blob: f103ad9d82e7d79a671675fdc654e97cd3b56d0f [file] [log] [blame]
// 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 (
// 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
// NeedsExec checks that the current system can start new processes
// using os.StartProcess or (more commonly) exec.Command.
// If not, NeedsExec calls t.Skip with an explanation.
func NeedsExec(t testing.TB) {
if !HasExec() {
t.Skipf("skipping test: cannot exec subprocess on %s/%s", runtime.GOOS, runtime.GOARCH)
// CommandContext is like exec.CommandContext, but:
// - skips t if the platform does not support os/exec,
// - if supported, sends SIGQUIT instead of SIGKILL in its Cancel function
// - if the test has a deadline, adds a Context timeout and (if supported) WaitDelay
// for an arbitrary grace period before the test's deadline expires,
// - if Cmd has the Cancel field, fails the test if the command is canceled
// due to the test's deadline, and
// - if supported, 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 {
var (
cancelCtx context.CancelFunc
gracePeriod time.Duration // unlimited unless the test has a deadline (to allow for interactive debugging)
if td, ok := Deadline(t); 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...)
// Use reflection to set the Cancel and WaitDelay fields, if present.
// TODO(bcmills): When we no longer support Go versions below 1.20,
// remove the use of reflect and assume that the fields are always present.
rc := reflect.ValueOf(cmd).Elem()
if rCancel := rc.FieldByName("Cancel"); rCancel.IsValid() {
rCancel.Set(reflect.ValueOf(func() error {
if cancelCtx != nil && ctx.Err() == context.DeadlineExceeded {
// The command timed out due to running too close to the test's deadline
// (because we specifically set a shorter Context deadline for that
// above). 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)
if rWaitDelay := rc.FieldByName("WaitDelay"); rWaitDelay.IsValid() {
// t.Cleanup was added in Go 1.14; for earlier Go versions,
// we just let the Context leak.
type Cleanupper interface {
if ct, ok := t.(Cleanupper); ok {
ct.Cleanup(func() {
if cancelCtx != nil {
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 {
return CommandContext(t, context.Background(), name, args...)