10 files changed, 720 insertions, 0 deletions
diff --git a/src/internal/testenv/exec.go b/src/internal/testenv/exec.go
new file mode 100644
index 0000000..77de59c
--- /dev/null
+++ b/src/internal/testenv/exec.go
@@ -0,0 +1,175 @@
+// 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 testenv
+
+import (
+	"context"
+	"os"
+	"os/exec"
+	"runtime"
+	"strconv"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+)
+
+// HasExec reports whether the current system can start new processes
+// using os.StartProcess or (more commonly) exec.Command.
+func HasExec() bool {
+	switch runtime.GOOS {
+	case "js", "ios":
+		return false
+	}
+	return true
+}
+
+// MustHaveExec checks that the current system can start new processes
+// using os.StartProcess or (more commonly) exec.Command.
+// If not, MustHaveExec calls t.Skip with an explanation.
+func MustHaveExec(t testing.TB) {
+	if !HasExec() {
+		t.Skipf("skipping test: cannot exec subprocess on %s/%s", runtime.GOOS, runtime.GOARCH)
+	}
+}
+
+var execPaths sync.Map // path -> error
+
+// MustHaveExecPath checks that the current system can start the named executable
+// using os.StartProcess or (more commonly) exec.Command.
+// If not, MustHaveExecPath calls t.Skip with an explanation.
+func MustHaveExecPath(t testing.TB, path string) {
+	MustHaveExec(t)
+
+	err, found := execPaths.Load(path)
+	if !found {
+		_, err = exec.LookPath(path)
+		err, _ = execPaths.LoadOrStore(path, err)
+	}
+	if err != nil {
+		t.Skipf("skipping test: %s: %s", path, err)
+	}
+}
+
+// CleanCmdEnv will fill cmd.Env with the environment, excluding certain
+// variables that could modify the behavior of the Go tools such as
+// GODEBUG and GOTRACEBACK.
+func CleanCmdEnv(cmd *exec.Cmd) *exec.Cmd {
+	if cmd.Env != nil {
+		panic("environment already set")
+	}
+	for _, env := range os.Environ() {
+		// Exclude GODEBUG from the environment to prevent its output
+		// from breaking tests that are trying to parse other command output.
+		if strings.HasPrefix(env, "GODEBUG=") {
+			continue
+		}
+		// Exclude GOTRACEBACK for the same reason.
+		if strings.HasPrefix(env, "GOTRACEBACK=") {
+			continue
+		}
+		cmd.Env = append(cmd.Env, env)
+	}
+	return cmd
+}
+
+// CommandContext is like exec.CommandContext, but:
+//   - skips t if the platform does not support os/exec,
+//   - sends SIGQUIT (if supported by the platform) instead of SIGKILL
+//     in its Cancel function
+//   - if the test has a deadline, adds a Context timeout and WaitDelay
+//     for an arbitrary grace period before the test's deadline expires,
+//   - fails the test if the command does not complete before the test's deadline, and
+//   - sets a Cleanup function that verifies that the test did not leak a subprocess.
+func CommandContext(t testing.TB, ctx context.Context, name string, args ...string) *exec.Cmd {
+	t.Helper()
+	MustHaveExec(t)
+
+	var (
+		cancelCtx   context.CancelFunc
+		gracePeriod time.Duration // unlimited unless the test has a deadline (to allow for interactive debugging)
+	)
+
+	if t, ok := t.(interface {
+		testing.TB
+		Deadline() (time.Time, bool)
+	}); ok {
+		if td, ok := t.Deadline(); ok {
+			// Start with a minimum grace period, just long enough to consume the
+			// output of a reasonable program after it terminates.
+			gracePeriod = 100 * time.Millisecond
+			if s := os.Getenv("GO_TEST_TIMEOUT_SCALE"); s != "" {
+				scale, err := strconv.Atoi(s)
+				if err != nil {
+					t.Fatalf("invalid GO_TEST_TIMEOUT_SCALE: %v", err)
+				}
+				gracePeriod *= time.Duration(scale)
+			}
+
+			// If time allows, increase the termination grace period to 5% of the
+			// test's remaining time.
+			testTimeout := time.Until(td)
+			if gp := testTimeout / 20; gp > gracePeriod {
+				gracePeriod = gp
+			}
+
+			// When we run commands that execute subprocesses, we want to reserve two
+			// grace periods to clean up: one for the delay between the first
+			// termination signal being sent (via the Cancel callback when the Context
+			// expires) and the process being forcibly terminated (via the WaitDelay
+			// field), and a second one for the delay becween the process being
+			// terminated and and the test logging its output for debugging.
+			//
+			// (We want to ensure that the test process itself has enough time to
+			// log the output before it is also terminated.)
+			cmdTimeout := testTimeout - 2*gracePeriod
+
+			if cd, ok := ctx.Deadline(); !ok || time.Until(cd) > cmdTimeout {
+				// Either ctx doesn't have a deadline, or its deadline would expire
+				// after (or too close before) the test has already timed out.
+				// Add a shorter timeout so that the test will produce useful output.
+				ctx, cancelCtx = context.WithTimeout(ctx, cmdTimeout)
+			}
+		}
+	}
+
+	cmd := exec.CommandContext(ctx, name, args...)
+	cmd.Cancel = func() error {
+		if cancelCtx != nil && ctx.Err() == context.DeadlineExceeded {
+			// The command timed out due to running too close to the test's deadline.
+			// There is no way the test did that intentionally — it's too close to the
+			// wire! — so mark it as a test failure. That way, if the test expects the
+			// command to fail for some other reason, it doesn't have to distinguish
+			// between that reason and a timeout.
+			t.Errorf("test timed out while running command: %v", cmd)
+		} else {
+			// The command is being terminated due to ctx being canceled, but
+			// apparently not due to an explicit test deadline that we added.
+			// Log that information in case it is useful for diagnosing a failure,
+			// but don't actually fail the test because of it.
+			t.Logf("%v: terminating command: %v", ctx.Err(), cmd)
+		}
+		return cmd.Process.Signal(Sigquit)
+	}
+	cmd.WaitDelay = gracePeriod
+
+	t.Cleanup(func() {
+		if cancelCtx != nil {
+			cancelCtx()
+		}
+		if cmd.Process != nil && cmd.ProcessState == nil {
+			t.Errorf("command was started, but test did not wait for it to complete: %v", cmd)
+		}
+	})
+
+	return cmd
+}
+
+// Command is like exec.Command, but applies the same changes as
+// testenv.CommandContext (with a default Context).
+func Command(t testing.TB, name string, args ...string) *exec.Cmd {
+	t.Helper()
+	return CommandContext(t, context.Background(), name, args...)
+}
diff --git a/src/internal/testenv/noopt.go b/src/internal/testenv/noopt.go
new file mode 100644
index 0000000..ae2a3d0
--- /dev/null
+++ b/src/internal/testenv/noopt.go
@@ -0,0 +1,12 @@
+// Copyright 2022 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.
+
+//go:build noopt
+
+package testenv
+
+// OptimizationOff reports whether optimization is disabled.
+func OptimizationOff() bool {
+	return true
+}
diff --git a/src/internal/testenv/opt.go b/src/internal/testenv/opt.go
new file mode 100644
index 0000000..1bb96f7
--- /dev/null
+++ b/src/internal/testenv/opt.go
@@ -0,0 +1,12 @@
+// Copyright 2022 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.
+
+//go:build !noopt
+
+package testenv
+
+// OptimizationOff reports whether optimization is disabled.
+func OptimizationOff() bool {
+	return false
+}
diff --git a/src/internal/testenv/testenv.go b/src/internal/testenv/testenv.go
new file mode 100644
index 0000000..6a28b25
--- /dev/null
+++ b/src/internal/testenv/testenv.go
@@ -0,0 +1,364 @@
+// 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 testenv provides information about what functionality
+// is available in different testing environments run by the Go team.
+//
+// It is an internal package because these details are specific
+// to the Go team's test setup (on build.golang.org) and not
+// fundamental to tests in general.
+package testenv
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"internal/cfg"
+	"internal/goroot"
+	"internal/platform"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+	"sync"
+	"testing"
+)
+
+// Builder reports the name of the builder running this test
+// (for example, "linux-amd64" or "windows-386-gce").
+// If the test is not running on the build infrastructure,
+// Builder returns the empty string.
