if err != "sync: negative WaitGroup counter" {
			t.Fatalf("Unexpected panic: %#v", err)
		}
	}()
	wg := &WaitGroup{}
	wg.Add(1)
	wg.Done()
	wg.Done()
	t.Fatal("Should panic")
}

func TestWaitGroupRace(t *testing.T) {
	// Run this test for about 1ms.
	for i := 0; i < 1000; i++ {
		wg := &WaitGroup{}
		n := new(int32)
		// spawn goroutine 1
		wg.Add(1)
		go func() {
			atomic.AddInt32(n, 1)
			wg.Done()