1 files changed, 1176 insertions, 0 deletions

diff --git a/src/os/exec/exec_test.go b/src/os/exec/exec_test.go
new file mode 100644
index 0000000..8b0c93f
--- /dev/null
+++ b/src/os/exec/exec_test.go
@@ -0,0 +1,1176 @@
+// 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.
+
+// Use an external test to avoid os/exec -> net/http -> crypto/x509 -> os/exec
+// circular dependency on non-cgo darwin.
+
+package exec_test
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"fmt"
+	"internal/poll"
+	"internal/testenv"
+	"io"
+	"log"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+)
+
+// haveUnexpectedFDs is set at init time to report whether any
+// file descriptors were open at program start.
+var haveUnexpectedFDs bool
+
+// unfinalizedFiles holds files that should not be finalized,
+// because that would close the associated file descriptor,
+// which we don't want to do.
+var unfinalizedFiles []*os.File
+
+func init() {
+	if os.Getenv("GO_WANT_HELPER_PROCESS") == "1" {
+		return
+	}
+	if runtime.GOOS == "windows" {
+		return
+	}
+	for fd := uintptr(3); fd <= 100; fd++ {
+		if poll.IsPollDescriptor(fd) {
+			continue
+		}
+		// We have no good portable way to check whether an FD is open.
+		// We use NewFile to create a *os.File, which lets us
+		// know whether it is open, but then we have to cope with
+		// the finalizer on the *os.File.
+		f := os.NewFile(fd, "")
+		if _, err := f.Stat(); err != nil {
+			// Close the file to clear the finalizer.
+			// We expect the Close to fail.
+			f.Close()
+		} else {
+			fmt.Printf("fd %d open at test start\n", fd)
+			haveUnexpectedFDs = true
+			// Use a global variable to avoid running
+			// the finalizer, which would close the FD.
+			unfinalizedFiles = append(unfinalizedFiles, f)
+		}
+	}
+}
+
+func helperCommandContext(t *testing.T, ctx context.Context, s ...string) (cmd *exec.Cmd) {
+	testenv.MustHaveExec(t)
+
+	cs := []string{"-test.run=TestHelperProcess", "--"}
+	cs = append(cs, s...)
+	if ctx != nil {
+		cmd = exec.CommandContext(ctx, os.Args[0], cs...)
+	} else {
+		cmd = exec.Command(os.Args[0], cs...)
+	}
+	cmd.Env = append(os.Environ(), "GO_WANT_HELPER_PROCESS=1")
+	return cmd
+}
+
+func helperCommand(t *testing.T, s ...string) *exec.Cmd {
+	return helperCommandContext(t, nil, s...)
+}
+
+func TestEcho(t *testing.T) {
+	bs, err := helperCommand(t, "echo", "foo bar", "baz").Output()
+	if err != nil {
+		t.Errorf("echo: %v", err)
+	}
+	if g, e := string(bs), "foo bar baz\n"; g != e {
+		t.Errorf("echo: want %q, got %q", e, g)
+	}
+}
+
+func TestCommandRelativeName(t *testing.T) {
+	testenv.MustHaveExec(t)
+
+	// Run our own binary as a relative path
+	// (e.g. "_test/exec.test") our parent directory.
+	base := filepath.Base(os.Args[0]) // "exec.test"
+	dir := filepath.Dir(os.Args[0])   // "/tmp/go-buildNNNN/os/exec/_test"
+	if dir == "." {
+		t.Skip("skipping; running test at root somehow")
+	}
+	parentDir := filepath.Dir(dir) // "/tmp/go-buildNNNN/os/exec"
+	dirBase := filepath.Base(dir)  // "_test"
+	if dirBase == "." {
+		t.Skipf("skipping; unexpected shallow dir of %q", dir)
+	}
+
+	cmd := exec.Command(filepath.Join(dirBase, base), "-test.run=TestHelperProcess", "--", "echo", "foo")
+	cmd.Dir = parentDir
+	cmd.Env = []string{"GO_WANT_HELPER_PROCESS=1"}
+
+	out, err := cmd.Output()
+	if err != nil {
+		t.Errorf("echo: %v", err)
+	}
+	if g, e := string(out), "foo\n"; g != e {
+		t.Errorf("echo: want %q, got %q", e, g)
+	}
+}
+
+func TestCatStdin(t *testing.T) {
+	// Cat, testing stdin and stdout.
+	input := "Input string\nLine 2"
+	p := helperCommand(t, "cat")
+	p.Stdin = strings.NewReader(input)
+	bs, err := p.Output()
+	if err != nil {
+		t.Errorf("cat: %v", err)
+	}
+	s := string(bs)
+	if s != input {
+		t.Errorf("cat: want %q, got %q", input, s)
+	}
+}
+
+func TestEchoFileRace(t *testing.T) {
+	cmd := helperCommand(t, "echo")
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		t.Fatalf("StdinPipe: %v", err)
+	}
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("Start: %v", err)
+	}
+	wrote := make(chan bool)
+	go func() {
+		defer close(wrote)
+		fmt.Fprint(stdin, "echo\n")
+	}()
+	if err := cmd.Wait(); err != nil {
+		t.Fatalf("Wait: %v", err)
+	}
+	<-wrote
+}
+
+func TestCatGoodAndBadFile(t *testing.T) {
+	// Testing combined output and error values.