+func Builder() string {
+	return os.Getenv("GO_BUILDER_NAME")
+}
+
+// HasGoBuild reports whether the current system can build programs with “go build”
+// and then run them with os.StartProcess or exec.Command.
+func HasGoBuild() bool {
+	if os.Getenv("GO_GCFLAGS") != "" {
+		// It's too much work to require every caller of the go command
+		// to pass along "-gcflags="+os.Getenv("GO_GCFLAGS").
+		// For now, if $GO_GCFLAGS is set, report that we simply can't
+		// run go build.
+		return false
+	}
+	switch runtime.GOOS {
+	case "android", "js", "ios":
+		return false
+	}
+	return true
+}
+
+// MustHaveGoBuild checks that the current system can build programs with “go build”
+// and then run them with os.StartProcess or exec.Command.
+// If not, MustHaveGoBuild calls t.Skip with an explanation.
+func MustHaveGoBuild(t testing.TB) {
+	if os.Getenv("GO_GCFLAGS") != "" {
+		t.Skipf("skipping test: 'go build' not compatible with setting $GO_GCFLAGS")
+	}
+	if !HasGoBuild() {
+		t.Skipf("skipping test: 'go build' not available on %s/%s", runtime.GOOS, runtime.GOARCH)
+	}
+}
+
+// HasGoRun reports whether the current system can run programs with “go run.”
+func HasGoRun() bool {
+	// For now, having go run and having go build are the same.
+	return HasGoBuild()
+}
+
+// MustHaveGoRun checks that the current system can run programs with “go run.”
+// If not, MustHaveGoRun calls t.Skip with an explanation.
+func MustHaveGoRun(t testing.TB) {
+	if !HasGoRun() {
+		t.Skipf("skipping test: 'go run' not available on %s/%s", runtime.GOOS, runtime.GOARCH)
+	}
+}
+
+// GoToolPath reports the path to the Go tool.
+// It is a convenience wrapper around GoTool.
+// If the tool is unavailable GoToolPath calls t.Skip.
+// If the tool should be available and isn't, GoToolPath calls t.Fatal.
+func GoToolPath(t testing.TB) string {
+	MustHaveGoBuild(t)
+	path, err := GoTool()
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Add all environment variables that affect the Go command to test metadata.
+	// Cached test results will be invalidate when these variables change.
+	// See golang.org/issue/32285.
+	for _, envVar := range strings.Fields(cfg.KnownEnv) {
+		os.Getenv(envVar)
+	}
+	return path
+}
+
+var (
+	gorootOnce sync.Once
+	gorootPath string
+	gorootErr  error
+)
+
+func findGOROOT() (string, error) {
+	gorootOnce.Do(func() {
+		gorootPath = runtime.GOROOT()
+		if gorootPath != "" {
+			// If runtime.GOROOT() is non-empty, assume that it is valid.
+			//
+			// (It might not be: for example, the user may have explicitly set GOROOT
+			// to the wrong directory, or explicitly set GOROOT_FINAL but not GOROOT
+			// and hasn't moved the tree to GOROOT_FINAL yet. But those cases are
+			// rare, and if that happens the user can fix what they broke.)
+			return
+		}
+
+		// runtime.GOROOT doesn't know where GOROOT is (perhaps because the test
+		// binary was built with -trimpath, or perhaps because GOROOT_FINAL was set
+		// without GOROOT and the tree hasn't been moved there yet).
+		//
+		// Since this is internal/testenv, we can cheat and assume that the caller
+		// is a test of some package in a subdirectory of GOROOT/src. ('go test'
+		// runs the test in the directory containing the packaged under test.) That
+		// means that if we start walking up the tree, we should eventually find
+		// GOROOT/src/go.mod, and we can report the parent directory of that.
+
+		cwd, err := os.Getwd()
+		if err != nil {
+			gorootErr = fmt.Errorf("finding GOROOT: %w", err)
+			return
+		}
+
+		dir := cwd
+		for {
+			parent := filepath.Dir(dir)
+			if parent == dir {
+				// dir is either "." or only a volume name.
+				gorootErr = fmt.Errorf("failed to locate GOROOT/src in any parent directory")
+				return
+			}
+
+			if base := filepath.Base(dir); base != "src" {
+				dir = parent
+				continue // dir cannot be GOROOT/src if it doesn't end in "src".
