NUnit的异步测试例外断言

Question

我有一个控制器UserController这个动作

// GET /blah 
public Task<User> Get(string domainUserName) 
{ 
     if (string.IsNullOrEmpty(domainUserName)) 
     { 
      throw new ArgumentException("No username specified."); 
     } 

     return Task.Factory.StartNew(
      () => 
       { 
        var user = userRepository.GetByUserName(domainUserName); 
        if (user != null) 
        { 
         return user; 
        } 

        throw new HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.NotFound, string.Format("{0} - username does not exist", domainUserName))); 
       }); 
} 

我想写的，我抛出一个异常404的情况下进行测试。

这是我曾尝试与输出 -

1）

[Test] 
public void someTest() 
{ 
     var mockUserRepository = new Mock<IUserRepository>(); 
     mockUserRepository.Setup(x => x.GetByUserName(It.IsAny<string>())).Returns(default(User)); 
    var userController = new UserController(mockUserRepository.Object) { Request = new HttpRequestMessage() }; 

    Assert.That(async() => await userController.Get("foo"), Throws.InstanceOf<HttpResponseException>()); 
} 

结果 测试失败

Expected: instance of <System.Web.Http.HttpResponseException> 
    But was: no exception thrown 

2）

[Test] 
public void someTest() 
{ 
     var mockUserRepository = new Mock<IUserRepository>(); 
     mockUserRepository.Setup(x => x.GetByUserName(It.IsAny<string>())).Returns(default(User)); 
    var userController = new UserController(mockUserRepository.Object) { Request = new HttpRequestMessage() }; 

    var httpResponseException = Assert.Throws<HttpResponseException>(() => userController.Get("foo").Wait()); 
    Assert.That(httpResponseException.Response.StatusCode, Is.EqualTo(HttpStatusCode.NotFound)); 
} 

结果 测试失败

Expected: <System.Web.Http.HttpResponseException> 
    But was: <System.AggregateException> (One or more errors occurred.) 

3）

[Test] 
public void someTest() 
{ 
     var mockUserRepository = new Mock<IUserRepository>(); 
     mockUserRepository.Setup(x => x.GetByUserName(It.IsAny<string>())).Returns(default(User)); 
    var userController = new UserController(mockUserRepository.Object) { Request = new HttpRequestMessage() }; 

    var httpResponseException = Assert.Throws<HttpResponseException>(async() => await userController.Get("foo")); 
    Assert.That(httpResponseException.Response.StatusCode, Is.EqualTo(HttpStatusCode.NotFound)); 
} 

结果 测试失败

Expected: <System.Web.Http.HttpResponseException> 
    But was: null 

4）

[Test] 
[ExpectedException(typeof(HttpResponseException))] 
public async void ShouldThrow404WhenNotFound() 
{   var mockUserRepository = new Mock<IUserRepository>(); 
     mockUserRepository.Setup(x => x.GetByUserName(It.IsAny<string>())).Returns(default(User)); 

    var userController = new UserController(mockUserRepository.Object) { Request = new HttpRequestMessage() }; 

    var task = await userController.Get("foo"); 
} 

结果 测试通过

问题 -

1. 为什么Assert.Throws不能处理HttpResponseException时的ExpectedException呢？
2. 我不想仅仅测试引发的异常。我想在响应的状态代码上声明。有什么办法做到这一点？

对这些行为及其原因的任何比较都会很棒！

Answer 1

你所看到的问题，是由于async void。

特别是：

1）async() => await userController.Get("foo")被转换成TestDelegate，它返回void，所以你lambda表达式作为async void处理。所以测试运行者将开始执行lambda，但不会等待它完成。在Get完成之前，lambda返回（因为它是async），并且测试运行程序发现它没有异常返回。

2）Wait在AggregateException中包含任何例外。

3）同样，async lambda被视为async void，所以测试运行者不会等待其完成。

4）我建议你制作async Task而不是async void，但在这种情况下，测试运行器会等待完成，从而发现异常。

根据this bug report，在NUnit的下一个版本中会有一个修复。同时，您可以建立自己的ThrowsAsync方法;一个example for xUnit is here。