+	bs, err := helperCommand(t, "cat", "/bogus/file.foo", "exec_test.go").CombinedOutput()
+	if _, ok := err.(*exec.ExitError); !ok {
+		t.Errorf("expected *exec.ExitError from cat combined; got %T: %v", err, err)
+	}
+	s := string(bs)
+	sp := strings.SplitN(s, "\n", 2)
+	if len(sp) != 2 {
+		t.Fatalf("expected two lines from cat; got %q", s)
+	}
+	errLine, body := sp[0], sp[1]
+	if !strings.HasPrefix(errLine, "Error: open /bogus/file.foo") {
+		t.Errorf("expected stderr to complain about file; got %q", errLine)
+	}
+	if !strings.Contains(body, "func TestHelperProcess(t *testing.T)") {
+		t.Errorf("expected test code; got %q (len %d)", body, len(body))
+	}
+}
+
+func TestNoExistExecutable(t *testing.T) {
+	// Can't run a non-existent executable
+	err := exec.Command("/no-exist-executable").Run()
+	if err == nil {
+		t.Error("expected error from /no-exist-executable")
+	}
+}
+
+func TestExitStatus(t *testing.T) {
+	// Test that exit values are returned correctly
+	cmd := helperCommand(t, "exit", "42")
+	err := cmd.Run()
+	want := "exit status 42"
+	switch runtime.GOOS {
+	case "plan9":
+		want = fmt.Sprintf("exit status: '%s %d: 42'", filepath.Base(cmd.Path), cmd.ProcessState.Pid())
+	}
+	if werr, ok := err.(*exec.ExitError); ok {
+		if s := werr.Error(); s != want {
+			t.Errorf("from exit 42 got exit %q, want %q", s, want)
+		}
+	} else {
+		t.Fatalf("expected *exec.ExitError from exit 42; got %T: %v", err, err)
+	}
+}
+
+func TestExitCode(t *testing.T) {
+	// Test that exit code are returned correctly
+	cmd := helperCommand(t, "exit", "42")
+	cmd.Run()
+	want := 42
+	if runtime.GOOS == "plan9" {
+		want = 1
+	}
+	got := cmd.ProcessState.ExitCode()
+	if want != got {
+		t.Errorf("ExitCode got %d, want %d", got, want)
+	}
+
+	cmd = helperCommand(t, "/no-exist-executable")
+	cmd.Run()
+	want = 2
+	if runtime.GOOS == "plan9" {
+		want = 1
+	}
+	got = cmd.ProcessState.ExitCode()
+	if want != got {
+		t.Errorf("ExitCode got %d, want %d", got, want)
+	}
+
+	cmd = helperCommand(t, "exit", "255")
+	cmd.Run()
+	want = 255
+	if runtime.GOOS == "plan9" {
+		want = 1
+	}
+	got = cmd.ProcessState.ExitCode()
+	if want != got {
+		t.Errorf("ExitCode got %d, want %d", got, want)
+	}
+
+	cmd = helperCommand(t, "cat")
+	cmd.Run()
+	want = 0
+	got = cmd.ProcessState.ExitCode()
+	if want != got {
+		t.Errorf("ExitCode got %d, want %d", got, want)
+	}
+
+	// Test when command does not call Run().
+	cmd = helperCommand(t, "cat")
+	want = -1
+	got = cmd.ProcessState.ExitCode()
+	if want != got {
+		t.Errorf("ExitCode got %d, want %d", got, want)
+	}
+}
+
+func TestPipes(t *testing.T) {
+	check := func(what string, err error) {
+		if err != nil {
+			t.Fatalf("%s: %v", what, err)
+		}
+	}
+	// Cat, testing stdin and stdout.