+			}
+
+			b, err := os.ReadFile(filepath.Join(dir, "go.mod"))
+			if err != nil {
+				if os.IsNotExist(err) {
+					dir = parent
+					continue
+				}
+				gorootErr = fmt.Errorf("finding GOROOT: %w", err)
+				return
+			}
+			goMod := string(b)
+
+			for goMod != "" {
+				var line string
+				line, goMod, _ = strings.Cut(goMod, "\n")
+				fields := strings.Fields(line)
+				if len(fields) >= 2 && fields[0] == "module" && fields[1] == "std" {
+					// Found "module std", which is the module declaration in GOROOT/src!
+					gorootPath = parent
+					return
+				}
+			}
+		}
+	})
+
+	return gorootPath, gorootErr
+}
+
+// GOROOT reports the path to the directory containing the root of the Go
+// project source tree. This is normally equivalent to runtime.GOROOT, but
+// works even if the test binary was built with -trimpath.
+//
+// If GOROOT cannot be found, GOROOT skips t if t is non-nil,
+// or panics otherwise.
+func GOROOT(t testing.TB) string {
+	path, err := findGOROOT()
+	if err != nil {
+		if t == nil {
+			panic(err)
+		}
+		t.Helper()
+		t.Skip(err)
+	}
+	return path
+}
+
+// GoTool reports the path to the Go tool.
+func GoTool() (string, error) {
+	if !HasGoBuild() {
+		return "", errors.New("platform cannot run go tool")
+	}
+	var exeSuffix string
+	if runtime.GOOS == "windows" {
+		exeSuffix = ".exe"
+	}
+	goroot, err := findGOROOT()
+	if err != nil {
+		return "", fmt.Errorf("cannot find go tool: %w", err)
+	}
+	path := filepath.Join(goroot, "bin", "go"+exeSuffix)
+	if _, err := os.Stat(path); err == nil {
+		return path, nil
+	}
+	goBin, err := exec.LookPath("go" + exeSuffix)
+	if err != nil {
+		return "", errors.New("cannot find go tool: " + err.Error())
+	}
+	return goBin, nil
+}
+
+// HasSrc reports whether the entire source tree is available under GOROOT.
+func HasSrc() bool {
+	switch runtime.GOOS {
+	case "ios":
+		return false
+	}
+	return true
+}
+
+// HasExternalNetwork reports whether the current system can use
+// external (non-localhost) networks.
+func HasExternalNetwork() bool {
+	return !testing.Short() && runtime.GOOS != "js"
+}
+
+// MustHaveExternalNetwork checks that the current system can use
+// external (non-localhost) networks.
+// If not, MustHaveExternalNetwork calls t.Skip with an explanation.
+func MustHaveExternalNetwork(t testing.TB) {
+	if runtime.GOOS == "js" {
+		t.Skipf("skipping test: no external network on %s", runtime.GOOS)
+	}
+	if testing.Short() {
+		t.Skipf("skipping test: no external network in -short mode")
+	}
+}
+
+var haveCGO bool
+
+// HasCGO reports whether the current system can use cgo.
+func HasCGO() bool {
+	return haveCGO
+}
+
+// MustHaveCGO calls t.Skip if cgo is not available.
+func MustHaveCGO(t testing.TB) {
+	if !haveCGO {
+		t.Skipf("skipping test: no cgo")
+	}
+}
+
+// CanInternalLink reports whether the current system can link programs with
+// internal linking.
+func CanInternalLink() bool {
+	return !platform.MustLinkExternal(runtime.GOOS, runtime.GOARCH)
+}
+
+// MustInternalLink checks that the current system can link programs with internal
+// linking.
+// If not, MustInternalLink calls t.Skip with an explanation.
+func MustInternalLink(t testing.TB) {
+	if !CanInternalLink() {
+		t.Skipf("skipping test: internal linking on %s/%s is not supported", runtime.GOOS, runtime.GOARCH)
+	}
+}
+
+// HasSymlink reports whether the current system can use os.Symlink.
+func HasSymlink() bool {
+	ok, _ := hasSymlink()
+	return ok
+}
+
+// MustHaveSymlink reports whether the current system can use os.Symlink.
