I use the standard unittest module for testing, despite the community’s general protestations about it not being pythonic. It does what I need, except for one thing. It has an assertRaises method that tests that a callable raises an exception of the expected class, but the message that comes with the exception is not checked. So I usually mix this method into my test case base class:

def assertRaisesMsg(self, excClass, msg, callableObj, *args, **kwargs):
    """ Just like unittest.TestCase.assertRaises,
        but checks that the message is right too.
    """
    try:
        callableObj(*args, **kwargs)
    except excClass, exc:
        excMsg = str(exc)
        if not msg:
            # No message provided: any message is fine.
            return
        elif excMsg == msg:
            # Message provided, and we got the right message: it passes.
            return
        else:
            # Message provided, and it didn't match: fail!
            raise self.failureException(
                "Right exception, wrong message: got '%s' expected '%s'" % 
                (excMsg, msg)
                )
    else:
        if hasattr(excClass, '__name__'):
            excName = excClass.__name__
        else:
            excName = str(excClass)
        raise self.failureException(
            "Expected to raise %s, didn't get an exception at all" % 
            excName
            )

I can call it (for example) like this:

self.assertRaisesMsg(MyException, "Exception message", my_function, (arg1, arg2))

This test line will call my_function(arg1, arg2) and succeed if it raises a MyException with the message “Exception message”. It will fail in all other cases.