+	c := helperCommand(t, "pipetest")
+	stdin, err := c.StdinPipe()
+	check("StdinPipe", err)
+	stdout, err := c.StdoutPipe()
+	check("StdoutPipe", err)
+	stderr, err := c.StderrPipe()
+	check("StderrPipe", err)
+
+	outbr := bufio.NewReader(stdout)
+	errbr := bufio.NewReader(stderr)
+	line := func(what string, br *bufio.Reader) string {
+		line, _, err := br.ReadLine()
+		if err != nil {
+			t.Fatalf("%s: %v", what, err)
+		}
+		return string(line)
+	}
+
+	err = c.Start()
+	check("Start", err)
+
+	_, err = stdin.Write([]byte("O:I am output\n"))
+	check("first stdin Write", err)
+	if g, e := line("first output line", outbr), "O:I am output"; g != e {
+		t.Errorf("got %q, want %q", g, e)
+	}
+
+	_, err = stdin.Write([]byte("E:I am error\n"))
+	check("second stdin Write", err)
+	if g, e := line("first error line", errbr), "E:I am error"; g != e {
+		t.Errorf("got %q, want %q", g, e)
+	}
+
+	_, err = stdin.Write([]byte("O:I am output2\n"))
+	check("third stdin Write 3", err)
+	if g, e := line("second output line", outbr), "O:I am output2"; g != e {
+		t.Errorf("got %q, want %q", g, e)
+	}
+
+	stdin.Close()
+	err = c.Wait()
+	check("Wait", err)
+}
+
+const stdinCloseTestString = "Some test string."
+
+// Issue 6270.
+func TestStdinClose(t *testing.T) {
+	check := func(what string, err error) {
+		if err != nil {
+			t.Fatalf("%s: %v", what, err)
+		}
+	}
+	cmd := helperCommand(t, "stdinClose")
+	stdin, err := cmd.StdinPipe()
+	check("StdinPipe", err)
+	// Check that we can access methods of the underlying os.File.`
+	if _, ok := stdin.(interface {
+		Fd() uintptr
+	}); !ok {
+		t.Error("can't access methods of underlying *os.File")
+	}
+	check("Start", cmd.Start())
+	go func() {
+		_, err := io.Copy(stdin, strings.NewReader(stdinCloseTestString))
+		check("Copy", err)
+		// Before the fix, this next line would race with cmd.Wait.
+		check("Close", stdin.Close())
+	}()
+	check("Wait", cmd.Wait())
+}
+
+// Issue 17647.
+// It used to be the case that TestStdinClose, above, would fail when
+// run under the race detector. This test is a variant of TestStdinClose
+// that also used to fail when run under the race detector.
+// This test is run by cmd/dist under the race detector to verify that
+// the race detector no longer reports any problems.
+func TestStdinCloseRace(t *testing.T) {
+	cmd := helperCommand(t, "stdinClose")
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		t.Fatalf("StdinPipe: %v", err)
+	}
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("Start: %v", err)
+	}
+	go func() {
+		// We don't check the error return of Kill. It is
+		// possible that the process has already exited, in
+		// which case Kill will return an error "process
+		// already finished". The purpose of this test is to
+		// see whether the race detector reports an error; it
+		// doesn't matter whether this Kill succeeds or not.
+		cmd.Process.Kill()
+	}()
+	go func() {
+		// Send the wrong string, so that the child fails even
+		// if the other goroutine doesn't manage to kill it first.
+		// This test is to check that the race detector does not
+		// falsely report an error, so it doesn't matter how the
+		// child process fails.
+		io.Copy(stdin, strings.NewReader("unexpected string"))
+		if err := stdin.Close(); err != nil {
+			t.Errorf("stdin.Close: %v", err)
+		}
+	}()
+	if err := cmd.Wait(); err == nil {
+		t.Fatalf("Wait: succeeded unexpectedly")
+	}
+}
+
+// Issue 5071
+func TestPipeLookPathLeak(t *testing.T) {
+	// If we are reading from /proc/self/fd we (should) get an exact result.
+	tolerance := 0
+
+	// Reading /proc/self/fd is more reliable than calling lsof, so try that
+	// first.
+	numOpenFDs := func() (int, []byte, error) {
+		fds, err := os.ReadDir("/proc/self/fd")
+		if err != nil {
+			return 0, nil, err
+		}
+		return len(fds), nil, nil
+	}
+	want, before, err := numOpenFDs()
+	if err != nil {
+		// We encountered a problem reading /proc/self/fd (we might be on
+		// a platform that doesn't have it). Fall back onto lsof.
+		t.Logf("using lsof because: %v", err)
+		numOpenFDs = func() (int, []byte, error) {
+			// Android's stock lsof does not obey the -p option,
+			// so extra filtering is needed.
+			// https://golang.org/issue/10206
+			if runtime.GOOS == "android" {
+				// numOpenFDsAndroid handles errors itself and
+				// might skip or fail the test.
+				n, lsof := numOpenFDsAndroid(t)
+				return n, lsof, nil
+			}
+			lsof, err := exec.Command("lsof", "-b", "-n", "-p", strconv.Itoa(os.Getpid())).Output()
+			return bytes.Count(lsof, []byte("\n")), lsof, err
+		}
+
+		// lsof may see file descriptors associated with the fork itself,
+		// so we allow some extra margin if we have to use it.
+		// https://golang.org/issue/19243
+		tolerance = 5
+
+		// Retry reading the number of open file descriptors.
