testing: say what was the timeout if it fires

It looks reasonable here and may be useful.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/12252043

src/pkg/testing/testing.go

@@ -371,12 +371,12 @@ func Main(matchString func(pat, str string) (bool, error), tests []InternalTest,
 	haveExamples = len(examples) > 0
 	testOk := RunTests(matchString, tests)
 	exampleOk := RunExamples(matchString, examples)
+	stopAlarm()
 	if !testOk || !exampleOk {
 		fmt.Println("FAIL")
 		os.Exit(1)
 	}
 	fmt.Println("PASS")
-	stopAlarm()
 	RunBenchmarks(matchString, benchmarks)
 	after()
 }
@@ -561,7 +561,9 @@ var timer *time.Timer
 // startAlarm starts an alarm if requested.
 func startAlarm() {
 	if *timeout > 0 {
-		timer = time.AfterFunc(*timeout, alarm)
+		timer = time.AfterFunc(*timeout, func() {
+			panic(fmt.Sprintf("test timed out after %v", *timeout))
+		})
 	}
 }
 
@@ -572,11 +574,6 @@ func stopAlarm() {
 	}
 }
 
-// alarm is called if the timeout expires.
-func alarm() {
-	panic("test timed out")
-}
-
 func parseCpuList() {
 	if len(*cpuListStr) == 0 {
 		cpuList = append(cpuList, runtime.GOMAXPROCS(-1))