Question

有没有人举例说明如何在Windows 8 Metro应用程序中对异步方法进行单元测试，以确保它抛出所需的异常？

给定一个带有异步方法的类

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;
    }
}

我想使用新的Async.ExpectsException构造编写测试方法。我试过了： -

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

但当然测试不会等待异步方法完成，因此导致测试失败，但是没有抛出异常。

Answer 1

您可以对常规ExpectedExceptionAttribute使用async Task单元测试：

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

来自评论的更新 ExpectedExceptionAttribute有关Assert.ThrowsException的Win8单元测试项目has been replaced，这是很好的未记录的AFAICT。这是a good change design-wise，但我不知道为什么Win8上只支持。

好吧，假设没有async - 兼容Assert.ThrowsException（由于缺少文档，我无法判断是否一个），你可以构建一个人自己：

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 ...");
  }
}

然后使用它：

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

请注意，我的示例只是对异常类型进行精确检查;您可能也希望允许后代类型。

更新2012-11-29：打开UserVoice suggestion将其添加到Visual Studio。

Answer 2

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

使用FluentAssertions中的.ShouldThrow() nuget包适用于我

Answer 3

通过添加ThrowsExceptionAsync method，现在可以在本地覆盖此内容，而无需MSTest中的第三方或扩展方法：

await Assert.ThrowsExceptionAsync<Exception>(() => { Fail(); });

Answer 4

几天前我遇到了类似的问题，结果创造了类似于斯蒂芬上面回答的问题。它以Gist的形式提供。希望它有所帮助 - github要点有完整的代码和样本用法。

/// <summary>
/// Async Asserts use with Microsoft.VisualStudio.TestPlatform.UnitTestFramework
/// </summary>
public static class AsyncAsserts
{
    /// <summary>
    /// Verifies that an exception of type <typeparamref name="T"/> is thrown when async<paramref name="func"/> is executed.
    /// The assertion fails if no exception is thrown
    /// </summary>
    /// <typeparam name="T">The generic exception which is expected to be thrown</typeparam>
    /// <param name="func">The async Func which is expected to throw an exception</param>
    /// <returns>The task object representing the asynchronous operation.</returns>
    public static async Task<T> ThrowsException<T>(Func<Task> func) where T : Exception
    {
        return await ThrowsException<T>(func, null);
    }

    /// <summary>
    /// Verifies that an exception of type <typeparamref name="T"/> is thrown when async<paramref name="func"/> is executed.
    /// The assertion fails if no exception is thrown
    /// </summary>
    /// <typeparam name="T">The generic exception which is expected to be thrown</typeparam>
    /// <param name="func">The async Func which is expected to throw an exception</param>
    /// <param name="message">A message to display if the assertion fails. This message can be seen in the unit test results.</param>
    /// <returns>The task object representing the asynchronous operation.</returns>
    public static async Task<T> ThrowsException<T>(Func<Task> func, string message) where T : Exception
    {
        if (func == null)
        {
            throw new ArgumentNullException("func");
        }

        string failureMessage;
        try
        {
            await func();
        }
        catch (Exception exception)
        {
            if (!typeof(T).Equals(exception.GetType()))
            {
                // "Threw exception {2}, but exception {1} was expected. {0}\nException Message: {3}\nStack Trace: {4}"
                failureMessage = string.Format(
                    CultureInfo.CurrentCulture,
                    FrameworkMessages.WrongExceptionThrown,
                    message ?? string.Empty,
                    typeof(T),
                    exception.GetType().Name,
                    exception.Message,
                    exception.StackTrace);

                Fail(failureMessage);
            }
            else
            {
                return (T)exception;
            }
        }

        // "No exception thrown. {1} exception was expected. {0}"
        failureMessage = string.Format(
                    CultureInfo.CurrentCulture,
                    FrameworkMessages.NoExceptionThrown,
                    message ?? string.Empty,
                    typeof(T));

        Fail(failureMessage);
        return default(T);
    }

    private static void Fail(string message, [CallerMemberName] string assertionName = null)
    {
        string failureMessage = string.Format(
            CultureInfo.CurrentCulture,
            FrameworkMessages.AssertionFailed,
            assertionName,
            message);

        throw new AssertFailedException(failureMessage);
    }
}

Answer 5

支持在ThrowsException方法中使用异步lambda已经been added in Visual Studio 2012 Update 2，但仅适用于Windows应用商店测试项目。

唯一的问题是，您需要使用Microsoft.VisualStudio.TestPlatform.UnitTestFramework.AppContainer.Assert课程来调用ThrowsException。

因此，要使用新的ThrowsException方法，您可以执行以下操作：

using AsyncAssert = Microsoft.VisualStudio.TestPlatform.UnitTestFramework.AppContainer.Assert;

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

Answer 6

这对我有用

    public async Task TestMachineAuthBadJson() {
        // Arrange

        // act
        DocsException ex = await Assert.ThrowsExceptionAsync<DocsException>(() => MachineAuth.GetToken());
        //assert
        StringAssert.Contains(ex.Message, "DOCS-API error: ");

        }

Answer 7

这是一个老问题，但我现在偶然发现了这个问题，并决定对该问题提供更新的答案。

Xuint 现在支持使用 Assert.ThrowsAsync 方法进行异步异常测试。

Answer 8

好吧，或者只用.GetAwaiter().GetResult()来包装异常：

Assert.ThrowsException<DivideByZeroException>(() => AsyncMathsStatic.Divide(4, 0).GetAwaiter().GetResult());

针对特定异常的单元测试异步方法

8 个答案: