R) bool { return true }
+	Check(f, nil)
+}
+
+func TestEmptyStruct(t *testing.T) {
+	f := func(struct{}) bool { return true }
+	Check(f, nil)
+}
+
+type (
+	A struct{ B *B }
+	B struct{ A *A }
+)
+
+func TestMutuallyRecursive(t *testing.T) {
+	f := func(a A) bool { return true }
+	Check(f, nil)
+}
+
+// Some serialization formats (e.g. encoding/pem) cannot distinguish
+// between a nil and an empty map or slice, so avoid generating the
+// zero value for these.
+func TestNonZeroSliceAndMap(t *testing.T) {
+	type Q struct {
+		M map[int]int
+		S []int
+	}
+	f := func(q Q) bool {
+		return q.M != nil && q.S != nil
+	}
+	err := Check(f, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestInt64(t *testing.T) {
+	var lo, hi int64
+	f := func(x int64) bool {
+		if x < lo {
+			lo = x
+		}
+		if x > hi {
+			hi = x
+		}
+		return true
+	}
+	cfg := &Config{MaxCount: 10000}
+	Check(f, cfg)
+	if uint64(lo)>>62 == 0 || uint64(hi)>>62 == 0 {
+		t.Errorf("int64 returned range %#016x,%#016x; does not look like full range", lo, hi)
+	}
+}
diff --git a/src/testing/run_example.go b/src/testing/run_example.go
new file mode 100644
index 0000000..4dc83f7
--- /dev/null
+++ b/src/testing/run_example.go
@@ -0,0 +1,66 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !js
+
+// TODO(@musiol, @odeke-em): re-unify this entire file back into
+// example.go when js/wasm gets an os.Pipe implementation
+// and no longer needs this separation.
+
+package testing
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"time"
+)
+
+func runExample(eg InternalExample) (ok bool) {
+	if *chatty {
+		fmt.Printf("=== RUN   %s\n", eg.Name)
+	}
+
+	// Capture stdout.
+	stdout := os.Stdout
+	r, w, err := os.Pipe()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	os.Stdout = w
+	outC := make(chan string)
+	go func() {
+		var buf strings.Builder
+		_, err := io.Copy(&buf, r)
+		r.Close()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "testing: copying pipe: %v\n", err)
+			os.Exit(1)
+		}
+		outC <- buf.String()
+	}()
+
+	finished := false
+	start := time.Now()
+
+	// Clean up in a deferred call so we can recover if the example panics.
+	defer func() {
+		timeSpent := time.Since(start)
+
+		// Close pipe, restore stdout, get output.
+		w.Close()
+		os.Stdout = stdout
+		out := <-outC
+
+		err := recover()
+		ok = eg.processRunResult(out, timeSpent, finished, err)
+	}()
+
+	// Run example.
+	eg.F()
+	finished = true
+	return
+}
diff --git a/src/testing/run_example_js.go b/src/testing/run_example_js.go
new file mode 100644
index 0000000..1d4164b
--- /dev/null
+++ b/src/testing/run_example_js.go
@@ -0,0 +1,76 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build js
+
+package testing
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"time"
+)
+
+// TODO(@musiol, @odeke-em): unify this code back into
+// example.go when js/wasm gets an os.Pipe implementation.
+func runExample(eg InternalExample) (ok bool) {
+	if *chatty {
+		fmt.Printf("=== RUN   %s\n", eg.Name)
+	}
+
+	// Capture stdout to temporary file. We're not using
+	// os.Pipe because it is not supported on js/wasm.
+	stdout := os.Stdout
+	f := createTempFile(eg.Name)
+	os.Stdout = f
+	finished := false
+	start := time.Now()
+
+	// Clean up in a deferred call so we can recover if the example panics.
+	defer func() {
+		timeSpent := time.Since(start)
+
+		// Restore stdout, get output and remove temporary file.
+		os.Stdout = stdout
+		var buf strings.Builder
+		_, seekErr := f.Seek(0, os.SEEK_SET)
+		_, readErr := io.Copy(&buf, f)
+		out := buf.String()
+		f.Close()
+		os.Remove(f.Name())
+		if seekErr != nil {
+			fmt.Fprintf(os.Stderr, "testing: seek temp file: %v\n", seekErr)
+			os.Exit(1)
+		}
+		if readErr != nil {
+			fmt.Fprintf(os.Stderr, "testing: read temp file: %v\n", readErr)
+			os.Exit(1)
+		}
+
+		err := recover()
+		ok = eg.processRunResult(out, timeSpent, finished, err)
+	}()
+
+	// Run example.
+	eg.F()
+	finished = true
+	return
+}
+
+func createTempFile(exampleName string) *os.File {
+	for i := 0; ; i++ {
+		name := fmt.Sprintf("%s/go-example-stdout-%s-%d.txt", os.TempDir(), exampleName, i)
+		f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
+		if err != nil {
+			if os.IsExist(err) {
+				continue
+			}
+			fmt.Fprintf(os.Stderr, "testing: open temp file: %v\n", err)
+			os.Exit(1)
+		}
+		return f
+	}
+}
diff --git a/src/testing/sub_test.go b/src/testing/sub_test.go
new file mode 100644
index 0000000..5b226f8
--- /dev/null
+++ b/src/testing/sub_test.go
@@ -0,0 +1,966 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testing
+
+import (
+	"bytes"
+	"fmt"
+	"reflect"
+	"regexp"
+	"runtime"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+func init() {
+	// Make benchmark tests run 10x faster.
+	benchTime.d = 100 * time.Millisecond
+}
+
+func TestTestContext(t *T) {
+	const (
+		add1 = 0
+		done = 1
+	)
+	// After each of the calls are applied to the context, the
+	type call struct {
+		typ int // run or done
+		// result from applying the call
+		running int
+		waiting int
+		started bool
+	}
+	testCases := []struct {
+		max int
+		run []call
+	}{{
+		max: 1,
+		run: []call{
+			{typ: add1, running: 1, waiting: 0, started: true},
+			{typ: done, running: 0, waiting: 0, started: false},
+		},
+	}, {
+		max: 1,
+		run: []call{
+			{typ: add1, running: 1, waiting: 0, started: true},
+			{typ: add1, running: 1, waiting: 1, started: false},
+			{typ: done, running: 1, waiting: 0, started: true},
+			{typ: done, running: 0, waiting: 0, started: false},
+			{typ: add1, running: 1, waiting: 0, started: true},
+		},
+	}, {
+		max: 3,
+		run: []call{
+			{typ: add1, running: 1, waiting: 0, started: true},
+			{typ: add1, running: 2, waiting: 0, started: true},
+			{typ: add1, running: 3, waiting: 0, started: true},
+			{typ: add1, running: 3, waiting: 1, started: false},
+			{typ: add1, running: 3, waiting: 2, started: false},
+			{typ: add1, running: 3, waiting: 3, started: false},
+			{typ: done, running: 3, waiting: 2, started: true},
+			{typ: add1, running: 3, waiting: 3, started: false},
+			{typ: done, running: 3, waiting: 2, started: true},
+			{typ: done, running: 3, waiting: 1, started: true},
+			{typ: done, running: 3, waiting: 0, started: true},
+			{typ: done, running: 2, waiting: 0, started: false},
+			{typ: done, running: 1, waiting: 0, started: false},
+			{typ: done, running: 0, waiting: 0, started: false},
+		},
+	}}
+	for i, tc := range testCases {
+		ctx := &testContext{
+			startParallel: make(chan bool),
+			maxParallel:   tc.max,
+		}
+		for j, call := range tc.run {
+			doCall := func(f func()) chan bool {
+				done := make(chan bool)
+				go func() {
+					f()
+					done <- true
+				}()
+				return done
+			}
+			started := false
+			switch call.typ {
+			case add1:
+				signal := doCall(ctx.waitParallel)
+				select {
+				case <-signal:
+					started = true
+				case ctx.startParallel <- true:
+					<-signal
+				}
+			case done:
+				signal := doCall(ctx.release)
+				select {
+				case <-signal:
+				case <-ctx.startParallel:
+					started = true
+					<-signal
+				}
+			}
+			if started != call.started {
+				t.Errorf("%d:%d:started: got %v; want %v", i, j, started, call.started)
+			}
+			if ctx.running != call.running {
+				t.Errorf("%d:%d:running: got %v; want %v", i, j, ctx.running, call.running)
+			}
+			if ctx.numWaiting != call.waiting {
+				t.Errorf("%d:%d:waiting: got %v; want %v", i, j, ctx.numWaiting, call.waiting)
+			}
+		}
+	}
+}
+
+func TestTRun(t *T) {
+	realTest := t
+	testCases := []struct {
+		desc   string
+		ok     bool
+		maxPar int
+		chatty bool
+		output string
+		f      func(*T)
+	}{{
+		desc:   "failnow skips future sequential and parallel tests at same level",
+		ok:     false,
+		maxPar: 1,
+		output: `
+--- FAIL: failnow skips future sequential and parallel tests at same level (N.NNs)
+    --- FAIL: failnow skips future sequential and parallel tests at same level/#00 (N.NNs)
+    `,
+		f: func(t *T) {
+			ranSeq := false
+			ranPar := false
+			t.Run("", func(t *T) {
+				t.Run("par", func(t *T) {
+					t.Parallel()
+					ranPar = true
+				})
+				t.Run("seq", func(t *T) {
+					ranSeq = true
+				})
+				t.FailNow()
+				t.Run("seq", func(t *T) {
+					realTest.Error("test must be skipped")
+				})
+				t.Run("par", func(t *T) {
+					t.Parallel()
+					realTest.Error("test must be skipped.")
+				})
+			})
+			if !ranPar {
+				realTest.Error("parallel test was not run")
+			}
+			if !ranSeq {
+				realTest.Error("sequential test was not run")
+			}
+		},
+	}, {
+		desc:   "failure in parallel test propagates upwards",
+		ok:     false,
+		maxPar: 1,
+		output: `
+--- FAIL: failure in parallel test propagates upwards (N.NNs)
+    --- FAIL: failure in parallel test propagates upwards/#00 (N.NNs)
+        --- FAIL: failure in parallel test propagates upwards/#00/par (N.NNs)
+        `,
+		f: func(t *T) {
+			t.Run("", func(t *T) {
+				t.Parallel()
+				t.Run("par", func(t *T) {
+					t.Parallel()
+					t.Fail()
+				})
+			})
+		},
+	}, {
+		desc:   "skipping without message, chatty",
+		ok:     true,
+		chatty: true,
+		output: `
+=== RUN   skipping without message, chatty
+--- SKIP: skipping without message, chatty (N.NNs)`,
+		f: func(t *T) { t.SkipNow() },
+	}, {
+		desc:   "chatty with recursion",
+		ok:     true,
+		chatty: true,
+		output: `
+=== RUN   chatty with recursion
+=== RUN   chatty with recursion/#00
+=== RUN   chatty with recursion/#00/#00
+--- PASS: chatty with recursion (N.NNs)
+    --- PASS: chatty with recursion/#00 (N.NNs)
+        --- PASS: chatty with recursion/#00/#00 (N.NNs)`,
+		f: func(t *T) {
+			t.Run("", func(t *T) {
+				t.Run("", func(t *T) {})
+			})
+		},
+	}, {
+		desc: "skipping without message, not chatty",
+		ok:   true,
+		f:    func(t *T) { t.SkipNow() },
+	}, {
+		desc: "skipping after error",
+		output: `
+--- FAIL: skipping after error (N.NNs)
+    sub_test.go:NNN: an error
+    sub_test.go:NNN: skipped`,
+		f: func(t *T) {
+			t.Error("an error")
+			t.Skip("skipped")
+		},
+	}, {
+		desc:   "use Run to locally synchronize parallelism",
+		ok:     true,
+		maxPar: 1,
+		f: func(t *T) {
+			var count uint32
+			t.Run("waitGroup", func(t *T) {
+				for i := 0; i < 4; i++ {
+					t.Run("par", func(t *T) {
+						t.Parallel()
+						atomic.AddUint32(&count, 1)
+					})
+				}
+			})
+			if count != 4 {
+				t.Errorf("count was %d; want 4", count)
+			}
+		},
+	}, {
+		desc: "alternate sequential and parallel",
+		// Sequential tests should partake in the counting of running threads.
