对于特定的异常单元测试异步方法 [英] Unit testing async method for specific exception

问题描述

有没有人有在Windows 8 Metro应用如何单元测试一个异步方法的例子，以确保它抛出所需的例外呢？

Does anyone have an example of how to unit test an async method in a Windows 8 Metro application, to ensure that it throws the required exception?

给定一个类与异步方法

public static class AsyncMathsStatic
{
    private const int DELAY = 500;

    public static async Task<int> Divide(int A, int B)
    {
        await Task.Delay(DELAY);
        if (B == 0)
            throw new DivideByZeroException();
        else
            return A / B;
    }
}

我想写使用新的异步测试方法.ExpectsException建设。我试过： -

I want to write a test method using the new Async.ExpectsException construction. I've tried :-

[TestMethod]
public void DivideTest1()
{
    Assert.ThrowsException<DivideByZeroException>(async () => { int Result = await AsyncMathsStatic.Divide(4, 0); });
}

但当然的测试不等待异步方法来完成，所以导致失败的测试该异常没有抛出。

but of course the test doesn't wait for the async method to complete, and so results in a failed test that the exception hasn't been thrown.

推荐答案

您可以使用异步任务与常规 <单元测试code> ExpectedExceptionAttribute ：

You can use an async Task unit test with the regular ExpectedExceptionAttribute:

[TestMethod]
[ExpectedException(typeof(DivideByZeroException))]
public async Task DivideTest1()
{
  int Result = await AsyncMathsStatic.Divide(4, 0);
}

从评论更新： ExpectedExceptionAttribute 上Win8的单元测试项目的已取代与 Assert.ThrowsException ，这是很好的无证AFAICT。这是个不错的改变设计明智的，但我不知道为什么它的只有的支持Win8的

Update from comment: ExpectedExceptionAttribute on Win8 unit test projects has been replaced with Assert.ThrowsException, which is nicely undocumented AFAICT. This is a good change design-wise, but I don't know why it's only supported on Win8.

那么，假设没有异步 - 兼容 Assert.ThrowsException （我不能，如果有讲的是的一个或不是由于缺少文件），你可以自己定义：

Well, assuming that there's no async-compatible Assert.ThrowsException (I can't tell if there is one or not due to lack of documentation), you could build one yourself:

public static class AssertEx
{
  public async Task ThrowsExceptionAsync<TException>(Func<Task> code)
  {
    try
    {
      await code();
    }
    catch (Exception ex)
    {
      if (ex.GetType() == typeof(TException))
        return;
      throw new AssertFailedException("Incorrect type; expected ... got ...", ex);
    }

    throw new AssertFailedException("Did not see expected exception ...");
  }
}

，然后用它作为这样的：

and then use it as such:

[TestMethod]
public async Task DivideTest1()
{
  await AssertEx.ThrowsException<DivideByZeroException>(async () => { 
      int Result = await AsyncMathsStatic.Divide(4, 0);
  });
}

请注意，这里我举的例子只是做了异常类型的精确检查;你可能更愿意让后人类型以及

Note that my example here is just doing an exact check for the exception type; you may prefer to allow descendant types as well.

更新2012年11月29日：开了的UserVoice建议把它添加到Visual Studio。

Update 2012-11-29: Opened a UserVoice suggestion to add this to Visual Studio.

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