Answer 2

如果您等待任务，则引发的异常将聚合到AggregateException中。您可以检查AggregateException的内部异常。这可能是你案例2不起作用的原因。

在任务中运行的用户代码抛出的未处理的异常会传播回加入的线程，本主题后面介绍的某些情况除外。当您使用静态或实例Task.Wait或Task.Wait方法之一时会传播异常，并通过将该调用放入try-catch语句中来处理它们。如果任务是附加的子任务的父级，或者您正在等待多个任务，则可能会抛出多个异常。为了将所有异常传播回调用线程，Task基础结构将它们包装在一个AggregateException实例中。 AggregateException有一个InnerExceptions属性，可以通过枚举来检查所有引发的原始异常，并分别处理（或不处理）每个异常。即使只抛出一个异常，它仍然包装在一个AggregateException中。

Link to MSDN

Answer 3

This blog约与我相似的问题举行了会谈。

我跟着那里提出的建议，并有一个这样的试验 -

[Test] 
    public void ShouldThrow404WhenNotFound() 
    { 
     var mockUserRepository = new Mock<IUserRepository>(); 
     mockUserRepository.Setup(x => x.GetByUserName(It.IsAny<string>())).Returns(default(User)); 
     var userController = new UserController(mockUserRepository.Object) { Request = new HttpRequestMessage() }; 

     var aggregateException = Assert.Throws<AggregateException>(() => userController.Get("foo").Wait()); 
     var httpResponseException = aggregateException.InnerExceptions 
      .FirstOrDefault(x => x.GetType() == typeof(HttpResponseException)) as HttpResponseException; 

     Assert.That(httpResponseException, Is.Not.Null); 
     Assert.That(httpResponseException.Response.StatusCode, Is.EqualTo(HttpStatusCode.NotFound)); 
    } 

我不太高兴，但是，这个工作。

编辑1

通过@StephenCleary的启发，我添加了一个静态辅助的类，它的断言，我期待的。它看起来像这样 -

public static class AssertEx 
{ 
    public static async Task ThrowsAsync<TException>(Func<Task> func) where TException : class 
    { 
     await ThrowsAsync<TException>(func, exception => { }); 
    } 

    public static async Task ThrowsAsync<TException>(Func<Task> func, Action<TException> action) where TException : class 
    { 
     var exception = default(TException); 
     var expected = typeof(TException); 
     Type actual = null; 
     try 
     { 
      await func(); 
     } 
     catch (Exception e) 
     { 
      exception = e as TException; 
      actual = e.GetType(); 
     } 

     Assert.AreEqual(expected, actual); 
     action(exception); 
    } 
} 

我现在能有这样一个试验 -

[Test] 
    public async void ShouldThrow404WhenNotFound() 
    { 
     var mockUserRepository = new Mock<IUserRepository>(); 
     mockUserRepository.Setup(x => x.GetByUserName(It.IsAny<string>())).Returns(default(User)); 
     var userController = new UserController(mockUserRepository.Object) { Request = new HttpRequestMessage() }; 

     Action<HttpResponseException> asserts = exception => Assert.That(exception.Response.StatusCode, Is.EqualTo(HttpStatusCode.NotFound)); 
     await AssertEx.ThrowsAsync(() => userController.Get("foo"), asserts); 
    } 

Answer 4

我不知道的时候加入，但的NUnit（3.4.1在写作时）的最新版本包括ThrowsAsync方法

看到https://github.com/nunit/docs/wiki/Assert.ThrowsAsync

我没有测试过这个例子具体而言，但它应该像这样工作：

[Test] 
public async void ShouldThrow404WhenNotFound() 
{ 
    var mockUserRepository = new Mock<IUserRepository>(); 
    mockUserRepository.Setup(x => x.GetByUserName(It.IsAny<string>())).Returns(default(User)); 
    var userController = new UserController(mockUserRepository.Object) { Request = new HttpRequestMessage() }; 

    var exception = Assert.ThrowsAsync<HttpResponseException>(() => userController.Get("foo")); 

    Assert.That(exception.Response.StatusCode, Is.EqualTo(HttpStatusCode.NotFound)); 
}