+		// Otherwise, if one runs parallel subtests in sequential tests that are
+		// itself subtests of parallel tests, the counts can get askew.
+		ok:     true,
+		maxPar: 1,
+		f: func(t *T) {
+			t.Run("a", func(t *T) {
+				t.Parallel()
+				t.Run("b", func(t *T) {
+					// Sequential: ensure running count is decremented.
+					t.Run("c", func(t *T) {
+						t.Parallel()
+					})
+
+				})
+			})
+		},
+	}, {
+		desc: "alternate sequential and parallel 2",
+		// Sequential tests should partake in the counting of running threads.
+		// Otherwise, if one runs parallel subtests in sequential tests that are
+		// itself subtests of parallel tests, the counts can get askew.
+		ok:     true,
+		maxPar: 2,
+		f: func(t *T) {
+			for i := 0; i < 2; i++ {
+				t.Run("a", func(t *T) {
+					t.Parallel()
+					time.Sleep(time.Nanosecond)
+					for i := 0; i < 2; i++ {
+						t.Run("b", func(t *T) {
+							time.Sleep(time.Nanosecond)
+							for i := 0; i < 2; i++ {
+								t.Run("c", func(t *T) {
+									t.Parallel()
+									time.Sleep(time.Nanosecond)
+								})
+							}
+
+						})
+					}
+				})
+			}
+		},
+	}, {
+		desc:   "stress test",
+		ok:     true,
+		maxPar: 4,
+		f: func(t *T) {
+			t.Parallel()
+			for i := 0; i < 12; i++ {
+				t.Run("a", func(t *T) {
+					t.Parallel()
+					time.Sleep(time.Nanosecond)
+					for i := 0; i < 12; i++ {
+						t.Run("b", func(t *T) {
+							time.Sleep(time.Nanosecond)
+							for i := 0; i < 12; i++ {
+								t.Run("c", func(t *T) {
+									t.Parallel()
+									time.Sleep(time.Nanosecond)
+									t.Run("d1", func(t *T) {})
+									t.Run("d2", func(t *T) {})
+									t.Run("d3", func(t *T) {})
+									t.Run("d4", func(t *T) {})
+								})
+							}
+						})
+					}
+				})
+			}
+		},
+	}, {
+		desc:   "skip output",
+		ok:     true,
+		maxPar: 4,
+		f: func(t *T) {
+			t.Skip()
+		},
+	}, {
+		desc: "subtest calls error on parent",
+		ok:   false,
+		output: `
+--- FAIL: subtest calls error on parent (N.NNs)
+    sub_test.go:NNN: first this
+    sub_test.go:NNN: and now this!
+    sub_test.go:NNN: oh, and this too`,
+		maxPar: 1,
+		f: func(t *T) {
+			t.Errorf("first this")
+			outer := t
+			t.Run("", func(t *T) {
+				outer.Errorf("and now this!")
+			})
+			t.Errorf("oh, and this too")
+		},
+	}, {
+		desc: "subtest calls fatal on parent",
+		ok:   false,
+		output: `
+--- FAIL: subtest calls fatal on parent (N.NNs)
+    sub_test.go:NNN: first this
+    sub_test.go:NNN: and now this!
+    --- FAIL: subtest calls fatal on parent/#00 (N.NNs)
+        testing.go:NNN: test executed panic(nil) or runtime.Goexit: subtest may have called FailNow on a parent test`,
+		maxPar: 1,
+		f: func(t *T) {
+			outer := t
+			t.Errorf("first this")
+			t.Run("", func(t *T) {
+				outer.Fatalf("and now this!")
+			})
+			t.Errorf("Should not reach here.")
+		},
+	}, {
+		desc: "subtest calls error on ancestor",
+		ok:   false,
+		output: `
+--- FAIL: subtest calls error on ancestor (N.NNs)
+    sub_test.go:NNN: Report to ancestor
+    --- FAIL: subtest calls error on ancestor/#00 (N.NNs)
+        sub_test.go:NNN: Still do this
+    sub_test.go:NNN: Also do this`,
+		maxPar: 1,
+		f: func(t *T) {
+			outer := t
+			t.Run("", func(t *T) {
+				t.Run("", func(t *T) {
+					outer.Errorf("Report to ancestor")
+				})
+				t.Errorf("Still do this")
+			})
+			t.Errorf("Also do this")
+		},
+	}, {
+		desc: "subtest calls fatal on ancestor",
+		ok:   false,
+		output: `
+--- FAIL: subtest calls fatal on ancestor (N.NNs)
+    sub_test.go:NNN: Nope`,
+		maxPar: 1,
+		f: func(t *T) {
+			outer := t
+			t.Run("", func(t *T) {
+				for i := 0; i < 4; i++ {
+					t.Run("", func(t *T) {
+						outer.Fatalf("Nope")
+					})
+					t.Errorf("Don't do this")
+				}
+				t.Errorf("And neither do this")
+			})
+			t.Errorf("Nor this")
+		},
+	}, {
+		desc:   "panic on goroutine fail after test exit",
+		ok:     false,
+		maxPar: 4,
+		f: func(t *T) {
+			ch := make(chan bool)
+			t.Run("", func(t *T) {
+				go func() {
+					<-ch
+					defer func() {
+						if r := recover(); r == nil {
+							realTest.Errorf("expected panic")
+						}
+						ch <- true
+					}()
+					t.Errorf("failed after success")
+				}()
+			})
+			ch <- true
+			<-ch
+		},
+	}, {
+		desc: "log in finished sub test logs to parent",
+		ok:   false,
+		output: `
+		--- FAIL: log in finished sub test logs to parent (N.NNs)
+    sub_test.go:NNN: message2
+    sub_test.go:NNN: message1
+    sub_test.go:NNN: error`,
+		maxPar: 1,
+		f: func(t *T) {
+			ch := make(chan bool)
+			t.Run("sub", func(t2 *T) {
+				go func() {
+					<-ch
+					t2.Log("message1")
+					ch <- true
+				}()
+			})
+			t.Log("message2")
+			ch <- true
+			<-ch
+			t.Errorf("error")
+		},
+	}, {
+		// A chatty test should always log with fmt.Print, even if the
+		// parent test has completed.
+		desc:   "log in finished sub test with chatty",
+		ok:     false,
+		chatty: true,
+		output: `
+		--- FAIL: log in finished sub test with chatty (N.NNs)`,
+		maxPar: 1,
+		f: func(t *T) {
+			ch := make(chan bool)
+			t.Run("sub", func(t2 *T) {
+				go func() {
+					<-ch
+					t2.Log("message1")
+					ch <- true
+				}()
+			})
+			t.Log("message2")
+			ch <- true
+			<-ch
+			t.Errorf("error")
+		},
+	}, {
+		// If a subtest panics we should run cleanups.
+		desc:   "cleanup when subtest panics",
+		ok:     false,
+		chatty: false,
+		output: `
+--- FAIL: cleanup when subtest panics (N.NNs)
+    --- FAIL: cleanup when subtest panics/sub (N.NNs)
+    sub_test.go:NNN: running cleanup`,
+		f: func(t *T) {
+			t.Cleanup(func() { t.Log("running cleanup") })
+			t.Run("sub", func(t2 *T) {
+				t2.FailNow()
+			})
+		},
+	}}
+	for _, tc := range testCases {
+		t.Run(tc.desc, func(t *T) {
+			ctx := newTestContext(tc.maxPar, newMatcher(regexp.MatchString, "", ""))
+			buf := &bytes.Buffer{}
+			root := &T{
+				common: common{
+					signal: make(chan bool),
+					name:   "Test",
+					w:      buf,
+				},
+				context: ctx,
+			}
+			if tc.chatty {
+				root.chatty = newChattyPrinter(root.w)
+			}
+			ok := root.Run(tc.desc, tc.f)
+			ctx.release()
+
+			if ok != tc.ok {
+				t.Errorf("%s:ok: got %v; want %v", tc.desc, ok, tc.ok)
+			}
+			if ok != !root.Failed() {
+				t.Errorf("%s:root failed: got %v; want %v", tc.desc, !ok, root.Failed())
+			}
+			if ctx.running != 0 || ctx.numWaiting != 0 {
+				t.Errorf("%s:running and waiting non-zero: got %d and %d", tc.desc, ctx.running, ctx.numWaiting)
+			}
+			got := strings.TrimSpace(buf.String())
+			want := strings.TrimSpace(tc.output)
+			re := makeRegexp(want)
+			if ok, err := regexp.MatchString(re, got); !ok || err != nil {
+				t.Errorf("%s:output:\ngot:\n%s\nwant:\n%s", tc.desc, got, want)
+			}
+		})
+	}
+}
+
+func TestBRun(t *T) {
+	work := func(b *B) {
+		for i := 0; i < b.N; i++ {
+			time.Sleep(time.Nanosecond)
+		}
+	}
+	testCases := []struct {
+		desc   string
+		failed bool
+		chatty bool
+		output string
+		f      func(*B)
+	}{{
+		desc: "simulate sequential run of subbenchmarks.",
+		f: func(b *B) {
+			b.Run("", func(b *B) { work(b) })
+			time1 := b.result.NsPerOp()
+			b.Run("", func(b *B) { work(b) })
+			time2 := b.result.NsPerOp()
+			if time1 >= time2 {
+				t.Errorf("no time spent in benchmark t1 >= t2 (%d >= %d)", time1, time2)
+			}
+		},
+	}, {
+		desc: "bytes set by all benchmarks",
+		f: func(b *B) {
+			b.Run("", func(b *B) { b.SetBytes(10); work(b) })
+			b.Run("", func(b *B) { b.SetBytes(10); work(b) })
+			if b.result.Bytes != 20 {
+				t.Errorf("bytes: got: %d; want 20", b.result.Bytes)
+			}
+		},
+	}, {
+		desc: "bytes set by some benchmarks",
+		// In this case the bytes result is meaningless, so it must be 0.
+		f: func(b *B) {
+			b.Run("", func(b *B) { b.SetBytes(10); work(b) })
+			b.Run("", func(b *B) { work(b) })
+			b.Run("", func(b *B) { b.SetBytes(10); work(b) })
+			if b.result.Bytes != 0 {
+				t.Errorf("bytes: got: %d; want 0", b.result.Bytes)
+			}
+		},
+	}, {
+		desc:   "failure carried over to root",
+		failed: true,
+		output: "--- FAIL: root",
+		f:      func(b *B) { b.Fail() },
+	}, {
+		desc:   "skipping without message, chatty",
+		chatty: true,
+		output: "--- SKIP: root",
+		f:      func(b *B) { b.SkipNow() },
+	}, {
+		desc:   "chatty with recursion",
+		chatty: true,
+		f: func(b *B) {
+			b.Run("", func(b *B) {
+				b.Run("", func(b *B) {})
+			})
+		},
+	}, {
+		desc: "skipping without message, not chatty",
+		f:    func(b *B) { b.SkipNow() },
+	}, {
+		desc:   "skipping after error",
+		failed: true,
+		output: `
+--- FAIL: root
+    sub_test.go:NNN: an error
+    sub_test.go:NNN: skipped`,
+		f: func(b *B) {
+			b.Error("an error")
+			b.Skip("skipped")
+		},
+	}, {
+		desc: "memory allocation",
+		f: func(b *B) {
+			const bufSize = 256
+			alloc := func(b *B) {
+				var buf [bufSize]byte
+				for i := 0; i < b.N; i++ {
+					_ = append([]byte(nil), buf[:]...)
+				}
+			}
+			b.Run("", func(b *B) {
+				alloc(b)
+				b.ReportAllocs()
+			})
+			b.Run("", func(b *B) {
+				alloc(b)
+				b.ReportAllocs()
+			})
+			// runtime.MemStats sometimes reports more allocations than the
+			// benchmark is responsible for. Luckily the point of this test is
+			// to ensure that the results are not underreported, so we can
+			// simply verify the lower bound.