+// If not, MustHaveSymlink calls t.Skip with an explanation.
+func MustHaveSymlink(t testing.TB) {
+	ok, reason := hasSymlink()
+	if !ok {
+		t.Skipf("skipping test: cannot make symlinks on %s/%s%s", runtime.GOOS, runtime.GOARCH, reason)
+	}
+}
+
+// HasLink reports whether the current system can use os.Link.
+func HasLink() bool {
+	// From Android release M (Marshmallow), hard linking files is blocked
+	// and an attempt to call link() on a file will return EACCES.
+	// - https://code.google.com/p/android-developer-preview/issues/detail?id=3150
+	return runtime.GOOS != "plan9" && runtime.GOOS != "android"
+}
+
+// MustHaveLink reports whether the current system can use os.Link.
+// If not, MustHaveLink calls t.Skip with an explanation.
+func MustHaveLink(t testing.TB) {
+	if !HasLink() {
+		t.Skipf("skipping test: hardlinks are not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
+	}
+}
+
+var flaky = flag.Bool("flaky", false, "run known-flaky tests too")
+
+func SkipFlaky(t testing.TB, issue int) {
+	t.Helper()
+	if !*flaky {
+		t.Skipf("skipping known flaky test without the -flaky flag; see golang.org/issue/%d", issue)
+	}
+}
+
+func SkipFlakyNet(t testing.TB) {
+	t.Helper()
+	if v, _ := strconv.ParseBool(os.Getenv("GO_BUILDER_FLAKY_NET")); v {
+		t.Skip("skipping test on builder known to have frequent network failures")
+	}
+}
+
+// CPUIsSlow reports whether the CPU running the test is suspected to be slow.
+func CPUIsSlow() bool {
+	switch runtime.GOARCH {
+	case "arm", "mips", "mipsle", "mips64", "mips64le":
+		return true
+	}
+	return false
+}
+
+// SkipIfShortAndSlow skips t if -short is set and the CPU running the test is
+// suspected to be slow.
+//
+// (This is useful for CPU-intensive tests that otherwise complete quickly.)
+func SkipIfShortAndSlow(t testing.TB) {
+	if testing.Short() && CPUIsSlow() {
+		t.Helper()
+		t.Skipf("skipping test in -short mode on %s", runtime.GOARCH)
+	}
+}
+
+// SkipIfOptimizationOff skips t if optimization is disabled.
+func SkipIfOptimizationOff(t testing.TB) {
+	if OptimizationOff() {
+		t.Helper()
+		t.Skip("skipping test with optimization disabled")
+	}
+}
+
+// WriteImportcfg writes an importcfg file used by the compiler or linker to
+// dstPath containing entries for the packages in std and cmd in addition
+// to the package to package file mappings in additionalPackageFiles.
+func WriteImportcfg(t testing.TB, dstPath string, additionalPackageFiles map[string]string) {
+	importcfg, err := goroot.Importcfg()
+	for k, v := range additionalPackageFiles {
+		importcfg += fmt.Sprintf("\npackagefile %s=%s", k, v)
+	}
+	if err != nil {
+		t.Fatalf("preparing the importcfg failed: %s", err)
+	}
+	err = os.WriteFile(dstPath, []byte(importcfg), 0655)
+	if err != nil {
+		t.Fatalf("writing the importcfg failed: %s", err)
+	}
+}
diff --git a/src/internal/testenv/testenv_cgo.go b/src/internal/testenv/testenv_cgo.go
new file mode 100644
index 0000000..7426a29
--- /dev/null
+++ b/src/internal/testenv/testenv_cgo.go
@@ -0,0 +1,11 @@
+// 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.
+
+//go:build cgo
+
+package testenv
+
+func init() {
+	haveCGO = true
+}
diff --git a/src/internal/testenv/testenv_notunix.go b/src/internal/testenv/testenv_notunix.go
new file mode 100644
index 0000000..180206b
--- /dev/null
+++ b/src/internal/testenv/testenv_notunix.go
@@ -0,0 +1,13 @@
+// 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.
+
+//go:build windows || plan9 || (js && wasm)
+
+package testenv
+
+import "os"
+
+// Sigquit is the signal to send to kill a hanging subprocess.
+// On Unix we send SIGQUIT, but on non-Unix we only have os.Kill.
