time: deflake TestChan/asynctimerchan=1 tests

The overall time package tests increase from 3.85s to 4.85s on my laptop.
But they should be less flaky, and the time is spent sleeping, so it won't
slow down the overall machine running multiple package tests in
parallel.

For #66322.

Change-Id: I66d6647c389c943b53045e8836ede4ba3d4670c7
Reviewed-on: https://go-review.googlesource.com/c/go/+/581315
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: rsc

src/time/tick_test.go

@@ -55,11 +55,11 @@ func TestTicker(t *testing.T) {
 		count, delta := test.count, test.delta
 		ticker := NewTicker(delta)
 		t0 := Now()
-		for i := 0; i < count/2; i++ {
+		for range count / 2 {
 			<-ticker.C
 		}
 		ticker.Reset(delta * 2)
-		for i := count / 2; i < count; i++ {
+		for range count - count/2 {
 			<-ticker.C
 		}
 		ticker.Stop()
@@ -114,7 +114,7 @@ func TestTeardown(t *testing.T) {
 	if testing.Short() {
 		Delta = 20 * Millisecond
 	}
-	for i := 0; i < 3; i++ {
+	for range 3 {
 		ticker := NewTicker(Delta)
 		<-ticker.C
 		ticker.Stop()
@@ -356,14 +356,19 @@ func testTimerChan(t *testing.T, tim timer, C <-chan Time, synctimerchan bool) {
 	// Windows in particular has very coarse timers so we have to
 	// wait 10ms just to make a timer go off.
 	const (
-		sched = 10 * Millisecond
-		tries = 100
+		sched      = 10 * Millisecond
+		tries      = 100
+		drainTries = 5
 	)
 
 	drain := func() {
-		select {
-		case <-C:
-		default:
+		for range drainTries {
+			select {
+			case <-C:
+				return
+			default:
+			}
+			Sleep(sched)
 		}
 	}
 	noTick := func() {
@@ -381,7 +386,7 @@ func testTimerChan(t *testing.T, tim timer, C <-chan Time, synctimerchan bool) {
 		case <-C:
 			return
 		}
-		for i := 0; i < tries; i++ {
+		for range tries {
 			Sleep(sched)
 			select {
 			default:
@@ -403,7 +408,7 @@ func testTimerChan(t *testing.T, tim timer, C <-chan Time, synctimerchan bool) {
 		if n = len(C); n == 1 {
 			return
 		}
-		for i := 0; i < tries; i++ {
+		for range tries {
 			Sleep(sched)
 			if n = len(C); n == 1 {
 				return
@@ -477,7 +482,7 @@ func testTimerChan(t *testing.T, tim timer, C <-chan Time, synctimerchan bool) {
 
 	waitDone := func(done chan bool) {
 		t.Helper()
-		for i := 0; i < tries; i++ {
+		for range tries {
 			Sleep(sched)
 			select {
 			case <-done:
@@ -580,7 +585,7 @@ func testTimerChan(t *testing.T, tim timer, C <-chan Time, synctimerchan bool) {
 	// Test enqueueTimerChan when timer is stopped.
 	stop = make(chan bool)
 	done = make(chan bool, 2)
-	for i := 0; i < 2; i++ {
+	for range 2 {
 		go func() {
 			select {
 			case <-C:
@@ -641,7 +646,7 @@ func TestAfterTimes(t *testing.T) {
 	// Make sure it does.
 	// To avoid flakes due to very long scheduling delays,
 	// require 10 failures in a row before deciding something is wrong.
-	for i := 0; i < 10; i++ {
+	for range 10 {
 		start := Now()
 		c := After(10 * Millisecond)
 		Sleep(500 * Millisecond)
@@ -657,7 +662,7 @@ func TestAfterTimes(t *testing.T) {
 func TestTickTimes(t *testing.T) {
 	t.Parallel()
 	// See comment in TestAfterTimes
-	for i := 0; i < 10; i++ {
+	for range 10 {
 		start := Now()
 		c := Tick(10 * Millisecond)
 		Sleep(500 * Millisecond)