+			if got := b.result.MemAllocs; got < 2 {
+				t.Errorf("MemAllocs was %v; want 2", got)
+			}
+			if got := b.result.MemBytes; got < 2*bufSize {
+				t.Errorf("MemBytes was %v; want %v", got, 2*bufSize)
+			}
+		},
+	}, {
+		desc: "cleanup is called",
+		f: func(b *B) {
+			var calls, cleanups, innerCalls, innerCleanups int
+			b.Run("", func(b *B) {
+				calls++
+				b.Cleanup(func() {
+					cleanups++
+				})
+				b.Run("", func(b *B) {
+					b.Cleanup(func() {
+						innerCleanups++
+					})
+					innerCalls++
+				})
+				work(b)
+			})
+			if calls == 0 || calls != cleanups {
+				t.Errorf("mismatched cleanups; got %d want %d", cleanups, calls)
+			}
+			if innerCalls == 0 || innerCalls != innerCleanups {
+				t.Errorf("mismatched cleanups; got %d want %d", cleanups, calls)
+			}
+		},
+	}, {
+		desc:   "cleanup is called on failure",
+		failed: true,
+		f: func(b *B) {
+			var calls, cleanups int
+			b.Run("", func(b *B) {
+				calls++
+				b.Cleanup(func() {
+					cleanups++
+				})
+				b.Fatalf("failure")
+			})
+			if calls == 0 || calls != cleanups {
+				t.Errorf("mismatched cleanups; got %d want %d", cleanups, calls)
+			}
+		},
+	}}
+	for _, tc := range testCases {
+		t.Run(tc.desc, func(t *T) {
+			var ok bool
+			buf := &bytes.Buffer{}
+			// This is almost like the Benchmark function, except that we override
+			// the benchtime and catch the failure result of the subbenchmark.
+			root := &B{
+				common: common{
+					signal: make(chan bool),
+					name:   "root",
+					w:      buf,
+				},
+				benchFunc: func(b *B) { ok = b.Run("test", tc.f) }, // Use Run to catch failure.
+				benchTime: benchTimeFlag{d: 1 * time.Microsecond},
+			}
+			if tc.chatty {
+				root.chatty = newChattyPrinter(root.w)
+			}
+			root.runN(1)
+			if ok != !tc.failed {
+				t.Errorf("%s:ok: got %v; want %v", tc.desc, ok, !tc.failed)
+			}
+			if !ok != root.Failed() {
+				t.Errorf("%s:root failed: got %v; want %v", tc.desc, !ok, root.Failed())
+			}
+			// All tests are run as subtests
+			if root.result.N != 1 {
+				t.Errorf("%s: N for parent benchmark was %d; want 1", tc.desc, root.result.N)
+			}
+			got := strings.TrimSpace(buf.String())
+			want := strings.TrimSpace(tc.output)
+			re := makeRegexp(want)
+			if ok, err := regexp.MatchString(re, got); !ok || err != nil {
+				t.Errorf("%s:output:\ngot:\n%s\nwant:\n%s", tc.desc, got, want)
+			}
+		})
+	}
+}
+
+func makeRegexp(s string) string {
+	s = regexp.QuoteMeta(s)
+	s = strings.ReplaceAll(s, ":NNN:", `:\d\d\d\d?:`)
+	s = strings.ReplaceAll(s, "N\\.NNs", `\d*\.\d*s`)
+	return s
+}
+
+func TestBenchmarkOutput(t *T) {
+	// Ensure Benchmark initialized common.w by invoking it with an error and
+	// normal case.
+	Benchmark(func(b *B) { b.Error("do not print this output") })
+	Benchmark(func(b *B) {})
+}
+
+func TestBenchmarkStartsFrom1(t *T) {
+	var first = true
+	Benchmark(func(b *B) {
+		if first && b.N != 1 {
+			panic(fmt.Sprintf("Benchmark() first N=%v; want 1", b.N))
+		}
+		first = false
+	})
+}
+
+func TestBenchmarkReadMemStatsBeforeFirstRun(t *T) {
+	var first = true
+	Benchmark(func(b *B) {
+		if first && (b.startAllocs == 0 || b.startBytes == 0) {
+			panic(fmt.Sprintf("ReadMemStats not called before first run"))
+		}
+		first = false
+	})
+}
+
+func TestParallelSub(t *T) {
+	c := make(chan int)
+	block := make(chan int)
+	for i := 0; i < 10; i++ {
+		go func(i int) {
+			<-block
+			t.Run(fmt.Sprint(i), func(t *T) {})
+			c <- 1
+		}(i)
+	}
+	close(block)
+	for i := 0; i < 10; i++ {
+		<-c
+	}
+}
+
+type funcWriter struct {
+	write func([]byte) (int, error)
+}
+
+func (fw *funcWriter) Write(b []byte) (int, error) {
+	return fw.write(b)
+}
+
+func TestRacyOutput(t *T) {
+	var runs int32  // The number of running Writes
+	var races int32 // Incremented for each race detected
+	raceDetector := func(b []byte) (int, error) {
+		// Check if some other goroutine is concurrently calling Write.
+		if atomic.LoadInt32(&runs) > 0 {
+			atomic.AddInt32(&races, 1) // Race detected!
+		}
+		atomic.AddInt32(&runs, 1)
+		defer atomic.AddInt32(&runs, -1)
+		runtime.Gosched() // Increase probability of a race
+		return len(b), nil
+	}
+
+	var wg sync.WaitGroup
+	root := &T{
+		common:  common{w: &funcWriter{raceDetector}},
+		context: newTestContext(1, newMatcher(regexp.MatchString, "", "")),
+	}
+	root.chatty = newChattyPrinter(root.w)
+	root.Run("", func(t *T) {
+		for i := 0; i < 100; i++ {
+			wg.Add(1)
+			go func(i int) {
+				defer wg.Done()
+				t.Run(fmt.Sprint(i), func(t *T) {
+					t.Logf("testing run %d", i)
+				})
+			}(i)
+		}
+	})
+	wg.Wait()
+
+	if races > 0 {
+		t.Errorf("detected %d racy Writes", races)
+	}
+}
+
+// The late log message did not include the test name.  Issue 29388.
+func TestLogAfterComplete(t *T) {
+	ctx := newTestContext(1, newMatcher(regexp.MatchString, "", ""))
+	var buf bytes.Buffer
+	t1 := &T{
+		common: common{
+			// Use a buffered channel so that tRunner can write
+			// to it although nothing is reading from it.
+			signal: make(chan bool, 1),
+			w:      &buf,
+		},
+		context: ctx,
+	}
+
+	c1 := make(chan bool)
+	c2 := make(chan string)
+	tRunner(t1, func(t *T) {
+		t.Run("TestLateLog", func(t *T) {
+			go func() {
+				defer close(c2)
+				defer func() {
+					p := recover()
+					if p == nil {
+						c2 <- "subtest did not panic"
+						return
+					}
+					s, ok := p.(string)
+					if !ok {
+						c2 <- fmt.Sprintf("subtest panic with unexpected value %v", p)
+						return
+					}
+					const want = "Log in goroutine after TestLateLog has completed"
+					if !strings.Contains(s, want) {
+						c2 <- fmt.Sprintf("subtest panic %q does not contain %q", s, want)
+					}
+				}()
+
+				<-c1
+				t.Log("log after test")
+			}()
+		})
+	})
+	close(c1)
+
+	if s := <-c2; s != "" {
+		t.Error(s)
+	}
+}
+
+func TestBenchmark(t *T) {
+	if Short() {
+		t.Skip("skipping in short mode")
+	}
+	res := Benchmark(func(b *B) {
+		for i := 0; i < 5; i++ {
+			b.Run("", func(b *B) {
+				for i := 0; i < b.N; i++ {
+					time.Sleep(time.Millisecond)
+				}
+			})
+		}
+	})
+	if res.NsPerOp() < 4000000 {
+		t.Errorf("want >5ms; got %v", time.Duration(res.NsPerOp()))
+	}
+}
+
+func TestCleanup(t *T) {
+	var cleanups []int
+	t.Run("test", func(t *T) {
+		t.Cleanup(func() { cleanups = append(cleanups, 1) })
+		t.Cleanup(func() { cleanups = append(cleanups, 2) })
+	})
+	if got, want := cleanups, []int{2, 1}; !reflect.DeepEqual(got, want) {
+		t.Errorf("unexpected cleanup record; got %v want %v", got, want)
+	}
+}
+
+func TestConcurrentCleanup(t *T) {
+	cleanups := 0
+	t.Run("test", func(t *T) {
+		done := make(chan struct{})
+		for i := 0; i < 2; i++ {
+			i := i
+			go func() {
+				t.Cleanup(func() {
+					cleanups |= 1 << i
+				})
+				done <- struct{}{}
+			}()
+		}
+		<-done
+		<-done
+	})
+	if cleanups != 1|2 {
+		t.Errorf("unexpected cleanup; got %d want 3", cleanups)
+	}
+}
+
+func TestCleanupCalledEvenAfterGoexit(t *T) {
+	cleanups := 0
+	t.Run("test", func(t *T) {
+		t.Cleanup(func() {
+			cleanups++
+		})
+		t.Cleanup(func() {
+			runtime.Goexit()
+		})
+	})
+	if cleanups != 1 {
+		t.Errorf("unexpected cleanup count; got %d want 1", cleanups)
+	}
+}
+
+func TestRunCleanup(t *T) {
+	outerCleanup := 0
+	innerCleanup := 0
+	t.Run("test", func(t *T) {
+		t.Cleanup(func() { outerCleanup++ })
+		t.Run("x", func(t *T) {
+			t.Cleanup(func() { innerCleanup++ })
+		})
+	})
+	if innerCleanup != 1 {
+		t.Errorf("unexpected inner cleanup count; got %d want 1", innerCleanup)
+	}
+	if outerCleanup != 1 {
+		t.Errorf("unexpected outer cleanup count; got %d want 0", outerCleanup)
+	}
+}
+
+func TestCleanupParallelSubtests(t *T) {
+	ranCleanup := 0
+	t.Run("test", func(t *T) {
+		t.Cleanup(func() { ranCleanup++ })
+		t.Run("x", func(t *T) {
+			t.Parallel()
+			if ranCleanup > 0 {
+				t.Error("outer cleanup ran before parallel subtest")
+			}
+		})
+	})
+	if ranCleanup != 1 {
+		t.Errorf("unexpected cleanup count; got %d want 1", ranCleanup)
+	}
+}
+
+func TestNestedCleanup(t *T) {
+	ranCleanup := 0
+	t.Run("test", func(t *T) {
+		t.Cleanup(func() {
+			if ranCleanup != 2 {
+				t.Errorf("unexpected cleanup count in first cleanup: got %d want 2", ranCleanup)
+			}
+			ranCleanup++
+		})
+		t.Cleanup(func() {
+			if ranCleanup != 0 {
+				t.Errorf("unexpected cleanup count in second cleanup: got %d want 0", ranCleanup)
+			}
+			ranCleanup++
+			t.Cleanup(func() {
+				if ranCleanup != 1 {
+					t.Errorf("unexpected cleanup count in nested cleanup: got %d want 1", ranCleanup)
+				}
+				ranCleanup++
+			})
+		})
+	})
+	if ranCleanup != 3 {
+		t.Errorf("unexpected cleanup count: got %d want 3", ranCleanup)
+	}
+}
diff --git a/src/testing/testing.go b/src/testing/testing.go
new file mode 100644
index 0000000..dec39d2
--- /dev/null
+++ b/src/testing/testing.go
@@ -0,0 +1,1732 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package testing provides support for automated testing of Go packages.
+// It is intended to be used in concert with the "go test" command, which automates
+// execution of any function of the form
+//     func TestXxx(*testing.T)
+// where Xxx does not start with a lowercase letter. The function name
+// serves to identify the test routine.
+//
+// Within these functions, use the Error, Fail or related methods to signal failure.
+//
+// To write a new test suite, create a file whose name ends _test.go that
+// contains the TestXxx functions as described here. Put the file in the same
+// package as the one being tested. The file will be excluded from regular
+// package builds but will be included when the "go test" command is run.
+// For more detail, run "go help test" and "go help testflag".
