Python - test that succeeds when exception is not

Question

I know about unittest Python module.

I know about assertRaises() method of TestCase class.

I would like to write a test that succeeds when an exception is not raised.

Any hints please?

Answer 1

I use this pattern for the kind of assertion you've asked:

with self.assertRaises(Exception):
    try:
        doStuff()
    except:
        pass
    else:
        raise Exception

It will fail exactly when exception is raised by doStuff().

Answer 2

def runTest(self):
    try:
        doStuff()
    except:
        self.fail("Encountered an unexpected exception.")

UPDATE: As liw.fi mentions, the default result is a success, so the example above is something of an antipattern. You should probably only use it if you want to do something special before failing. You should also catch the most specific exceptions possible.

Answer 3

The test runner will catch all exceptions you didn't assert would be raised. Thus:

doStuff()
self.assert_(True)

This should work fine. You can leave out the self.assert_ call, since it doesn't really do anything. I like to put it there to document that I didn't forget an assertion.