+var Sigquit = os.Kill
diff --git a/src/internal/testenv/testenv_notwin.go b/src/internal/testenv/testenv_notwin.go
new file mode 100644
index 0000000..81171fd
--- /dev/null
+++ b/src/internal/testenv/testenv_notwin.go
@@ -0,0 +1,20 @@
+// 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.
+
+//go:build !windows
+
+package testenv
+
+import (
+	"runtime"
+)
+
+func hasSymlink() (ok bool, reason string) {
+	switch runtime.GOOS {
+	case "android", "plan9":
+		return false, ""
+	}
+
+	return true, ""
+}
diff --git a/src/internal/testenv/testenv_test.go b/src/internal/testenv/testenv_test.go
new file mode 100644
index 0000000..ebc27f1
--- /dev/null
+++ b/src/internal/testenv/testenv_test.go
@@ -0,0 +1,53 @@
+// Copyright 2022 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 testenv_test
+
+import (
+	"internal/testenv"
+	"os"
+	"path/filepath"
+	"runtime"
+	"testing"
+)
+
+func TestGoToolLocation(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	var exeSuffix string
+	if runtime.GOOS == "windows" {
+		exeSuffix = ".exe"
+	}
+
+	// Tests are defined to run within their package source directory,
+	// and this package's source directory is $GOROOT/src/internal/testenv.
+	// The 'go' command is installed at $GOROOT/bin/go, so if the environment
+	// is correct then testenv.GoTool() should be identical to ../../../bin/go.
+
+	relWant := "../../../bin/go" + exeSuffix
+	absWant, err := filepath.Abs(relWant)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	wantInfo, err := os.Stat(absWant)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("found go tool at %q (%q)", relWant, absWant)
+
+	goTool, err := testenv.GoTool()
+	if err != nil {
+		t.Fatalf("testenv.GoTool(): %v", err)
+	}
+	t.Logf("testenv.GoTool() = %q", goTool)
+
+	gotInfo, err := os.Stat(goTool)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !os.SameFile(wantInfo, gotInfo) {
+		t.Fatalf("%q is not the same file as %q", absWant, goTool)
+	}
+}
diff --git a/src/internal/testenv/testenv_unix.go b/src/internal/testenv/testenv_unix.go
new file mode 100644
index 0000000..a97e88d
--- /dev/null
+++ b/src/internal/testenv/testenv_unix.go
@@ -0,0 +1,13 @@
+// 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.
+
+//go:build unix
+
+package testenv
+
+import "syscall"
+
+// Sigquit is the signal to send to kill a hanging subprocess.
+// Send SIGQUIT to get a stack trace.
+var Sigquit = syscall.SIGQUIT
diff --git a/src/internal/testenv/testenv_windows.go b/src/internal/testenv/testenv_windows.go
new file mode 100644
index 0000000..4802b13
--- /dev/null
+++ b/src/internal/testenv/testenv_windows.go
@@ -0,0 +1,47 @@
+// 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 testenv
+
+import (
+	"os"
+	"path/filepath"
+	"sync"
+	"syscall"
+)
+
+var symlinkOnce sync.Once
+var winSymlinkErr error
+
+func initWinHasSymlink() {
+	tmpdir, err := os.MkdirTemp("", "symtest")
+	if err != nil {
+		panic("failed to create temp directory: " + err.Error())
+	}
+	defer os.RemoveAll(tmpdir)
+
+	err = os.Symlink("target", filepath.Join(tmpdir, "symlink"))
+	if err != nil {
+		err = err.(*os.LinkError).Err
+		switch err {
+		case syscall.EWINDOWS, syscall.ERROR_PRIVILEGE_NOT_HELD:
+			winSymlinkErr = err
+		}
+	}
+}
+
+func hasSymlink() (ok bool, reason string) {
+	symlinkOnce.Do(initWinHasSymlink)
+
+	switch winSymlinkErr {
+	case nil:
+		return true, ""
+	case syscall.EWINDOWS:
+		return false, ": symlinks are not supported on your version of Windows"
+	case syscall.ERROR_PRIVILEGE_NOT_HELD:
+		return false, ": you don't have enough privileges to create symlinks"
+	}
+
+	return false, ""
+}