+//
+// A simple test function looks like this:
+//
+//     func TestAbs(t *testing.T) {
+//         got := Abs(-1)
+//         if got != 1 {
+//             t.Errorf("Abs(-1) = %d; want 1", got)
+//         }
+//     }
+//
+// Benchmarks
+//
+// Functions of the form
+//     func BenchmarkXxx(*testing.B)
+// are considered benchmarks, and are executed by the "go test" command when
+// its -bench flag is provided. Benchmarks are run sequentially.
+//
+// For a description of the testing flags, see
+// https://golang.org/cmd/go/#hdr-Testing_flags
+//
+// A sample benchmark function looks like this:
+//     func BenchmarkRandInt(b *testing.B) {
+//         for i := 0; i < b.N; i++ {
+//             rand.Int()
+//         }
+//     }
+//
+// The benchmark function must run the target code b.N times.
+// During benchmark execution, b.N is adjusted until the benchmark function lasts
+// long enough to be timed reliably. The output
+//     BenchmarkRandInt-8   	68453040	        17.8 ns/op
+// means that the loop ran 68453040 times at a speed of 17.8 ns per loop.
+//
+// If a benchmark needs some expensive setup before running, the timer
+// may be reset:
+//
+//     func BenchmarkBigLen(b *testing.B) {
+//         big := NewBig()
+//         b.ResetTimer()
+//         for i := 0; i < b.N; i++ {
+//             big.Len()
+//         }
+//     }
+//
+// If a benchmark needs to test performance in a parallel setting, it may use
+// the RunParallel helper function; such benchmarks are intended to be used with
+// the go test -cpu flag:
+//
+//     func BenchmarkTemplateParallel(b *testing.B) {
+//         templ := template.Must(template.New("test").Parse("Hello, {{.}}!"))
+//         b.RunParallel(func(pb *testing.PB) {
+//             var buf bytes.Buffer
+//             for pb.Next() {
+//                 buf.Reset()
+//                 templ.Execute(&buf, "World")
+//             }
+//         })
+//     }
+//
+// Examples
+//
+// The package also runs and verifies example code. Example functions may
+// include a concluding line comment that begins with "Output:" and is compared with
+// the standard output of the function when the tests are run. (The comparison
+// ignores leading and trailing space.) These are examples of an example:
+//
+//     func ExampleHello() {
+//         fmt.Println("hello")
+//         // Output: hello
+//     }
+//
+//     func ExampleSalutations() {
+//         fmt.Println("hello, and")
+//         fmt.Println("goodbye")
+//         // Output:
+//         // hello, and
+//         // goodbye
+//     }
+//
+// The comment prefix "Unordered output:" is like "Output:", but matches any
+// line order:
+//
+//     func ExamplePerm() {
+//         for _, value := range Perm(5) {
+//             fmt.Println(value)
+//         }
+//         // Unordered output: 4
+//         // 2
+//         // 1
+//         // 3
+//         // 0
+//     }
+//
+// Example functions without output comments are compiled but not executed.
+//
+// The naming convention to declare examples for the package, a function F, a type T and
+// method M on type T are:
+//
+//     func Example() { ... }
+//     func ExampleF() { ... }
+//     func ExampleT() { ... }
+//     func ExampleT_M() { ... }
+//
+// Multiple example functions for a package/type/function/method may be provided by
+// appending a distinct suffix to the name. The suffix must start with a
+// lower-case letter.
+//
+//     func Example_suffix() { ... }
+//     func ExampleF_suffix() { ... }
+//     func ExampleT_suffix() { ... }
+//     func ExampleT_M_suffix() { ... }
+//
+// The entire test file is presented as the example when it contains a single
+// example function, at least one other function, type, variable, or constant
+// declaration, and no test or benchmark functions.
+//
+// Skipping
+//
+// Tests or benchmarks may be skipped at run time with a call to
+// the Skip method of *T or *B:
+//
+//     func TestTimeConsuming(t *testing.T) {
+//         if testing.Short() {
+//             t.Skip("skipping test in short mode.")
+//         }
+//         ...
+//     }
+//
+// Subtests and Sub-benchmarks
+//
+// The Run methods of T and B allow defining subtests and sub-benchmarks,
+// without having to define separate functions for each. This enables uses
+// like table-driven benchmarks and creating hierarchical tests.
+// It also provides a way to share common setup and tear-down code:
+//
+//     func TestFoo(t *testing.T) {
+//         // <setup code>
+//         t.Run("A=1", func(t *testing.T) { ... })
+//         t.Run("A=2", func(t *testing.T) { ... })
+//         t.Run("B=1", func(t *testing.T) { ... })
+//         // <tear-down code>
+//     }
+//
+// Each subtest and sub-benchmark has a unique name: the combination of the name
+// of the top-level test and the sequence of names passed to Run, separated by
+// slashes, with an optional trailing sequence number for disambiguation.
+//
+// The argument to the -run and -bench command-line flags is an unanchored regular
+// expression that matches the test's name. For tests with multiple slash-separated
+// elements, such as subtests, the argument is itself slash-separated, with
+// expressions matching each name element in turn. Because it is unanchored, an
+// empty expression matches any string.
+// For example, using "matching" to mean "whose name contains":
+//
+//     go test -run ''      # Run all tests.
+//     go test -run Foo     # Run top-level tests matching "Foo", such as "TestFooBar".
+//     go test -run Foo/A=  # For top-level tests matching "Foo", run subtests matching "A=".
+//     go test -run /A=1    # For all top-level tests, run subtests matching "A=1".
+//
+// Subtests can also be used to control parallelism. A parent test will only
+// complete once all of its subtests complete. In this example, all tests are
+// run in parallel with each other, and only with each other, regardless of
+// other top-level tests that may be defined:
+//
+//     func TestGroupedParallel(t *testing.T) {
+//         for _, tc := range tests {
+//             tc := tc // capture range variable
+//             t.Run(tc.Name, func(t *testing.T) {
+//                 t.Parallel()
+//                 ...
+//             })
+//         }
+//     }
+//
+// The race detector kills the program if it exceeds 8192 concurrent goroutines,
+// so use care when running parallel tests with the -race flag set.
+//
+// Run does not return until parallel subtests have completed, providing a way
+// to clean up after a group of parallel tests:
+//
+//     func TestTeardownParallel(t *testing.T) {
+//         // This Run will not return until the parallel tests finish.
+//         t.Run("group", func(t *testing.T) {
+//             t.Run("Test1", parallelTest1)
+//             t.Run("Test2", parallelTest2)
+//             t.Run("Test3", parallelTest3)
+//         })
+//         // <tear-down code>
+//     }
+//
+// Main
+//
+// It is sometimes necessary for a test program to do extra setup or teardown
+// before or after testing. It is also sometimes necessary for a test to control
+// which code runs on the main thread. To support these and other cases,
+// if a test file contains a function:
+//
+//	func TestMain(m *testing.M)
+//
+// then the generated test will call TestMain(m) instead of running the tests
+// directly. TestMain runs in the main goroutine and can do whatever setup
+// and teardown is necessary around a call to m.Run. m.Run will return an exit
+// code that may be passed to os.Exit. If TestMain returns, the test wrapper
+// will pass the result of m.Run to os.Exit itself.
+//
+// When TestMain is called, flag.Parse has not been run. If TestMain depends on
+// command-line flags, including those of the testing package, it should call
+// flag.Parse explicitly. Command line flags are always parsed by the time test
+// or benchmark functions run.
+//
+// A simple implementation of TestMain is:
+//
+//	func TestMain(m *testing.M) {
+//		// call flag.Parse() here if TestMain uses flags
+//		os.Exit(m.Run())
+//	}
+//
+package testing
+
+import (
+	"bytes"
+	"errors"
+	"flag"
+	"fmt"
+	"internal/race"
+	"io"
+	"os"
+	"runtime"
+	"runtime/debug"
+	"runtime/trace"
+	"strconv"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+var initRan bool
+
+// Init registers testing flags. These flags are automatically registered by
+// the "go test" command before running test functions, so Init is only needed
+// when calling functions such as Benchmark without using "go test".
+//
+// Init has no effect if it was already called.
+func Init() {
+	if initRan {
+		return
+	}
+	initRan = true
+	// The short flag requests that tests run more quickly, but its functionality
+	// is provided by test writers themselves. The testing package is just its
+	// home. The all.bash installation script sets it to make installation more
+	// efficient, but by default the flag is off so a plain "go test" will do a
+	// full test of the package.
+	short = flag.Bool("test.short", false, "run smaller test suite to save time")
+
+	// The failfast flag requests that test execution stop after the first test failure.
+	failFast = flag.Bool("test.failfast", false, "do not start new tests after the first test failure")
+
+	// The directory in which to create profile files and the like. When run from
+	// "go test", the binary always runs in the source directory for the package;
+	// this flag lets "go test" tell the binary to write the files in the directory where
+	// the "go test" command is run.
+	outputDir = flag.String("test.outputdir", "", "write profiles to `dir`")
+	// Report as tests are run; default is silent for success.
+	chatty = flag.Bool("test.v", false, "verbose: print additional output")
+	count = flag.Uint("test.count", 1, "run tests and benchmarks `n` times")
+	coverProfile = flag.String("test.coverprofile", "", "write a coverage profile to `file`")
+	matchList = flag.String("test.list", "", "list tests, examples, and benchmarks matching `regexp` then exit")
+	match = flag.String("test.run", "", "run only tests and examples matching `regexp`")
+	memProfile = flag.String("test.memprofile", "", "write an allocation profile to `file`")
+	memProfileRate = flag.Int("test.memprofilerate", 0, "set memory allocation profiling `rate` (see runtime.MemProfileRate)")
+	cpuProfile = flag.String("test.cpuprofile", "", "write a cpu profile to `file`")
+	blockProfile = flag.String("test.blockprofile", "", "write a goroutine blocking profile to `file`")
+	blockProfileRate = flag.Int("test.blockprofilerate", 1, "set blocking profile `rate` (see runtime.SetBlockProfileRate)")
+	mutexProfile = flag.String("test.mutexprofile", "", "write a mutex contention profile to the named file after execution")
+	mutexProfileFraction = flag.Int("test.mutexprofilefraction", 1, "if >= 0, calls runtime.SetMutexProfileFraction()")
+	panicOnExit0 = flag.Bool("test.paniconexit0", false, "panic on call to os.Exit(0)")
+	traceFile = flag.String("test.trace", "", "write an execution trace to `file`")
+	timeout = flag.Duration("test.timeout", 0, "panic test binary after duration `d` (default 0, timeout disabled)")
+	cpuListStr = flag.String("test.cpu", "", "comma-separated `list` of cpu counts to run each test with")
+	parallel = flag.Int("test.parallel", runtime.GOMAXPROCS(0), "run at most `n` tests in parallel")
+	testlog = flag.String("test.testlogfile", "", "write test action log to `file` (for use only by cmd/go)")
+
+	initBenchmarkFlags()
+}
+
+var (
+	// Flags, registered during Init.
+	short                *bool
+	failFast             *bool
+	outputDir            *string
+	chatty               *bool
+	count                *uint
+	coverProfile         *string
+	matchList            *string
+	match                *string
+	memProfile           *string
+	memProfileRate       *int
+	cpuProfile           *string
+	blockProfile         *string
+	blockProfileRate     *int
+	mutexProfile         *string
+	mutexProfileFraction *int
+	panicOnExit0         *bool
+	traceFile            *string
+	timeout              *time.Duration
+	cpuListStr           *string
+	parallel             *int
+	testlog              *string
+
+	haveExamples bool // are there examples?
+
+	cpuList     []int
+	testlogFile *os.File
+
+	numFailed uint32 // number of test failures
+)
+
+type chattyPrinter struct {
+	w          io.Writer
+	lastNameMu sync.Mutex // guards lastName
+	lastName   string     // last printed test name in chatty mode
+}
+
+func newChattyPrinter(w io.Writer) *chattyPrinter {
+	return &chattyPrinter{w: w}
+}
+
+// Updatef prints a message about the status of the named test to w.
+//
+// The formatted message must include the test name itself.
+func (p *chattyPrinter) Updatef(testName, format string, args ...interface{}) {
+	p.lastNameMu.Lock()
+	defer p.lastNameMu.Unlock()
+
+	// Since the message already implies an association with a specific new test,
+	// we don't need to check what the old test name was or log an extra CONT line
+	// for it. (We're updating it anyway, and the current message already includes
+	// the test name.)