+		want, before, err = numOpenFDs()
+		if err != nil {
+			t.Log(err)
+			t.Skipf("skipping test; error finding or running lsof")
+		}
+	}
+
+	for i := 0; i < 6; i++ {
+		cmd := exec.Command("something-that-does-not-exist-executable")
+		cmd.StdoutPipe()
+		cmd.StderrPipe()
+		cmd.StdinPipe()
+		if err := cmd.Run(); err == nil {
+			t.Fatal("unexpected success")
+		}
+	}
+	got, after, err := numOpenFDs()
+	if err != nil {
+		// numOpenFDs has already succeeded once, it should work here.
+		t.Errorf("unexpected failure: %v", err)
+	}
+	if got-want > tolerance {
+		t.Errorf("number of open file descriptors changed: got %v, want %v", got, want)
+		if before != nil {
+			t.Errorf("before:\n%v\n", before)
+		}
+		if after != nil {
+			t.Errorf("after:\n%v\n", after)
+		}
+	}
+}
+
+func numOpenFDsAndroid(t *testing.T) (n int, lsof []byte) {
+	raw, err := exec.Command("lsof").Output()
+	if err != nil {
+		t.Skip("skipping test; error finding or running lsof")
+	}
+
+	// First find the PID column index by parsing the first line, and
+	// select lines containing pid in the column.
+	pid := []byte(strconv.Itoa(os.Getpid()))
+	pidCol := -1
+
+	s := bufio.NewScanner(bytes.NewReader(raw))
+	for s.Scan() {
+		line := s.Bytes()
+		fields := bytes.Fields(line)
+		if pidCol < 0 {
+			for i, v := range fields {
+				if bytes.Equal(v, []byte("PID")) {
+					pidCol = i
+					break
+				}
+			}
+			lsof = append(lsof, line...)
+			continue
+		}
+		if bytes.Equal(fields[pidCol], pid) {
+			lsof = append(lsof, '\n')
+			lsof = append(lsof, line...)
+		}
+	}
+	if pidCol < 0 {
+		t.Fatal("error processing lsof output: unexpected header format")
+	}
+	if err := s.Err(); err != nil {
+		t.Fatalf("error processing lsof output: %v", err)
+	}
+	return bytes.Count(lsof, []byte("\n")), lsof
+}
+
+func TestExtraFilesFDShuffle(t *testing.T) {
+	t.Skip("flaky test; see https://golang.org/issue/5780")
+	switch runtime.GOOS {
+	case "windows":
+		t.Skip("no operating system support; skipping")
+	}
+
+	// syscall.StartProcess maps all the FDs passed to it in
+	// ProcAttr.Files (the concatenation of stdin,stdout,stderr and
+	// ExtraFiles) into consecutive FDs in the child, that is:
+	// Files{11, 12, 6, 7, 9, 3} should result in the file
+	// represented by FD 11 in the parent being made available as 0
+	// in the child, 12 as 1, etc.
+	//
+	// We want to test that FDs in the child do not get overwritten
+	// by one another as this shuffle occurs. The original implementation
+	// was buggy in that in some data dependent cases it would overwrite
+	// stderr in the child with one of the ExtraFile members.
+	// Testing for this case is difficult because it relies on using
+	// the same FD values as that case. In particular, an FD of 3
+	// must be at an index of 4 or higher in ProcAttr.Files and
+	// the FD of the write end of the Stderr pipe (as obtained by
+	// StderrPipe()) must be the same as the size of ProcAttr.Files;
+	// therefore we test that the read end of this pipe (which is what
+	// is returned to the parent by StderrPipe() being one less than
+	// the size of ProcAttr.Files, i.e. 3+len(cmd.ExtraFiles).
+	//
+	// Moving this test case around within the overall tests may
+	// affect the FDs obtained and hence the checks to catch these cases.
+	npipes := 2
+	c := helperCommand(t, "extraFilesAndPipes", strconv.Itoa(npipes+1))
+	rd, wr, _ := os.Pipe()
+	defer rd.Close()
+	if rd.Fd() != 3 {
+		t.Errorf("bad test value for test pipe: fd %d", rd.Fd())
+	}
+	stderr, _ := c.StderrPipe()
+	wr.WriteString("_LAST")
+	wr.Close()
+
+	pipes := make([]struct {
+		r, w *os.File
+	}, npipes)
+	data := []string{"a", "b"}
+
+	for i := 0; i < npipes; i++ {
+		r, w, err := os.Pipe()
+		if err != nil {
+			t.Fatalf("unexpected error creating pipe: %s", err)
+		}
+		pipes[i].r = r
+		pipes[i].w = w
+		w.WriteString(data[i])
+		c.ExtraFiles = append(c.ExtraFiles, pipes[i].r)
+		defer func() {
+			r.Close()
+			w.Close()
+		}()
+	}
+	// Put fd 3 at the end.
