testing: testing: add (*T).Deadline method for test timeout

Fixes #28135

Change-Id: I62818595eaf4a59d8b5c26cd6848c08fec795ad1
Reviewed-on: https://go-review.googlesource.com/c/go/+/202758
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

api/next.txt

@@ -0,0 +1 @@
+pkg testing, method (*T) Deadline() (time.Time, bool)

doc/go1.15.html

@@ -60,6 +60,15 @@ TODO
 TODO
 </p>
 
+<dl id="testing"><dt><a href="/pkg/testing/">testing</a></dt>
+  <dd>
+    <p><!-- golang.org/issue/28135 -->
+      The <code>testing.T</code> type now has a <code>Deadline</code> method
+      that reports the time at which the test binary will have exceeded its
+      timeout.
+    </p>
+</dl><!-- testing -->
+
 <h3 id="minor_library_changes">Minor changes to the library</h3>
 
 <p>

src/cmd/go/testdata/script/test_deadline.txt

@@ -0,0 +1,50 @@
+[short] skip
+
+go test -timeout=0 -run=TestNoDeadline
+go test -timeout=1m -run=TestDeadlineWithinMinute
+go test -timeout=1m -run=TestSubtestDeadlineWithinMinute
+
+-- deadline_test.go --
+package testing_test
+
+import (
+	"testing"
+	"time"
+)
+
+func TestNoDeadline(t *testing.T) {
+	d, ok := t.Deadline()
+	if ok || !d.IsZero() {
+		t.Fatalf("t.Deadline() = %v, %v; want 0, false", d, ok)
+	}
+}
+
+func TestDeadlineWithinMinute(t *testing.T) {
+	now := time.Now()
+	d, ok := t.Deadline()
+	if !ok || d.IsZero() {
+		t.Fatalf("t.Deadline() = %v, %v; want nonzero deadline", d, ok)
+	}
+	if !d.After(now) {
+		t.Fatalf("t.Deadline() = %v; want after start of test (%v)", d, now)
+	}
+	if d.Sub(now) > time.Minute {
+		t.Fatalf("t.Deadline() = %v; want within one minute of start of test (%v)", d, now)
+	}
+}
+
+func TestSubtestDeadlineWithinMinute(t *testing.T) {
+	t.Run("sub", func(t *testing.T) {
+		now := time.Now()
+		d, ok := t.Deadline()
+		if !ok || d.IsZero() {
+			t.Fatalf("t.Deadline() = %v, %v; want nonzero deadline", d, ok)
+		}
+		if !d.After(now) {
+			t.Fatalf("t.Deadline() = %v; want after start of test (%v)", d, now)
+		}
+		if d.Sub(now) > time.Minute {
+			t.Fatalf("t.Deadline() = %v; want within one minute of start of test (%v)", d, now)
+		}
+	})
+}

src/testing/testing.go

@@ -1049,10 +1049,20 @@ func (t *T) Run(name string, f func(t *T)) bool {
 	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
 
@@ -1195,9 +1205,9 @@ func (m *M) Run() int {
 
 	m.before()
 	defer m.after()
-	m.startAlarm()
+	deadline := m.startAlarm()
 	haveExamples = len(m.examples) > 0
-	testRan, testOk := runTests(m.deps.MatchString, m.tests)
+	testRan, testOk := runTests(m.deps.MatchString, m.tests, deadline)
 	exampleRan, exampleOk := runExamples(m.deps.MatchString, m.examples)
 	m.stopAlarm()
 	if !testRan && !exampleRan && *matchBenchmarks == "" {
@@ -1255,14 +1265,18 @@ func listTests(matchString func(pat, str string) (bool, error), tests []Internal
 // 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) {
-	ran, ok := runTests(matchString, tests)
+	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) (ran, ok bool) {
+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)
@@ -1271,6 +1285,7 @@ func runTests(matchString func(pat, str string) (bool, error), tests []InternalT
 				break
 			}
 			ctx := newTestContext(*parallel, newMatcher(matchString, *match, "-test.run"))
+			ctx.deadline = deadline
 			t := &T{
 				common: common{
 					signal:  make(chan bool),
@@ -1452,14 +1467,18 @@ func toOutputDir(path string) string {
 }
 
 // startAlarm starts an alarm if requested.
-func (m *M) startAlarm() {
-	if *timeout > 0 {
+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.