+	p.lastName = testName
+	fmt.Fprintf(p.w, format, args...)
+}
+
+// Printf prints a message, generated by the named test, that does not
+// necessarily mention that tests's name itself.
+func (p *chattyPrinter) Printf(testName, format string, args ...interface{}) {
+	p.lastNameMu.Lock()
+	defer p.lastNameMu.Unlock()
+
+	if p.lastName == "" {
+		p.lastName = testName
+	} else if p.lastName != testName {
+		fmt.Fprintf(p.w, "=== CONT  %s\n", testName)
+		p.lastName = testName
+	}
+
+	fmt.Fprintf(p.w, format, args...)
+}
+
+// The maximum number of stack frames to go through when skipping helper functions for
+// the purpose of decorating log messages.
+const maxStackLen = 50
+
+// common holds the elements common between T and B and
+// captures common methods such as Errorf.
+type common struct {
+	mu          sync.RWMutex         // guards this group of fields
+	output      []byte               // Output generated by test or benchmark.
+	w           io.Writer            // For flushToParent.
+	ran         bool                 // Test or benchmark (or one of its subtests) was executed.
+	failed      bool                 // Test or benchmark has failed.
+	skipped     bool                 // Test of benchmark has been skipped.
+	done        bool                 // Test is finished and all subtests have completed.
+	helperPCs   map[uintptr]struct{} // functions to be skipped when writing file/line info
+	helperNames map[string]struct{}  // helperPCs converted to function names
+	cleanups    []func()             // optional functions to be called at the end of the test
+	cleanupName string               // Name of the cleanup function.
+	cleanupPc   []uintptr            // The stack trace at the point where Cleanup was called.
+
+	chatty     *chattyPrinter // A copy of chattyPrinter, if the chatty flag is set.
+	bench      bool           // Whether the current test is a benchmark.
+	finished   bool           // Test function has completed.
+	hasSub     int32          // Written atomically.
+	raceErrors int            // Number of races detected during test.
+	runner     string         // Function name of tRunner running the test.
+
+	parent   *common
+	level    int       // Nesting depth of test or benchmark.
+	creator  []uintptr // If level > 0, the stack trace at the point where the parent called t.Run.
+	name     string    // Name of test or benchmark.
+	start    time.Time // Time test or benchmark started
+	duration time.Duration
+	barrier  chan bool // To signal parallel subtests they may start.
+	signal   chan bool // To signal a test is done.
+	sub      []*T      // Queue of subtests to be run in parallel.
+
+	tempDirMu  sync.Mutex
+	tempDir    string
+	tempDirErr error
+	tempDirSeq int32
+}
+
+// Short reports whether the -test.short flag is set.
+func Short() bool {
+	if short == nil {
+		panic("testing: Short called before Init")
+	}
+	// Catch code that calls this from TestMain without first calling flag.Parse.
+	if !flag.Parsed() {
+		panic("testing: Short called before Parse")
+	}
+
+	return *short
+}
+
+// CoverMode reports what the test coverage mode is set to. The
+// values are "set", "count", or "atomic". The return value will be
+// empty if test coverage is not enabled.
+func CoverMode() string {
+	return cover.Mode
+}
+
+// Verbose reports whether the -test.v flag is set.
+func Verbose() bool {
+	// Same as in Short.
+	if chatty == nil {
+		panic("testing: Verbose called before Init")
+	}
+	if !flag.Parsed() {
+		panic("testing: Verbose called before Parse")
+	}
+	return *chatty
+}
+
+// frameSkip searches, starting after skip frames, for the first caller frame
+// in a function not marked as a helper and returns that frame.
+// The search stops if it finds a tRunner function that
+// was the entry point into the test and the test is not a subtest.
+// This function must be called with c.mu held.
+func (c *common) frameSkip(skip int) runtime.Frame {
+	// If the search continues into the parent test, we'll have to hold
+	// its mu temporarily. If we then return, we need to unlock it.
+	shouldUnlock := false
+	defer func() {
+		if shouldUnlock {
+			c.mu.Unlock()
+		}
+	}()
+	var pc [maxStackLen]uintptr
+	// Skip two extra frames to account for this function
+	// and runtime.Callers itself.
+	n := runtime.Callers(skip+2, pc[:])
+	if n == 0 {
+		panic("testing: zero callers found")
+	}
+	frames := runtime.CallersFrames(pc[:n])
+	var firstFrame, prevFrame, frame runtime.Frame
+	for more := true; more; prevFrame = frame {
+		frame, more = frames.Next()
+		if frame.Function == c.cleanupName {
+			frames = runtime.CallersFrames(c.cleanupPc)
+			continue
+		}
+		if firstFrame.PC == 0 {
+			firstFrame = frame
+		}
+		if frame.Function == c.runner {
+			// We've gone up all the way to the tRunner calling
+			// the test function (so the user must have
+			// called tb.Helper from inside that test function).
+			// If this is a top-level test, only skip up to the test function itself.
+			// If we're in a subtest, continue searching in the parent test,
+			// starting from the point of the call to Run which created this subtest.
+			if c.level > 1 {
+				frames = runtime.CallersFrames(c.creator)
+				parent := c.parent
+				// We're no longer looking at the current c after this point,
+				// so we should unlock its mu, unless it's the original receiver,
+				// in which case our caller doesn't expect us to do that.
+				if shouldUnlock {
+					c.mu.Unlock()
+				}
+				c = parent
+				// Remember to unlock c.mu when we no longer need it, either
+				// because we went up another nesting level, or because we
+				// returned.
+				shouldUnlock = true
+				c.mu.Lock()
+				continue
+			}
+			return prevFrame
+		}
+		// If more helper PCs have been added since we last did the conversion
+		if c.helperNames == nil {
+			c.helperNames = make(map[string]struct{})
+			for pc := range c.helperPCs {
+				c.helperNames[pcToName(pc)] = struct{}{}
+			}
+		}
+		if _, ok := c.helperNames[frame.Function]; !ok {
+			// Found a frame that wasn't inside a helper function.
+			return frame
+		}
+	}
+	return firstFrame
+}
+
+// decorate prefixes the string with the file and line of the call site
+// and inserts the final newline if needed and indentation spaces for formatting.
+// This function must be called with c.mu held.
+func (c *common) decorate(s string, skip int) string {
+	frame := c.frameSkip(skip)
+	file := frame.File
+	line := frame.Line
+	if file != "" {
+		// Truncate file name at last file name separator.
+		if index := strings.LastIndex(file, "/"); index >= 0 {
+			file = file[index+1:]
+		} else if index = strings.LastIndex(file, "\\"); index >= 0 {
+			file = file[index+1:]
+		}
+	} else {
+		file = "???"
+	}
+	if line == 0 {
+		line = 1
+	}
+	buf := new(strings.Builder)
+	// Every line is indented at least 4 spaces.
+	buf.WriteString("    ")
+	fmt.Fprintf(buf, "%s:%d: ", file, line)
+	lines := strings.Split(s, "\n")
+	if l := len(lines); l > 1 && lines[l-1] == "" {
+		lines = lines[:l-1]
+	}
+	for i, line := range lines {
+		if i > 0 {
+			// Second and subsequent lines are indented an additional 4 spaces.
+			buf.WriteString("\n        ")
+		}
+		buf.WriteString(line)
+	}
+	buf.WriteByte('\n')
+	return buf.String()
+}
+
+// flushToParent writes c.output to the parent after first writing the header
+// with the given format and arguments.
+func (c *common) flushToParent(testName, format string, args ...interface{}) {
+	p := c.parent
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if len(c.output) > 0 {
+		format += "%s"
+		args = append(args[:len(args):len(args)], c.output)
+		c.output = c.output[:0] // but why?
+	}
+
+	if c.chatty != nil && p.w == c.chatty.w {
+		// We're flushing to the actual output, so track that this output is
+		// associated with a specific test (and, specifically, that the next output
+		// is *not* associated with that test).
+		//
+		// Moreover, if c.output is non-empty it is important that this write be
+		// atomic with respect to the output of other tests, so that we don't end up
+		// with confusing '=== CONT' lines in the middle of our '--- PASS' block.
+		// Neither humans nor cmd/test2json can parse those easily.
+		// (See https://golang.org/issue/40771.)
+		c.chatty.Updatef(testName, format, args...)
+	} else {
+		// We're flushing to the output buffer of the parent test, which will
+		// itself follow a test-name header when it is finally flushed to stdout.
+		fmt.Fprintf(p.w, format, args...)
+	}
+}
+
+type indenter struct {
+	c *common
+}
+
+func (w indenter) Write(b []byte) (n int, err error) {
+	n = len(b)
+	for len(b) > 0 {
+		end := bytes.IndexByte(b, '\n')
+		if end == -1 {
+			end = len(b)
+		} else {
+			end++
+		}
+		// An indent of 4 spaces will neatly align the dashes with the status
+		// indicator of the parent.
+		const indent = "    "
+		w.c.output = append(w.c.output, indent...)
+		w.c.output = append(w.c.output, b[:end]...)
+		b = b[end:]
+	}
+	return
+}
+
+// fmtDuration returns a string representing d in the form "87.00s".
+func fmtDuration(d time.Duration) string {
+	return fmt.Sprintf("%.2fs", d.Seconds())
+}
+
+// TB is the interface common to T and B.
+type TB interface {
+	Cleanup(func())
+	Error(args ...interface{})
+	Errorf(format string, args ...interface{})
+	Fail()
+	FailNow()
+	Failed() bool
+	Fatal(args ...interface{})
+	Fatalf(format string, args ...interface{})
+	Helper()
+	Log(args ...interface{})
+	Logf(format string, args ...interface{})
+	Name() string
+	Skip(args ...interface{})
+	SkipNow()
+	Skipf(format string, args ...interface{})
+	Skipped() bool
+	TempDir() string
+
+	// A private method to prevent users implementing the
+	// interface and so future additions to it will not
+	// violate Go 1 compatibility.
+	private()
+}
+
+var _ TB = (*T)(nil)
+var _ TB = (*B)(nil)
+
+// T is a type passed to Test functions to manage test state and support formatted test logs.
+//
+// A test ends when its Test function returns or calls any of the methods
+// FailNow, Fatal, Fatalf, SkipNow, Skip, or Skipf. Those methods, as well as
+// the Parallel method, must be called only from the goroutine running the
+// Test function.
+//
+// The other reporting methods, such as the variations of Log and Error,
+// may be called simultaneously from multiple goroutines.
+type T struct {
+	common
+	isParallel bool
+	context    *testContext // For running tests and subtests.
+}
+
+func (c *common) private() {}
+
+// Name returns the name of the running test or benchmark.
+func (c *common) Name() string {
+	return c.name
+}
+
+func (c *common) setRan() {
+	if c.parent != nil {
+		c.parent.setRan()
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.ran = true
+}
+
+// Fail marks the function as having failed but continues execution.
+func (c *common) Fail() {
+	if c.parent != nil {
+		c.parent.Fail()
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	// c.done needs to be locked to synchronize checks to c.done in parent tests.
+	if c.done {
+		panic("Fail in goroutine after " + c.name + " has completed")
+	}
+	c.failed = true
+}
+
+// Failed reports whether the function has failed.
+func (c *common) Failed() bool {
+	c.mu.RLock()
+	failed := c.failed
+	c.mu.RUnlock()
+	return failed || c.raceErrors+race.Errors() > 0
+}
+
+// FailNow marks the function as having failed and stops its execution
+// by calling runtime.Goexit (which then runs all deferred calls in the
+// current goroutine).
+// Execution will continue at the next test or benchmark.
+// FailNow must be called from the goroutine running the
+// test or benchmark function, not from other goroutines
+// created during the test. Calling FailNow does not stop
+// those other goroutines.
+func (c *common) FailNow() {
+	c.Fail()
+
+	// Calling runtime.Goexit will exit the goroutine, which
+	// will run the deferred functions in this goroutine,
+	// which will eventually run the deferred lines in tRunner,
+	// which will signal to the test loop that this test is done.
+	//
+	// A previous version of this code said:
+	//
+	//	c.duration = ...