+	c.ExtraFiles = append(c.ExtraFiles, rd)
+
+	stderrFd := int(stderr.(*os.File).Fd())
+	if stderrFd != ((len(c.ExtraFiles) + 3) - 1) {
+		t.Errorf("bad test value for stderr pipe")
+	}
+
+	expected := "child: " + strings.Join(data, "") + "_LAST"
+
+	err := c.Start()
+	if err != nil {
+		t.Fatalf("Run: %v", err)
+	}
+	ch := make(chan string, 1)
+	go func(ch chan string) {
+		buf := make([]byte, 512)
+		n, err := stderr.Read(buf)
+		if err != nil {
+			t.Errorf("Read: %s", err)
+			ch <- err.Error()
+		} else {
+			ch <- string(buf[:n])
+		}
+		close(ch)
+	}(ch)
+	select {
+	case m := <-ch:
+		if m != expected {
+			t.Errorf("Read: '%s' not '%s'", m, expected)
+		}
+	case <-time.After(5 * time.Second):
+		t.Errorf("Read timedout")
+	}
+	c.Wait()
+}
+
+func TestExtraFiles(t *testing.T) {
+	if haveUnexpectedFDs {
+		// The point of this test is to make sure that any
+		// descriptors we open are marked close-on-exec.
+		// If haveUnexpectedFDs is true then there were other
+		// descriptors open when we started the test,
+		// so those descriptors are clearly not close-on-exec,
+		// and they will confuse the test. We could modify
+		// the test to expect those descriptors to remain open,
+		// but since we don't know where they came from or what
+		// they are doing, that seems fragile. For example,
+		// perhaps they are from the startup code on this
+		// system for some reason. Also, this test is not
+		// system-specific; as long as most systems do not skip
+		// the test, we will still be testing what we care about.
+		t.Skip("skipping test because test was run with FDs open")
+	}
+
+	testenv.MustHaveExec(t)
+	testenv.MustHaveGoBuild(t)
+
+	// This test runs with cgo disabled. External linking needs cgo, so
+	// it doesn't work if external linking is required.
+	testenv.MustInternalLink(t)
+
+	if runtime.GOOS == "windows" {
+		t.Skipf("skipping test on %q", runtime.GOOS)
+	}
+
+	// Force network usage, to verify the epoll (or whatever) fd
+	// doesn't leak to the child,
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ln.Close()
+
+	// Make sure duplicated fds don't leak to the child.
+	f, err := ln.(*net.TCPListener).File()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	ln2, err := net.FileListener(f)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ln2.Close()
+
+	// Force TLS root certs to be loaded (which might involve
+	// cgo), to make sure none of that potential C code leaks fds.
+	ts := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
+	// quiet expected TLS handshake error "remote error: bad certificate"
+	ts.Config.ErrorLog = log.New(io.Discard, "", 0)
+	ts.StartTLS()
+	defer ts.Close()
+	_, err = http.Get(ts.URL)
+	if err == nil {
+		t.Errorf("success trying to fetch %s; want an error", ts.URL)
+	}
+
+	tf, err := os.CreateTemp("", "")
+	if err != nil {
+		t.Fatalf("TempFile: %v", err)
+	}
+	defer os.Remove(tf.Name())
+	defer tf.Close()
+
+	const text = "Hello, fd 3!"
+	_, err = tf.Write([]byte(text))
+	if err != nil {
+		t.Fatalf("Write: %v", err)
+	}
+	_, err = tf.Seek(0, io.SeekStart)
+	if err != nil {
+		t.Fatalf("Seek: %v", err)
+	}
+
+	tempdir := t.TempDir()
+	exe := filepath.Join(tempdir, "read3.exe")
+
+	c := exec.Command(testenv.GoToolPath(t), "build", "-o", exe, "read3.go")
+	// Build the test without cgo, so that C library functions don't
+	// open descriptors unexpectedly. See issue 25628.
+	c.Env = append(os.Environ(), "CGO_ENABLED=0")
+	if output, err := c.CombinedOutput(); err != nil {
+		t.Logf("go build -o %s read3.go\n%s", exe, output)
+		t.Fatalf("go build failed: %v", err)
+	}
+
+	// Use a deadline to try to get some output even if the program hangs.
+	ctx := context.Background()
+	if deadline, ok := t.Deadline(); ok {
+		// Leave a 20% grace period to flush output, which may be large on the
+		// linux/386 builders because we're running the subprocess under strace.
+		deadline = deadline.Add(-time.Until(deadline) / 5)
+
+		var cancel context.CancelFunc
+		ctx, cancel = context.WithDeadline(ctx, deadline)
+		defer cancel()
+	}
+
+	c = exec.CommandContext(ctx, exe)
+	var stdout, stderr bytes.Buffer
+	c.Stdout = &stdout
+	c.Stderr = &stderr
+	c.ExtraFiles = []*os.File{tf}
+	if runtime.GOOS == "illumos" {
+		// Some facilities in illumos are implemented via access
+		// to /proc by libc; such accesses can briefly occupy a
+		// low-numbered fd.  If this occurs concurrently with the
+		// test that checks for leaked descriptors, the check can
+		// become confused and report a spurious leaked descriptor.
