time: replace time.Now().Sub call with time.Since in test

Change-Id: I56ca2d11637d60c6b0656fdc1d900a2384aba141
GitHub-Last-Rev: 686e02d
GitHub-Pull-Request: #66264
Reviewed-on: https://go-review.googlesource.com/c/go/+/570916
Reviewed-by: qiulaidongfeng <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: testwill

src/time/sleep_test.go

@@ -63,7 +63,7 @@ func TestSleep(t *testing.T) {
 	start := Now()
 	Sleep(delay)
 	delayadj := adjustDelay(t, delay)
-	duration := Now().Sub(start)
+	duration := Since(start)
 	if duration < delayadj {
 		t.Fatalf("Sleep(%s) slept for only %s", delay, duration)
 	}
@@ -322,7 +322,7 @@ func TestAfter(t *testing.T) {
 	start := Now()
 	end := <-After(delay)
 	delayadj := adjustDelay(t, delay)
-	if duration := Now().Sub(start); duration < delayadj {
+	if duration := Since(start); duration < delayadj {
 		t.Fatalf("After(%s) slept for only %d ns", delay, duration)
 	}
 	if min := start.Add(delayadj); end.Before(min) {