testing: in TestRacyOutput, ensure that the Run calls complete before cleanup

Also tweak the failure message added in CL 352349.

Updates #18741.
Updates #48515.

Change-Id: I46ed84c6f498d7a68414cc3dab3c1cd55da69aa9
Reviewed-on: https://go-review.googlesource.com/c/go/+/451215
Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Changkun Ou <mail@changkun.de>
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/testing/panic_test.go

@@ -227,7 +227,7 @@ func TestMorePanic(t *testing.T) {
 		{
 			desc:  "Issue 48515: call t.Run in t.Cleanup should trigger panic",
 			flags: []string{"-test.run=TestCallRunInCleanupHelper"},
-			want:  `panic: testing: t.Run is called during t.Cleanup`,
+			want:  `panic: testing: t.Run called during t.Cleanup`,
 		},
 	}
 

src/testing/sub_test.go

@@ -805,13 +805,13 @@ func TestRacyOutput(t *T) {
 		return len(b), nil
 	}
 
-	var wg sync.WaitGroup
 	root := &T{
 		common:  common{w: &funcWriter{raceDetector}},
 		context: newTestContext(1, allMatcher()),
 	}
 	root.chatty = newChattyPrinter(root.w)
 	root.Run("", func(t *T) {
+		var wg sync.WaitGroup
 		for i := 0; i < 100; i++ {
 			wg.Add(1)
 			go func(i int) {
@@ -821,8 +821,8 @@ func TestRacyOutput(t *T) {
 				})
 			}(i)
 		}
+		wg.Wait()
 	})
-	wg.Wait()
 
 	if races > 0 {
 		t.Errorf("detected %d racy Writes", races)

src/testing/testing.go

@@ -1588,7 +1588,7 @@ func tRunner(t *T, fn func(t *T)) {
 // must return before the outer test function for t returns.
 func (t *T) Run(name string, f func(t *T)) bool {
 	if t.cleanupStarted.Load() {
-		panic("testing: t.Run is called during t.Cleanup")
+		panic("testing: t.Run called during t.Cleanup")
 	}
 
 	t.hasSub.Store(true)