t.Fatalf("Once.Do did not panic")
			}
		}()
		once.Do(func() {
			panic("failed")
		})
	}()

	once.Do(func() {
		t.Fatalf("Once.Do called twice")
	})
}

func BenchmarkOnce(b *testing.B) {
	var once Once
	f := func() {}
	b.RunParallel(func(pb *testing.PB) {
		for pb.Next() {
			once.Do(f)
		}
	})