验证暂停功能在模拟一段时间后尚未返回值

Question

我试图验证悬挂功能在一定的测试中根本不会返回任何内容。

考虑以下情况：

val completionSignal = Channel<Unit>(capacity = 1, onBufferOverflow = BufferOverflow.DROP_LATEST)

suspend fun waitForCompletionSignal(): String {
  completionSignal.receive()
  return "Completion signal received"
}

我想通过2个单元测试测试此代码，一个验证它在我提供一个值的完成时返回字符串（这很容易）。 当我不给任何东西时，它验证它不会返回任何东西的一个。这是很难的，因为我应该等多长时间？如果我的代码更改并突然返回字符串，我可以确保测试失败吗？

我得到了以下方法，但我缺少一些文章：

@Test
fun `waitForCompletionSignal when completionSignal is provided assert result`() = runTest {
  // Start waiting for result
  val result = async { waitForCompletionSignal() }
  // Provide completion signal
  completionSignal.trySend(Unit)

  // Await result and verify its correct
  assertThat(result.await() == "Completion signal received")
}

@Test
fun `waitForCompletionSignal when completionSignal is not provided assert no result`() = runTest {
  // Start waiting for result
  val result = async { waitForCompletionSignal() }

  // TODO?? some validation that succeeds if the test is just like this, but fails when i do the following:
  completionSignal.trySend(Unit)
  // A regular await would wait indefinately, and checking if the deferred result is completed does not work very well as well.
}

我希望这个问题很明确，谢谢。

Answer 1

我在延期类型上制作了扩展功能，以便能够等待最大的时间，然后它将返回null。在我的特殊情况下，延迟时间为0（因此，任何延迟）就足够了，但是我可以想象，在某些情况下，它有助于延迟最少的时间。

@ExperimentalCoroutinesApi
suspend inline fun <reified T> Deferred<T>.awaitOrNull(
    time: Long = 0,
    crossinline actBlock: () -> Unit = { }
): T? = coroutineScope {
    actBlock()

    val timeoutJob = async<T?> {
        delay(time)
        null
    }

    return@coroutineScope select<T?> {
        [email protected] {
            timeoutJob.cancel()
            it
        }
        timeoutJob.onAwait {
            [email protected]()
            it
        }
    }
}

使用此方法，我可以按照预期编写以下未能失败 /成功的测试：

// Succeeds
@Test
fun `waitForCompletionSignal when completionSignal is provided assert result`() = runTest {
  val result = async { 
    waitForCompletionSignal()
  }.awaitOrNull {
    completionSignal.trySend(Unit)
  }

  assertThat(result == "Completion signal received")
}

// Succeeds
@Test
fun `waitForCompletionSignal when completionSignal is not provided assert no result`() = runTest {
  val result = async { 
    waitForCompletionSignal()
  }.awaitOrNull()

  assertThat(result == null)
}

// Fails (to prove that it works)
@Test
fun `waitForCompletionSignal when completionSignal is not provided assert no result`() = runTest {
  val result = async { 
    waitForCompletionSignal()
  }.awaitOrNull {
    completionSignal.trySend(Unit) // This (obviously) causes the test to fail, as I wanted.
  }

  assertThat(result == null)
}