如何处理任务中的xUnit .NET的Assert.Throws＆LT抛出的异常; T＆GT ;? [英] How to handle exceptions thrown by Tasks in xUnit .net's Assert.Throws<T>?

问题描述

与的λ标记有异步<以下异步 xUnit.net 测试/ code>修改通过报告，没有异常被抛出失败：

The following asynchronous xUnit.net test with a lambda marked with the async modifier fails by reporting that no exception was thrown:

    [Theory, AutoWebData]
    public async Task SearchWithNullQueryThrows(
        SearchService sut,
        CancellationToken dummyToken)
    {
        // Fixture setup
        // Exercise system and verify outcome
        Assert.Throws<ArgumentNullException>(async () =>
            await sut.SearchAsync(null, dummyToken));
        // Teardown
    }

要确保一个 ArgumentNullException 实际上是扔我明确地使用了的try-catch 块。它的工作，然而所得到的code是不干净（相比于第一测试）：

To make sure that an ArgumentNullException is actually thrown I explicitly used a try-catch block. It worked, however the resulting code is not clean (compared to the first test):

[Theory, AutoWebData]
public async Task SearchWithNullQueryThrows(
    SearchService sut,
    CancellationToken dummyToken)
{
    // Fixture setup
    var expected = typeof(ArgumentNullException);
    Type actual = null;
    // Exercise system
    try
    {
        await sut.SearchAsync(null, dummyToken);
    }
    catch (ArgumentNullException e)
    {
        actual = e.GetType();
    }
    // Verify outcome
    Assert.Equal(expected, actual);
    // Teardown
}

为什么 Assert.Throws＆LT; T＆GT; 与的λ标记有异步修改失败？

推荐答案

更新

这已经解决了的xUnit 2，增加的 Assert.ThrowsAsync 。

This has been solved in xUnit 2, with the addition of Assert.ThrowsAsync.

我怀疑 Assert.Throws 未异步 -Aware。我建议提高这个问题与团队的xUnit，提示 ThrowsAsync 添加。

I am suspecting that Assert.Throws is not async-aware. I recommend raising this issue with the xUnit team, suggesting a ThrowsAsync be added.

这是异步委托在这种情况下返回工作或任务＆LT; T＆GT; 和 ArgumentNullException 不是抛出的代表直接;相反，它被放置在工作（ Task.Exception.InnerException ）。 Assert.Throws 是预期的异常直接抛出的代表，而不是放置在返回值的属性。

An async delegate in this case is returning Task or Task<T>, and the ArgumentNullException is not thrown out of the delegate directly; instead, it is placed on the Task (Task.Exception.InnerException). Assert.Throws is expecting the exception to be thrown out of the delegate directly, not placed on a property of the return value.

您可以创建自己的 AssertEx.ThrowsAsync 这样：

You can create your own AssertEx.ThrowsAsync as such:

public static async Task ThrowsAsync<TException>(Func<Task> func)
{
  var expected = typeof(TException);
  Type actual = null;
  try
  {
    await func();
  }
  catch (Exception e)
  {
    actual = e.GetType();
  }
  Assert.Equal(expected, actual);
}

其可以用作这种

[Theory, AutoWebData]
public async Task SearchWithNullQueryThrows(
    SearchService sut,
    CancellationToken dummyToken)
{
    // Fixture setup
    // Exercise system and verify outcome
    await AssertEx.ThrowsAsync<ArgumentNullException>(async () =>
        await sut.SearchAsync(null, dummyToken));
    // Teardown
}

我在使用MSTest的类似的方法。

I use a similar approach in MSTest.

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