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Testing for Expected Exceptions with Visual Studio

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Since I seem to be on a roll blogging this morning, I thought I'd see if I could get one more in before my baby girl wakes up to have breakfast with "Da-da."

When transitioning a couple of years ago from using NUnit to Visual Studio 2005, I noticed that the ExpectedExceptionAttribute didn't quite do what I expected (no pun intended) based on my experience with NUnit.

With NUnit, you could specify the expected message text of the exception and NUnit would transparently perform an assertion on the actual message. In Visual Studio 2005, I found the following "pattern" useful for mimicking the familiar behavior of NUnit:

 [TestMethod()]
[ExpectedException(typeof(ArgumentException))]
public void FindByWhidWithInvalidWhid()
{
    const string expectedExceptionMessage = "A valid WHID must be specified.\r\nParameter name: whid";

    string project1Url = Properties.Settings.Default.Project1Url;

    SPSite site = new SPSite(project1Url);

    try
    {
        PrimaryDocumentService.FindByWhid(site, 0);
    }
    catch (ArgumentException ex)
    {
        Assert.AreEqual(expectedExceptionMessage, ex.Message);
        throw;
    }
}

The internal try/catch block validates the expected message, whereas the ExpectedException attribute on the method delegates the remaining work to the Visual Studio test manager (i.e. showing green vs. red for each test).

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