+	//	c.signal <- c.self
+	//	runtime.Goexit()
+	//
+	// This previous version duplicated code (those lines are in
+	// tRunner no matter what), but worse the goroutine teardown
+	// implicit in runtime.Goexit was not guaranteed to complete
+	// before the test exited. If a test deferred an important cleanup
+	// function (like removing temporary files), there was no guarantee
+	// it would run on a test failure. Because we send on c.signal during
+	// a top-of-stack deferred function now, we know that the send
+	// only happens after any other stacked defers have completed.
+	c.finished = true
+	runtime.Goexit()
+}
+
+// log generates the output. It's always at the same stack depth.
+func (c *common) log(s string) {
+	c.logDepth(s, 3) // logDepth + log + public function
+}
+
+// logDepth generates the output at an arbitrary stack depth.
+func (c *common) logDepth(s string, depth int) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.done {
+		// This test has already finished. Try and log this message
+		// with our parent. If we don't have a parent, panic.
+		for parent := c.parent; parent != nil; parent = parent.parent {
+			parent.mu.Lock()
+			defer parent.mu.Unlock()
+			if !parent.done {
+				parent.output = append(parent.output, parent.decorate(s, depth+1)...)
+				return
+			}
+		}
+		panic("Log in goroutine after " + c.name + " has completed")
+	} else {
+		if c.chatty != nil {
+			if c.bench {
+				// Benchmarks don't print === CONT, so we should skip the test
+				// printer and just print straight to stdout.
+				fmt.Print(c.decorate(s, depth+1))
+			} else {
+				c.chatty.Printf(c.name, "%s", c.decorate(s, depth+1))
+			}
+
+			return
+		}
+		c.output = append(c.output, c.decorate(s, depth+1)...)
+	}
+}
+
+// Log formats its arguments using default formatting, analogous to Println,
+// and records the text in the error log. For tests, the text will be printed only if
+// the test fails or the -test.v flag is set. For benchmarks, the text is always
+// printed to avoid having performance depend on the value of the -test.v flag.
+func (c *common) Log(args ...interface{}) { c.log(fmt.Sprintln(args...)) }
+
+// Logf formats its arguments according to the format, analogous to Printf, and
+// records the text in the error log. A final newline is added if not provided. For
+// tests, the text will be printed only if the test fails or the -test.v flag is
+// set. For benchmarks, the text is always printed to avoid having performance
+// depend on the value of the -test.v flag.
+func (c *common) Logf(format string, args ...interface{}) { c.log(fmt.Sprintf(format, args...)) }
+
+// Error is equivalent to Log followed by Fail.
+func (c *common) Error(args ...interface{}) {
+	c.log(fmt.Sprintln(args...))
+	c.Fail()
+}
+
+// Errorf is equivalent to Logf followed by Fail.
+func (c *common) Errorf(format string, args ...interface{}) {
+	c.log(fmt.Sprintf(format, args...))
+	c.Fail()
+}
+
+// Fatal is equivalent to Log followed by FailNow.
+func (c *common) Fatal(args ...interface{}) {
+	c.log(fmt.Sprintln(args...))
+	c.FailNow()
+}
+
+// Fatalf is equivalent to Logf followed by FailNow.
+func (c *common) Fatalf(format string, args ...interface{}) {
+	c.log(fmt.Sprintf(format, args...))
+	c.FailNow()
+}
+
+// Skip is equivalent to Log followed by SkipNow.
+func (c *common) Skip(args ...interface{}) {
+	c.log(fmt.Sprintln(args...))
+	c.SkipNow()
+}
+
+// Skipf is equivalent to Logf followed by SkipNow.
+func (c *common) Skipf(format string, args ...interface{}) {
+	c.log(fmt.Sprintf(format, args...))
+	c.SkipNow()
+}
+
+// SkipNow marks the test as having been skipped and stops its execution
+// by calling runtime.Goexit.
+// If a test fails (see Error, Errorf, Fail) and is then skipped,
+// it is still considered to have failed.
+// Execution will continue at the next test or benchmark. See also FailNow.
+// SkipNow must be called from the goroutine running the test, not from
+// other goroutines created during the test. Calling SkipNow does not stop
+// those other goroutines.
+func (c *common) SkipNow() {
+	c.skip()
+	c.finished = true
+	runtime.Goexit()
+}
+
+func (c *common) skip() {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.skipped = true
+}
+
+// Skipped reports whether the test was skipped.
+func (c *common) Skipped() bool {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return c.skipped
+}
+
+// Helper marks the calling function as a test helper function.
+// When printing file and line information, that function will be skipped.
+// Helper may be called simultaneously from multiple goroutines.
+func (c *common) Helper() {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.helperPCs == nil {
+		c.helperPCs = make(map[uintptr]struct{})
+	}
+	// repeating code from callerName here to save walking a stack frame
+	var pc [1]uintptr
+	n := runtime.Callers(2, pc[:]) // skip runtime.Callers + Helper
+	if n == 0 {
+		panic("testing: zero callers found")
+	}
+	if _, found := c.helperPCs[pc[0]]; !found {
+		c.helperPCs[pc[0]] = struct{}{}
+		c.helperNames = nil // map will be recreated next time it is needed
+	}
+}
+
+// Cleanup registers a function to be called when the test and all its
+// subtests complete. Cleanup functions will be called in last added,
+// first called order.
+func (c *common) Cleanup(f func()) {
+	var pc [maxStackLen]uintptr
+	// Skip two extra frames to account for this function and runtime.Callers itself.
+	n := runtime.Callers(2, pc[:])
+	cleanupPc := pc[:n]
+
+	fn := func() {
+		defer func() {
+			c.mu.Lock()
+			defer c.mu.Unlock()
+			c.cleanupName = ""
+			c.cleanupPc = nil
+		}()
+
+		name := callerName(0)
+		c.mu.Lock()
+		c.cleanupName = name
+		c.cleanupPc = cleanupPc
+		c.mu.Unlock()
+
+		f()
+	}
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.cleanups = append(c.cleanups, fn)
+}
+
+var tempDirReplacer struct {
+	sync.Once
+	r *strings.Replacer
+}
+
+// TempDir returns a temporary directory for the test to use.
+// The directory is automatically removed by Cleanup when the test and
+// all its subtests complete.
+// Each subsequent call to t.TempDir returns a unique directory;
+// if the directory creation fails, TempDir terminates the test by calling Fatal.
+func (c *common) TempDir() string {
+	// Use a single parent directory for all the temporary directories
+	// created by a test, each numbered sequentially.
+	c.tempDirMu.Lock()
+	var nonExistent bool
+	if c.tempDir == "" { // Usually the case with js/wasm
+		nonExistent = true
+	} else {
+		_, err := os.Stat(c.tempDir)
+		nonExistent = os.IsNotExist(err)
+		if err != nil && !nonExistent {
+			c.Fatalf("TempDir: %v", err)
+		}
+	}
+
+	if nonExistent {
+		c.Helper()
+
+		// os.MkdirTemp doesn't like path separators in its pattern,
+		// so mangle the name to accommodate subtests.
+		tempDirReplacer.Do(func() {
+			tempDirReplacer.r = strings.NewReplacer("/", "_", "\\", "_", ":", "_")
+		})
+		pattern := tempDirReplacer.r.Replace(c.Name())
+
+		c.tempDir, c.tempDirErr = os.MkdirTemp("", pattern)
+		if c.tempDirErr == nil {
+			c.Cleanup(func() {
+				if err := os.RemoveAll(c.tempDir); err != nil {
+					c.Errorf("TempDir RemoveAll cleanup: %v", err)
+				}
+			})
+		}
+	}
+	c.tempDirMu.Unlock()
+
+	if c.tempDirErr != nil {
+		c.Fatalf("TempDir: %v", c.tempDirErr)
+	}
+	seq := atomic.AddInt32(&c.tempDirSeq, 1)
+	dir := fmt.Sprintf("%s%c%03d", c.tempDir, os.PathSeparator, seq)
+	if err := os.Mkdir(dir, 0777); err != nil {
+		c.Fatalf("TempDir: %v", err)
+	}
+	return dir
+}
+
+// panicHanding is an argument to runCleanup.
+type panicHandling int
+
+const (
+	normalPanic panicHandling = iota
+	recoverAndReturnPanic
+)
+
+// runCleanup is called at the end of the test.
+// If catchPanic is true, this will catch panics, and return the recovered
+// value if any.
+func (c *common) runCleanup(ph panicHandling) (panicVal interface{}) {
+	if ph == recoverAndReturnPanic {
+		defer func() {
+			panicVal = recover()
+		}()
+	}
+
+	// Make sure that if a cleanup function panics,
+	// we still run the remaining cleanup functions.
+	defer func() {
+		c.mu.Lock()
+		recur := len(c.cleanups) > 0
+		c.mu.Unlock()
+		if recur {
+			c.runCleanup(normalPanic)
+		}
+	}()
+
+	for {
+		var cleanup func()
+		c.mu.Lock()
+		if len(c.cleanups) > 0 {
+			last := len(c.cleanups) - 1
+			cleanup = c.cleanups[last]
+			c.cleanups = c.cleanups[:last]
+		}
+		c.mu.Unlock()
+		if cleanup == nil {
+			return nil
+		}
+		cleanup()
+	}
+}
+
+// callerName gives the function name (qualified with a package path)
+// for the caller after skip frames (where 0 means the current function).
+func callerName(skip int) string {
+	var pc [1]uintptr
+	n := runtime.Callers(skip+2, pc[:]) // skip + runtime.Callers + callerName
+	if n == 0 {
+		panic("testing: zero callers found")
+	}
+	return pcToName(pc[0])
+}
+
+func pcToName(pc uintptr) string {
+	pcs := []uintptr{pc}
+	frames := runtime.CallersFrames(pcs)
+	frame, _ := frames.Next()
+	return frame.Function
+}
+
+// Parallel signals that this test is to be run in parallel with (and only with)
+// other parallel tests. When a test is run multiple times due to use of
+// -test.count or -test.cpu, multiple instances of a single test never run in
+// parallel with each other.
+func (t *T) Parallel() {
+	if t.isParallel {
+		panic("testing: t.Parallel called multiple times")
+	}
+	t.isParallel = true
+
+	// We don't want to include the time we spend waiting for serial tests
+	// in the test duration. Record the elapsed time thus far and reset the
+	// timer afterwards.
+	t.duration += time.Since(t.start)
+
+	// Add to the list of tests to be released by the parent.
+	t.parent.sub = append(t.parent.sub, t)
+	t.raceErrors += race.Errors()
+
+	if t.chatty != nil {
+		// Unfortunately, even though PAUSE indicates that the named test is *no
+		// longer* running, cmd/test2json interprets it as changing the active test
+		// for the purpose of log parsing. We could fix cmd/test2json, but that
+		// won't fix existing deployments of third-party tools that already shell
+		// out to older builds of cmd/test2json — so merely fixing cmd/test2json
+		// isn't enough for now.
+		t.chatty.Updatef(t.name, "=== PAUSE %s\n", t.name)
+	}
+
+	t.signal <- true   // Release calling test.
+	<-t.parent.barrier // Wait for the parent test to complete.
+	t.context.waitParallel()
+
+	if t.chatty != nil {
+		t.chatty.Updatef(t.name, "=== CONT  %s\n", t.name)
+	}
+
+	t.start = time.Now()
+	t.raceErrors += -race.Errors()
+}
+
+// InternalTest is an internal type but exported because it is cross-package;
+// it is part of the implementation of the "go test" command.
+type InternalTest struct {
+	Name string
+	F    func(*T)
+}
+
+var errNilPanicOrGoexit = errors.New("test executed panic(nil) or runtime.Goexit")
+
+func tRunner(t *T, fn func(t *T)) {
+	t.runner = callerName(0)
+
+	// When this goroutine is done, either because fn(t)
+	// returned normally or because a test failure triggered
+	// a call to runtime.Goexit, record the duration and send
+	// a signal saying that the test is done.
+	defer func() {
+		if t.Failed() {
+			atomic.AddUint32(&numFailed, 1)
+		}
+
+		if t.raceErrors+race.Errors() > 0 {
+			t.Errorf("race detected during execution of test")
+		}
+
+		// If the test panicked, print any test output before dying.
