c# - 尽管抛出异常，但测试 ExpectedException 的单元测试失败

Question

开始用C#实现单元测试，使用MSTest

在这个特定的测试中，我试图验证是否抛出了 ArgumentNullException。尽管我的代码确实抛出了异常，但我的测试失败了，因为它显然没有收到那种类型的异常。

我哪里错了？一定会很简单....

我的测试是这样的:

[TestMethod()]
[ExpectedException(typeof(ArgumentNullException), "A null HttpContent was inappropriately allowed")]
public void Test_HttpContent_Null_Throws_Exception()
{
    MultipartFormDataMemoryStreamProvider provider = new MultipartFormDataMemoryStreamProvider();
    Assert.ThrowsException<ArgumentNullException>(()=>provider.GetStream(null, null));
}

GetStreams() 方法如下所示:

public override Stream GetStream(HttpContent parent, HttpContentHeaders headers)
    {
        if (parent == null)
            throw new ArgumentNullException("parent");

        if (headers == null)
            throw new ArgumentNullException("headers");

        var contentDisposition = headers.ContentDisposition;
        if (contentDisposition == null)
            throw new InvalidOperationException("Did not find required 'Content-Disposition' header field in MIME multipart body part.");

        _isFormData.Add(String.IsNullOrEmpty(contentDisposition.FileName));
        return base.GetStream(parent, headers);
    }

Answer 1

这一行中的断言正在处理异常:

Assert.ThrowsException<ArgumentNullException>(()=>provider.GetStream(null, null));

因此，就 ExpectedException 而言，测试框架并未发现它被抛出。您可以删除属性或断言:

[TestMethod()]
[ExpectedException(typeof(ArgumentNullException), "A null HttpContent was inappropriately allowed")]
public void Test_HttpContent_Null_Throws_Exception()
{
    MultipartFormDataMemoryStreamProvider provider = new MultipartFormDataMemoryStreamProvider();
    provider.GetStream(null, null);
}