blob: 4bacdc3ce87e31aa0adb2af51b2d4e15c2a0bfb1 [file] [log] [blame]
// Copyright 2023 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 (
// 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 {
var (
cancelCtx context.CancelFunc
gracePeriod time.Duration // unlimited unless the test has a deadline (to allow for interactive debugging)
if t, ok := t.(interface {
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...)
// Set the Cancel and WaitDelay fields only if present (go 1.20 and later).
// TODO: When Go 1.19 is no longer supported, remove this use of reflection
// and instead set the fields directly.
if cmdCancel := reflect.ValueOf(cmd).Elem().FieldByName("Cancel"); cmdCancel.IsValid() {
cmdCancel.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.
// 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 cmdWaitDelay := reflect.ValueOf(cmd).Elem().FieldByName("WaitDelay"); cmdWaitDelay.IsValid() {
t.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...)