+		// (See issue #42431 for more detailed analysis.)
+		//
+		// Attempt to constrain the use of additional threads in the
+		// child process to make this test less flaky:
+		c.Env = append(os.Environ(), "GOMAXPROCS=1")
+	}
+	err = c.Run()
+	if err != nil {
+		t.Fatalf("Run: %v\n--- stdout:\n%s--- stderr:\n%s", err, stdout.Bytes(), stderr.Bytes())
+	}
+	if stdout.String() != text {
+		t.Errorf("got stdout %q, stderr %q; want %q on stdout", stdout.String(), stderr.String(), text)
+	}
+}
+
+func TestExtraFilesRace(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("no operating system support; skipping")
+	}
+	listen := func() net.Listener {
+		ln, err := net.Listen("tcp", "127.0.0.1:0")
+		if err != nil {
+			t.Fatal(err)
+		}
+		return ln
+	}
+	listenerFile := func(ln net.Listener) *os.File {
+		f, err := ln.(*net.TCPListener).File()
+		if err != nil {
+			t.Fatal(err)
+		}
+		return f
+	}
+	runCommand := func(c *exec.Cmd, out chan<- string) {
+		bout, err := c.CombinedOutput()
+		if err != nil {
+			out <- "ERROR:" + err.Error()
+		} else {
+			out <- string(bout)
+		}
+	}
+
+	for i := 0; i < 10; i++ {
+		if testing.Short() && i >= 3 {
+			break
+		}
+		la := listen()
+		ca := helperCommand(t, "describefiles")
+		ca.ExtraFiles = []*os.File{listenerFile(la)}
+		lb := listen()
+		cb := helperCommand(t, "describefiles")
+		cb.ExtraFiles = []*os.File{listenerFile(lb)}
+		ares := make(chan string)
+		bres := make(chan string)
+		go runCommand(ca, ares)
+		go runCommand(cb, bres)
+		if got, want := <-ares, fmt.Sprintf("fd3: listener %s\n", la.Addr()); got != want {
+			t.Errorf("iteration %d, process A got:\n%s\nwant:\n%s\n", i, got, want)
+		}
+		if got, want := <-bres, fmt.Sprintf("fd3: listener %s\n", lb.Addr()); got != want {
+			t.Errorf("iteration %d, process B got:\n%s\nwant:\n%s\n", i, got, want)
+		}
+		la.Close()
+		lb.Close()
+		for _, f := range ca.ExtraFiles {
+			f.Close()
+		}
+		for _, f := range cb.ExtraFiles {
+			f.Close()
+		}
+
+	}
+}
+
+// TestHelperProcess isn't a real test. It's used as a helper process
+// for TestParameterRun.
+func TestHelperProcess(*testing.T) {
+	if os.Getenv("GO_WANT_HELPER_PROCESS") != "1" {
+		return
+	}
+	defer os.Exit(0)
+
+	args := os.Args
+	for len(args) > 0 {
+		if args[0] == "--" {
+			args = args[1:]
+			break
+		}
+		args = args[1:]
+	}
+	if len(args) == 0 {
+		fmt.Fprintf(os.Stderr, "No command\n")
+		os.Exit(2)
+	}
+
+	cmd, args := args[0], args[1:]
+	switch cmd {
+	case "echo":
+		iargs := []interface{}{}
+		for _, s := range args {
+			iargs = append(iargs, s)
+		}
+		fmt.Println(iargs...)