+		err := recover()
+		signal := true
+
+		if !t.finished && err == nil {
+			err = errNilPanicOrGoexit
+			for p := t.parent; p != nil; p = p.parent {
+				if p.finished {
+					t.Errorf("%v: subtest may have called FailNow on a parent test", err)
+					err = nil
+					signal = false
+					break
+				}
+			}
+		}
+		// Use a deferred call to ensure that we report that the test is
+		// complete even if a cleanup function calls t.FailNow. See issue 41355.
+		didPanic := false
+		defer func() {
+			if didPanic {
+				return
+			}
+			if err != nil {
+				panic(err)
+			}
+			// Only report that the test is complete if it doesn't panic,
+			// as otherwise the test binary can exit before the panic is
+			// reported to the user. See issue 41479.
+			t.signal <- signal
+		}()
+
+		doPanic := func(err interface{}) {
+			t.Fail()
+			if r := t.runCleanup(recoverAndReturnPanic); r != nil {
+				t.Logf("cleanup panicked with %v", r)
+			}
+			// Flush the output log up to the root before dying.
+			for root := &t.common; root.parent != nil; root = root.parent {
+				root.mu.Lock()
+				root.duration += time.Since(root.start)
+				d := root.duration
+				root.mu.Unlock()
+				root.flushToParent(root.name, "--- FAIL: %s (%s)\n", root.name, fmtDuration(d))
+				if r := root.parent.runCleanup(recoverAndReturnPanic); r != nil {
+					fmt.Fprintf(root.parent.w, "cleanup panicked with %v", r)
+				}
+			}
+			didPanic = true
+			panic(err)
+		}
+		if err != nil {
+			doPanic(err)
+		}
+
+		t.duration += time.Since(t.start)
+
+		if len(t.sub) > 0 {
+			// Run parallel subtests.
+			// Decrease the running count for this test.
+			t.context.release()
+			// Release the parallel subtests.
+			close(t.barrier)
+			// Wait for subtests to complete.
+			for _, sub := range t.sub {
+				<-sub.signal
+			}
+			cleanupStart := time.Now()
+			err := t.runCleanup(recoverAndReturnPanic)
+			t.duration += time.Since(cleanupStart)
+			if err != nil {
+				doPanic(err)
+			}
+			if !t.isParallel {
+				// Reacquire the count for sequential tests. See comment in Run.
+				t.context.waitParallel()
+			}
+		} else if t.isParallel {
+			// Only release the count for this test if it was run as a parallel
+			// test. See comment in Run method.
+			t.context.release()
+		}
+		t.report() // Report after all subtests have finished.
+
+		// Do not lock t.done to allow race detector to detect race in case
+		// the user does not appropriately synchronizes a goroutine.
+		t.done = true
+		if t.parent != nil && atomic.LoadInt32(&t.hasSub) == 0 {
+			t.setRan()
+		}
+	}()
+	defer func() {
+		if len(t.sub) == 0 {
+			t.runCleanup(normalPanic)
+		}
+	}()
+
+	t.start = time.Now()
+	t.raceErrors = -race.Errors()
+	fn(t)
+
+	// code beyond here will not be executed when FailNow is invoked
+	t.finished = true
+}
+
+// Run runs f as a subtest of t called name. It runs f in a separate goroutine
+// and blocks until f returns or calls t.Parallel to become a parallel test.
+// Run reports whether f succeeded (or at least did not fail before calling t.Parallel).
+//
+// Run may be called simultaneously from multiple goroutines, but all such calls
+// must return before the outer test function for t returns.
+func (t *T) Run(name string, f func(t *T)) bool {
+	atomic.StoreInt32(&t.hasSub, 1)
+	testName, ok, _ := t.context.match.fullName(&t.common, name)
+	if !ok || shouldFailFast() {
+		return true
+	}
+	// Record the stack trace at the point of this call so that if the subtest
+	// function - which runs in a separate stack - is marked as a helper, we can
+	// continue walking the stack into the parent test.
+	var pc [maxStackLen]uintptr
+	n := runtime.Callers(2, pc[:])
+	t = &T{
+		common: common{
+			barrier: make(chan bool),
+			signal:  make(chan bool),
+			name:    testName,
+			parent:  &t.common,
+			level:   t.level + 1,
+			creator: pc[:n],
+			chatty:  t.chatty,
+		},
+		context: t.context,
+	}
+	t.w = indenter{&t.common}
+
+	if t.chatty != nil {
+		t.chatty.Updatef(t.name, "=== RUN   %s\n", t.name)
+	}
+	// Instead of reducing the running count of this test before calling the
+	// tRunner and increasing it afterwards, we rely on tRunner keeping the
+	// count correct. This ensures that a sequence of sequential tests runs
+	// without being preempted, even when their parent is a parallel test. This
+	// may especially reduce surprises if *parallel == 1.
+	go tRunner(t, f)
+	if !<-t.signal {
+		// At this point, it is likely that FailNow was called on one of the
+		// parent tests by one of the subtests. Continue aborting up the chain.
+		runtime.Goexit()
+	}
+	return !t.failed
+}
+
+// Deadline reports the time at which the test binary will have
+// exceeded the timeout specified by the -timeout flag.
+//
+// The ok result is false if the -timeout flag indicates “no timeout” (0).
+func (t *T) Deadline() (deadline time.Time, ok bool) {
+	deadline = t.context.deadline
+	return deadline, !deadline.IsZero()
+}
+
+// testContext holds all fields that are common to all tests. This includes
+// synchronization primitives to run at most *parallel tests.
+type testContext struct {
+	match    *matcher
+	deadline time.Time
+
+	mu sync.Mutex
+
+	// Channel used to signal tests that are ready to be run in parallel.
+	startParallel chan bool
+
+	// running is the number of tests currently running in parallel.
+	// This does not include tests that are waiting for subtests to complete.
+	running int
+
+	// numWaiting is the number tests waiting to be run in parallel.
+	numWaiting int
+
+	// maxParallel is a copy of the parallel flag.
+	maxParallel int
+}
+
+func newTestContext(maxParallel int, m *matcher) *testContext {
+	return &testContext{
+		match:         m,
+		startParallel: make(chan bool),
+		maxParallel:   maxParallel,
+		running:       1, // Set the count to 1 for the main (sequential) test.
+	}
+}
+
+func (c *testContext) waitParallel() {
+	c.mu.Lock()
+	if c.running < c.maxParallel {
+		c.running++
+		c.mu.Unlock()
+		return
+	}
+	c.numWaiting++
+	c.mu.Unlock()
+	<-c.startParallel
+}
+
+func (c *testContext) release() {
+	c.mu.Lock()
+	if c.numWaiting == 0 {
+		c.running--
+		c.mu.Unlock()
+		return
+	}
+	c.numWaiting--
+	c.mu.Unlock()
+	c.startParallel <- true // Pick a waiting test to be run.
+}
+
+// No one should be using func Main anymore.
+// See the doc comment on func Main and use MainStart instead.
+var errMain = errors.New("testing: unexpected use of func Main")
+
+type matchStringOnly func(pat, str string) (bool, error)
+
+func (f matchStringOnly) MatchString(pat, str string) (bool, error)   { return f(pat, str) }
+func (f matchStringOnly) StartCPUProfile(w io.Writer) error           { return errMain }
+func (f matchStringOnly) StopCPUProfile()                             {}
+func (f matchStringOnly) WriteProfileTo(string, io.Writer, int) error { return errMain }
+func (f matchStringOnly) ImportPath() string                          { return "" }
+func (f matchStringOnly) StartTestLog(io.Writer)                      {}
+func (f matchStringOnly) StopTestLog() error                          { return errMain }
+func (f matchStringOnly) SetPanicOnExit0(bool)                        {}
+
+// Main is an internal function, part of the implementation of the "go test" command.
+// It was exported because it is cross-package and predates "internal" packages.
+// It is no longer used by "go test" but preserved, as much as possible, for other
+// systems that simulate "go test" using Main, but Main sometimes cannot be updated as
+// new functionality is added to the testing package.
+// Systems simulating "go test" should be updated to use MainStart.
+func Main(matchString func(pat, str string) (bool, error), tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample) {
+	os.Exit(MainStart(matchStringOnly(matchString), tests, benchmarks, examples).Run())
+}
+
+// M is a type passed to a TestMain function to run the actual tests.
+type M struct {
+	deps       testDeps
+	tests      []InternalTest
+	benchmarks []InternalBenchmark
+	examples   []InternalExample
+
+	timer     *time.Timer
+	afterOnce sync.Once
+
+	numRun int
+
+	// value to pass to os.Exit, the outer test func main
+	// harness calls os.Exit with this code. See #34129.
+	exitCode int
+}
+
+// testDeps is an internal interface of functionality that is
+// passed into this package by a test's generated main package.
+// The canonical implementation of this interface is
+// testing/internal/testdeps's TestDeps.
+type testDeps interface {
+	ImportPath() string
+	MatchString(pat, str string) (bool, error)
+	SetPanicOnExit0(bool)
+	StartCPUProfile(io.Writer) error
+	StopCPUProfile()
+	StartTestLog(io.Writer)
+	StopTestLog() error
+	WriteProfileTo(string, io.Writer, int) error
+}
+
+// MainStart is meant for use by tests generated by 'go test'.
+// It is not meant to be called directly and is not subject to the Go 1 compatibility document.
+// It may change signature from release to release.
+func MainStart(deps testDeps, tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample) *M {
+	Init()
+	return &M{
+		deps:       deps,
+		tests:      tests,
+		benchmarks: benchmarks,
+		examples:   examples,
+	}
+}
+
+// Run runs the tests. It returns an exit code to pass to os.Exit.
+func (m *M) Run() (code int) {
+	defer func() {
+		code = m.exitCode
+	}()
+
+	// Count the number of calls to m.Run.
+	// We only ever expected 1, but we didn't enforce that,
+	// and now there are tests in the wild that call m.Run multiple times.
+	// Sigh. golang.org/issue/23129.
+	m.numRun++
+
+	// TestMain may have already called flag.Parse.
+	if !flag.Parsed() {
+		flag.Parse()
+	}
+
+	if *parallel < 1 {
+		fmt.Fprintln(os.Stderr, "testing: -parallel can only be given a positive integer")
+		flag.Usage()
+		m.exitCode = 2
+		return
+	}
+
+	if len(*matchList) != 0 {
+		listTests(m.deps.MatchString, m.tests, m.benchmarks, m.examples)
+		m.exitCode = 0
+		return
+	}
+
+	parseCpuList()
+
+	m.before()
+	defer m.after()
+	deadline := m.startAlarm()
+	haveExamples = len(m.examples) > 0
+	testRan, testOk := runTests(m.deps.MatchString, m.tests, deadline)
+	exampleRan, exampleOk := runExamples(m.deps.MatchString, m.examples)
+	m.stopAlarm()
+	if !testRan && !exampleRan && *matchBenchmarks == "" {
+		fmt.Fprintln(os.Stderr, "testing: warning: no tests to run")
+	}
+	if !testOk || !exampleOk || !runBenchmarks(m.deps.ImportPath(), m.deps.MatchString, m.benchmarks) || race.Errors() > 0 {
+		fmt.Println("FAIL")
+		m.exitCode = 1
+		return
+	}
+
+	fmt.Println("PASS")
+	m.exitCode = 0
+	return
+}
+
+func (t *T) report() {
+	if t.parent == nil {
+		return
+	}
+	dstr := fmtDuration(t.duration)
+	format := "--- %s: %s (%s)\n"
+	if t.Failed() {
+		t.flushToParent(t.name, format, "FAIL", t.name, dstr)
+	} else if t.chatty != nil {
+		if t.Skipped() {
+			t.flushToParent(t.name, format, "SKIP", t.name, dstr)
+		} else {
+			t.flushToParent(t.name, format, "PASS", t.name, dstr)
+		}
+	}
+}
+
+func listTests(matchString func(pat, str string) (bool, error), tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample) {
+	if _, err := matchString(*matchList, "non-empty"); err != nil {
+		fmt.Fprintf(os.Stderr, "testing: invalid regexp in -test.list (%q): %s\n", *matchList, err)
+		os.Exit(1)
+	}
+
+	for _, test := range tests {
+		if ok, _ := matchString(*matchList, test.Name); ok {
+			fmt.Println(test.Name)
+		}
+	}
+	for _, bench := range benchmarks {
+		if ok, _ := matchString(*matchList, bench.Name); ok {
+			fmt.Println(bench.Name)
+		}
+	}
+	for _, example := range examples {
+		if ok, _ := matchString(*matchList, example.Name); ok {
+			fmt.Println(example.Name)
+		}
+	}
+}
+
+// RunTests is an internal function but exported because it is cross-package;
+// it is part of the implementation of the "go test" command.
