虽然抛出异常，但测试ExpectedException的单元测试失败

Question

Starting to implement unit tests in C#, using MSTest

In this particular test I am trying to verify that an ArgumentNullException is being thrown. Even though my code does throw the exception my test is failing because it apparently did not receive that type of exception.

Where am I going wrong? Bound to be something simple....

My test looks like this:

[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));
}

And the GetStreams() method looks like this:

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

The assert in this line is handling the exception:

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

So the testing framework isn't seeing it being thrown as far as ExpectedException is concerned. You can either remove the attribute, or the assert:

[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);
}