Function WhileTestRunningLogger

tstest/log.go:153–196

WhileTestRunningLogger returns a logger.Logf that logs to t.Logf until the test finishes, at which point it no longer logs anything.

(t testenv.TB)

// WhileTestRunningLogger returns a logger.Logf that logs to t.Logf until the
// test finishes, at which point it no longer logs anything.
func WhileTestRunningLogger(t testenv.TB) logger.Logf {
	var (
		mu   sync.RWMutex
		done bool
	)
	tlogf := logger.TestLogger(t)
	logger := func(format string, args ...any) {
		t.Helper()

		mu.RLock()
		defer mu.RUnlock()

		if done {
			return
		}
		tlogf(format, args...)
	}

	// t.Cleanup is run before the test is marked as done, so by acquiring
	// the mutex and then disabling logs, we know that all existing log
	// functions have completed, and that no future calls to the logger
	// will log something.
	//
	// We can't do this with an atomic bool, since it's possible to
	// observe the following race:
	//
	//    test goroutine                goroutine 1
	//    --------------                -----------
	//                                  check atomic, testFinished = no
	//    test finishes
	//    run t.Cleanups
	//    set testFinished = true
	//                                  call t.Logf
	//                                  panic
	//
	// Using a mutex ensures that all actions in goroutine 1 in the
	// sequence above occur atomically, and thus should not panic.
	t.Cleanup(func() {
		mu.Lock()
		defer mu.Unlock()
		done = true
	})
	return logger
}