+	case "echoenv":
+		for _, s := range args {
+			fmt.Println(os.Getenv(s))
+		}
+		os.Exit(0)
+	case "cat":
+		if len(args) == 0 {
+			io.Copy(os.Stdout, os.Stdin)
+			return
+		}
+		exit := 0
+		for _, fn := range args {
+			f, err := os.Open(fn)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+				exit = 2
+			} else {
+				defer f.Close()
+				io.Copy(os.Stdout, f)
+			}
+		}
+		os.Exit(exit)
+	case "pipetest":
+		bufr := bufio.NewReader(os.Stdin)
+		for {
+			line, _, err := bufr.ReadLine()
+			if err == io.EOF {
+				break
+			} else if err != nil {
+				os.Exit(1)
+			}
+			if bytes.HasPrefix(line, []byte("O:")) {
+				os.Stdout.Write(line)
+				os.Stdout.Write([]byte{'\n'})
+			} else if bytes.HasPrefix(line, []byte("E:")) {
+				os.Stderr.Write(line)
+				os.Stderr.Write([]byte{'\n'})
+			} else {
+				os.Exit(1)
+			}
+		}
+	case "stdinClose":
+		b, err := io.ReadAll(os.Stdin)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+			os.Exit(1)
+		}
+		if s := string(b); s != stdinCloseTestString {
+			fmt.Fprintf(os.Stderr, "Error: Read %q, want %q", s, stdinCloseTestString)
+			os.Exit(1)
+		}
+		os.Exit(0)
+	case "exit":
+		n, _ := strconv.Atoi(args[0])
+		os.Exit(n)
+	case "describefiles":
+		f := os.NewFile(3, fmt.Sprintf("fd3"))
+		ln, err := net.FileListener(f)
+		if err == nil {
+			fmt.Printf("fd3: listener %s\n", ln.Addr())
+			ln.Close()
+		}
+		os.Exit(0)
+	case "extraFilesAndPipes":
+		n, _ := strconv.Atoi(args[0])
+		pipes := make([]*os.File, n)
+		for i := 0; i < n; i++ {
+			pipes[i] = os.NewFile(uintptr(3+i), strconv.Itoa(i))
+		}
+		response := ""
+		for i, r := range pipes {
+			ch := make(chan string, 1)
+			go func(c chan string) {
+				buf := make([]byte, 10)
+				n, err := r.Read(buf)
+				if err != nil {
+					fmt.Fprintf(os.Stderr, "Child: read error: %v on pipe %d\n", err, i)
+					os.Exit(1)
+				}
+				c <- string(buf[:n])
+				close(c)
+			}(ch)
+			select {
+			case m := <-ch:
+				response = response + m
+			case <-time.After(5 * time.Second):
+				fmt.Fprintf(os.Stderr, "Child: Timeout reading from pipe: %d\n", i)
+				os.Exit(1)
+			}
+		}
+		fmt.Fprintf(os.Stderr, "child: %s", response)
+		os.Exit(0)
+	case "exec":
+		cmd := exec.Command(args[1])
+		cmd.Dir = args[0]
+		output, err := cmd.CombinedOutput()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Child: %s %s", err, string(output))
+			os.Exit(1)
+		}
+		fmt.Printf("%s", string(output))
+		os.Exit(0)
+	case "lookpath":
+		p, err := exec.LookPath(args[0])
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "LookPath failed: %v\n", err)
+			os.Exit(1)
+		}
+		fmt.Print(p)
+		os.Exit(0)
+	case "stderrfail":
+		fmt.Fprintf(os.Stderr, "some stderr text\n")
+		os.Exit(1)
+	case "sleep":
+		time.Sleep(3 * time.Second)
+		os.Exit(0)
+	default:
+		fmt.Fprintf(os.Stderr, "Unknown command %q\n", cmd)
+		os.Exit(2)
+	}
+}
+
+type delayedInfiniteReader struct{}
+
+func (delayedInfiniteReader) Read(b []byte) (int, error) {
+	time.Sleep(100 * time.Millisecond)
+	for i := range b {
+		b[i] = 'x'
+	}
+	return len(b), nil
+}
+
+// Issue 9173: ignore stdin pipe writes if the program completes successfully.
+func TestIgnorePipeErrorOnSuccess(t *testing.T) {
+	testenv.MustHaveExec(t)
+
+	testWith := func(r io.Reader) func(*testing.T) {
+		return func(t *testing.T) {
+			cmd := helperCommand(t, "echo", "foo")
+			var out bytes.Buffer
+			cmd.Stdin = r
+			cmd.Stdout = &out
+			if err := cmd.Run(); err != nil {
+				t.Fatal(err)
+			}
+			if got, want := out.String(), "foo\n"; got != want {
+				t.Errorf("output = %q; want %q", got, want)
+			}
+		}
+	}
+	t.Run("10MB", testWith(strings.NewReader(strings.Repeat("x", 10<<20))))
+	t.Run("Infinite", testWith(delayedInfiniteReader{}))
+}
+
+type badWriter struct{}
+
+func (w *badWriter) Write(data []byte) (int, error) {
+	return 0, io.ErrUnexpectedEOF
+}
+
+func TestClosePipeOnCopyError(t *testing.T) {
+	testenv.MustHaveExec(t)
+
+	if runtime.GOOS == "windows" || runtime.GOOS == "plan9" {
+		t.Skipf("skipping test on %s - no yes command", runtime.GOOS)
+	}
+	cmd := exec.Command("yes")
+	cmd.Stdout = new(badWriter)
+	c := make(chan int, 1)
+	go func() {
+		err := cmd.Run()
+		if err == nil {
+			t.Errorf("yes completed successfully")
+		}
+		c <- 1
+	}()
+	select {
+	case <-c:
+		// ok
+	case <-time.After(5 * time.Second):
+		t.Fatalf("yes got stuck writing to bad writer")
+	}
+}
+
+func TestOutputStderrCapture(t *testing.T) {