+func RunTests(matchString func(pat, str string) (bool, error), tests []InternalTest) (ok bool) {
+	var deadline time.Time
+	if *timeout > 0 {
+		deadline = time.Now().Add(*timeout)
+	}
+	ran, ok := runTests(matchString, tests, deadline)
+	if !ran && !haveExamples {
+		fmt.Fprintln(os.Stderr, "testing: warning: no tests to run")
+	}
+	return ok
+}
+
+func runTests(matchString func(pat, str string) (bool, error), tests []InternalTest, deadline time.Time) (ran, ok bool) {
+	ok = true
+	for _, procs := range cpuList {
+		runtime.GOMAXPROCS(procs)
+		for i := uint(0); i < *count; i++ {
+			if shouldFailFast() {
+				break
+			}
+			ctx := newTestContext(*parallel, newMatcher(matchString, *match, "-test.run"))
+			ctx.deadline = deadline
+			t := &T{
+				common: common{
+					signal:  make(chan bool),
+					barrier: make(chan bool),
+					w:       os.Stdout,
+				},
+				context: ctx,
+			}
+			if Verbose() {
+				t.chatty = newChattyPrinter(t.w)
+			}
+			tRunner(t, func(t *T) {
+				for _, test := range tests {
+					t.Run(test.Name, test.F)
+				}
+				// Run catching the signal rather than the tRunner as a separate
+				// goroutine to avoid adding a goroutine during the sequential
+				// phase as this pollutes the stacktrace output when aborting.
+				go func() { <-t.signal }()
+			})
+			ok = ok && !t.Failed()
+			ran = ran || t.ran
+		}
+	}
+	return ran, ok
+}
+
+// before runs before all testing.
+func (m *M) before() {
+	if *memProfileRate > 0 {
+		runtime.MemProfileRate = *memProfileRate
+	}
+	if *cpuProfile != "" {
+		f, err := os.Create(toOutputDir(*cpuProfile))
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "testing: %s\n", err)
+			return
+		}
+		if err := m.deps.StartCPUProfile(f); err != nil {
+			fmt.Fprintf(os.Stderr, "testing: can't start cpu profile: %s\n", err)
+			f.Close()
+			return
+		}
+		// Could save f so after can call f.Close; not worth the effort.
+	}
+	if *traceFile != "" {
+		f, err := os.Create(toOutputDir(*traceFile))
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "testing: %s\n", err)
+			return
+		}
+		if err := trace.Start(f); err != nil {
+			fmt.Fprintf(os.Stderr, "testing: can't start tracing: %s\n", err)
+			f.Close()
+			return
+		}
+		// Could save f so after can call f.Close; not worth the effort.
+	}
+	if *blockProfile != "" && *blockProfileRate >= 0 {
+		runtime.SetBlockProfileRate(*blockProfileRate)
+	}
+	if *mutexProfile != "" && *mutexProfileFraction >= 0 {
+		runtime.SetMutexProfileFraction(*mutexProfileFraction)
+	}
+	if *coverProfile != "" && cover.Mode == "" {
+		fmt.Fprintf(os.Stderr, "testing: cannot use -test.coverprofile because test binary was not built with coverage enabled\n")
+		os.Exit(2)
+	}
+	if *testlog != "" {
+		// Note: Not using toOutputDir.
+		// This file is for use by cmd/go, not users.
+		var f *os.File
+		var err error
+		if m.numRun == 1 {
+			f, err = os.Create(*testlog)
+		} else {
+			f, err = os.OpenFile(*testlog, os.O_WRONLY, 0)
+			if err == nil {
+				f.Seek(0, io.SeekEnd)
+			}
+		}
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "testing: %s\n", err)
+			os.Exit(2)
+		}
+		m.deps.StartTestLog(f)
+		testlogFile = f
+	}
+	if *panicOnExit0 {
+		m.deps.SetPanicOnExit0(true)
+	}
+}
+
+// after runs after all testing.
+func (m *M) after() {
+	m.afterOnce.Do(func() {
+		m.writeProfiles()
+	})
+
+	// Restore PanicOnExit0 after every run, because we set it to true before
+	// every run. Otherwise, if m.Run is called multiple times the behavior of
+	// os.Exit(0) will not be restored after the second run.
+	if *panicOnExit0 {
+		m.deps.SetPanicOnExit0(false)
+	}
+}
+
+func (m *M) writeProfiles() {
+	if *testlog != "" {
+		if err := m.deps.StopTestLog(); err != nil {
+			fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *testlog, err)
+			os.Exit(2)
+		}
+		if err := testlogFile.Close(); err != nil {
+			fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *testlog, err)
+			os.Exit(2)
+		}
+	}
+	if *cpuProfile != "" {
+		m.deps.StopCPUProfile() // flushes profile to disk
+	}
+	if *traceFile != "" {
+		trace.Stop() // flushes trace to disk
+	}
+	if *memProfile != "" {
+		f, err := os.Create(toOutputDir(*memProfile))
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "testing: %s\n", err)
+			os.Exit(2)
+		}
+		runtime.GC() // materialize all statistics
+		if err = m.deps.WriteProfileTo("allocs", f, 0); err != nil {
+			fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *memProfile, err)
+			os.Exit(2)
+		}
+		f.Close()
+	}
+	if *blockProfile != "" && *blockProfileRate >= 0 {
+		f, err := os.Create(toOutputDir(*blockProfile))
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "testing: %s\n", err)
+			os.Exit(2)
+		}
+		if err = m.deps.WriteProfileTo("block", f, 0); err != nil {
+			fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *blockProfile, err)
+			os.Exit(2)
+		}
+		f.Close()
+	}
+	if *mutexProfile != "" && *mutexProfileFraction >= 0 {
+		f, err := os.Create(toOutputDir(*mutexProfile))
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "testing: %s\n", err)
+			os.Exit(2)
+		}
+		if err = m.deps.WriteProfileTo("mutex", f, 0); err != nil {
+			fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *mutexProfile, err)
+			os.Exit(2)
+		}
+		f.Close()
+	}
+	if cover.Mode != "" {
+		coverReport()
+	}
+}
+
+// toOutputDir returns the file name relocated, if required, to outputDir.
+// Simple implementation to avoid pulling in path/filepath.
+func toOutputDir(path string) string {
+	if *outputDir == "" || path == "" {
+		return path
+	}
+	// On Windows, it's clumsy, but we can be almost always correct
+	// by just looking for a drive letter and a colon.
+	// Absolute paths always have a drive letter (ignoring UNC).
+	// Problem: if path == "C:A" and outputdir == "C:\Go" it's unclear
+	// what to do, but even then path/filepath doesn't help.
+	// TODO: Worth doing better? Probably not, because we're here only
+	// under the management of go test.
+	if runtime.GOOS == "windows" && len(path) >= 2 {
+		letter, colon := path[0], path[1]
+		if ('a' <= letter && letter <= 'z' || 'A' <= letter && letter <= 'Z') && colon == ':' {
+			// If path starts with a drive letter we're stuck with it regardless.
+			return path
+		}
+	}
+	if os.IsPathSeparator(path[0]) {
+		return path
+	}
+	return fmt.Sprintf("%s%c%s", *outputDir, os.PathSeparator, path)
+}
+
+// startAlarm starts an alarm if requested.
+func (m *M) startAlarm() time.Time {
+	if *timeout <= 0 {
+		return time.Time{}
+	}
+
+	deadline := time.Now().Add(*timeout)
+	m.timer = time.AfterFunc(*timeout, func() {
+		m.after()
+		debug.SetTraceback("all")
+		panic(fmt.Sprintf("test timed out after %v", *timeout))
+	})
+	return deadline
+}
+
+// stopAlarm turns off the alarm.
+func (m *M) stopAlarm() {
+	if *timeout > 0 {
+		m.timer.Stop()
+	}
+}
+
+func parseCpuList() {
+	for _, val := range strings.Split(*cpuListStr, ",") {
+		val = strings.TrimSpace(val)
+		if val == "" {
+			continue
+		}
+		cpu, err := strconv.Atoi(val)
+		if err != nil || cpu <= 0 {
+			fmt.Fprintf(os.Stderr, "testing: invalid value %q for -test.cpu\n", val)
+			os.Exit(1)
+		}
+		cpuList = append(cpuList, cpu)
+	}
+	if cpuList == nil {
+		cpuList = append(cpuList, runtime.GOMAXPROCS(-1))
+	}
+}
+
+func shouldFailFast() bool {
+	return *failFast && atomic.LoadUint32(&numFailed) > 0
+}
diff --git a/src/testing/testing_test.go b/src/testing/testing_test.go
new file mode 100644
index 0000000..0f09698
--- /dev/null
+++ b/src/testing/testing_test.go
@@ -0,0 +1,111 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testing_test
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// This is exactly what a test would do without a TestMain.
+// It's here only so that there is at least one package in the
+// standard library with a TestMain, so that code is executed.
+
+func TestMain(m *testing.M) {
+	os.Exit(m.Run())
+}
+
+func TestTempDirInCleanup(t *testing.T) {
+	var dir string
+
+	t.Run("test", func(t *testing.T) {
+		t.Cleanup(func() {
+			dir = t.TempDir()
+		})
+		_ = t.TempDir()
+	})
+
+	fi, err := os.Stat(dir)
+	if fi != nil {
+		t.Fatalf("Directory %q from user Cleanup still exists", dir)
+	}
+	if !os.IsNotExist(err) {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+}
+
+func TestTempDirInBenchmark(t *testing.T) {
+	testing.Benchmark(func(b *testing.B) {
+		if !b.Run("test", func(b *testing.B) {
+			// Add a loop so that the test won't fail. See issue 38677.
+			for i := 0; i < b.N; i++ {
+				_ = b.TempDir()
+			}
+		}) {
+			t.Fatal("Sub test failure in a benchmark")
+		}
+	})
+}
+
+func TestTempDir(t *testing.T) {
+	testTempDir(t)
+	t.Run("InSubtest", testTempDir)
+	t.Run("test/subtest", testTempDir)
+	t.Run("test\\subtest", testTempDir)
+	t.Run("test:subtest", testTempDir)
+	t.Run("test/..", testTempDir)
+	t.Run("../test", testTempDir)
+}
+
+func testTempDir(t *testing.T) {
+	dirCh := make(chan string, 1)
+	t.Cleanup(func() {
+		// Verify directory has been removed.
+		select {
+		case dir := <-dirCh:
+			fi, err := os.Stat(dir)
+			if os.IsNotExist(err) {
+				// All good
+				return
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+			t.Errorf("directory %q stil exists: %v, isDir=%v", dir, fi, fi.IsDir())
+		default:
+			if !t.Failed() {
+				t.Fatal("never received dir channel")
+			}
+		}
+	})
+
+	dir := t.TempDir()
+	if dir == "" {
+		t.Fatal("expected dir")
+	}
+	dir2 := t.TempDir()
+	if dir == dir2 {
+		t.Fatal("subsequent calls to TempDir returned the same directory")
+	}
+	if filepath.Dir(dir) != filepath.Dir(dir2) {
+		t.Fatalf("calls to TempDir do not share a parent; got %q, %q", dir, dir2)
+	}
+	dirCh <- dir
+	fi, err := os.Stat(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !fi.IsDir() {
+		t.Errorf("dir %q is not a dir", dir)
+	}
+	files, err := os.ReadDir(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(files) > 0 {
+		t.Errorf("unexpected %d files in TempDir: %v", len(files), files)
+	}
+}