unit testing for ArgumentNullException by param name

Question

I have a unit test and am checking for null exceptions of my controller constructor for a few different services.

[TestMethod]
[ExpectedException(typeof(ArgumentNullException))]

In my controller constructor I have:

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

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

I have a unit test for each, but how can I distinguish between the two. I can leave the test as is as either of the checks could be throwing null so I want to test the exception by param name.

Is this possible?

Answer 1

You could explicitly catch the exception in your test and then assert the value of the ParamName property:

try
{
    //test action
}
catch(ArgumentException ex)
{
    Assert.AreEqual(expectedParameterName, ex.ParamName);
}