+	testenv.MustHaveExec(t)
+
+	cmd := helperCommand(t, "stderrfail")
+	_, err := cmd.Output()
+	ee, ok := err.(*exec.ExitError)
+	if !ok {
+		t.Fatalf("Output error type = %T; want ExitError", err)
+	}
+	got := string(ee.Stderr)
+	want := "some stderr text\n"
+	if got != want {
+		t.Errorf("ExitError.Stderr = %q; want %q", got, want)
+	}
+}
+
+func TestContext(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	c := helperCommandContext(t, ctx, "pipetest")
+	stdin, err := c.StdinPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	stdout, err := c.StdoutPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := c.Start(); err != nil {
+		t.Fatal(err)
+	}
+
+	if _, err := stdin.Write([]byte("O:hi\n")); err != nil {
+		t.Fatal(err)
+	}
+	buf := make([]byte, 5)
+	n, err := io.ReadFull(stdout, buf)
+	if n != len(buf) || err != nil || string(buf) != "O:hi\n" {
+		t.Fatalf("ReadFull = %d, %v, %q", n, err, buf[:n])
+	}
+	waitErr := make(chan error, 1)
+	go func() {
+		waitErr <- c.Wait()
+	}()
+	cancel()
+	select {
+	case err := <-waitErr:
+		if err == nil {
+			t.Fatal("expected Wait failure")
+		}
+	case <-time.After(3 * time.Second):
+		t.Fatal("timeout waiting for child process death")
+	}
+}
+
+func TestContextCancel(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	c := helperCommandContext(t, ctx, "cat")
+
+	r, w, err := os.Pipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	c.Stdin = r
+
+	stdout, err := c.StdoutPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	readDone := make(chan struct{})
+	go func() {
+		defer close(readDone)
+		var a [1024]byte
+		for {
+			n, err := stdout.Read(a[:])
+			if err != nil {
+				if err != io.EOF {
+					t.Errorf("unexpected read error: %v", err)
+				}
+				return
+			}
+			t.Logf("%s", a[:n])
+		}
+	}()
+
+	if err := c.Start(); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := r.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	if _, err := io.WriteString(w, "echo"); err != nil {
+		t.Fatal(err)
+	}
+
+	cancel()
+
+	// Calling cancel should have killed the process, so writes
+	// should now fail.  Give the process a little while to die.
+	start := time.Now()
+	for {
+		if _, err := io.WriteString(w, "echo"); err != nil {
+			break
+		}
+		if time.Since(start) > time.Second {
+			t.Fatal("canceling context did not stop program")
+		}
+		time.Sleep(time.Millisecond)
+	}
+
+	if err := w.Close(); err != nil {
+		t.Errorf("error closing write end of pipe: %v", err)
+	}
+	<-readDone
+
+	if err := c.Wait(); err == nil {
+		t.Error("program unexpectedly exited successfully")
+	} else {
+		t.Logf("exit status: %v", err)
+	}
+}
+
+// test that environment variables are de-duped.
+func TestDedupEnvEcho(t *testing.T) {
+	testenv.MustHaveExec(t)
+
+	cmd := helperCommand(t, "echoenv", "FOO")
+	cmd.Env = append(cmd.Env, "FOO=bad", "FOO=good")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got, want := strings.TrimSpace(string(out)), "good"; got != want {
+		t.Errorf("output = %q; want %q", got, want)
+	}
+}
+
+func TestString(t *testing.T) {
+	echoPath, err := exec.LookPath("echo")
+	if err != nil {
+		t.Skip(err)
+	}
+	tests := [...]struct {
+		path string
+		args []string
+		want string
+	}{
+		{"echo", nil, echoPath},
+		{"echo", []string{"a"}, echoPath + " a"},
+		{"echo", []string{"a", "b"}, echoPath + " a b"},
+	}
+	for _, test := range tests {
+		cmd := exec.Command(test.path, test.args...)
+		if got := cmd.String(); got != test.want {
+			t.Errorf("String(%q, %q) = %q, want %q", test.path, test.args, got, test.want)
+		}
+	}
+}
+
+func TestStringPathNotResolved(t *testing.T) {
+	_, err := exec.LookPath("makemeasandwich")
+	if err == nil {
+		t.Skip("wow, thanks")
+	}
+	cmd := exec.Command("makemeasandwich", "-lettuce")
+	want := "makemeasandwich -lettuce"
+	if got := cmd.String(); got != want {
+		t.Errorf("String(%q, %q) = %q, want %q", "makemeasandwich", "-lettuce", got, want)
+	}
+}
+
+// start a child process without the user code explicitly starting
+// with a copy of the parent's. (The Windows SYSTEMROOT issue: Issue
+// 25210)
+func TestChildCriticalEnv(t *testing.T) {
+	testenv.MustHaveExec(t)
+	if runtime.GOOS != "windows" {
+		t.Skip("only testing on Windows")
+	}
+	cmd := helperCommand(t, "echoenv", "SYSTEMROOT")
+	cmd.Env = []string{"GO_WANT_HELPER_PROCESS=1"}
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if strings.TrimSpace(string(out)) == "" {
+		t.Error("no SYSTEMROOT found")
+	}
+}