Is there any way how to test contracts set using Code contracts?

I would like to write unit test that verify that my method does not accept invalid arguments. Validity of arguments is checked using Code Contract's Contract.Requires call. Why would I want to test contracts? I consider my tests to be kind of method specification (that is actually idea taken from TDD) so by testing that the method fails for some arguments I specify that such arguments should not be used.

The problem is that since I started to use Code contracts I cannot test method contracts because I cannot access the exception that is thrown by Contract.Requires. I can catch generic Exception but that just is not nice... Is there recommended/supported way how to test contract set using Code Contracts?

Seems to me that Code Contracts does not really support unit testing...

EDIT: My test example (I am forced to catch generic exception)

[ExpectedException(typeof(Exception), AllowDerivedTypes = true)]
public void Compute_Throws_ForNullArgument()
{
    new ComputingService().Compute(null);
}
Jon Skeet
people
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You can't explicitly catch the right exception type, but you could catch Exception and then check that it's a ContractException using reflection (rethrowing otherwise).

That would be ugly to do everywhere, but you just need to do it once:

public static void AssertContractFailure(Action action)
{
    try
    {
        action();
        Assert.Fail("Expected contract violation");
    }
    catch (Exception e)
    {
        if (...) // I can't remember offhand what you'd need to check
        {
            throw;
        }
    }
}

Then:

AssertContractFailure(() => SomeContractViolation(...));

Currently if you have that in a helper class you'd need to qualify the call everywhere, but as of C# 6 you'll hopefully be able to import it easily :)

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