Ignore unittests that depend on success of other tests

Question

When writing unit tests, it often happens that some tests sort of "depend" on other tests.

For example, lets suppose I have a test that checks I can instantiate a class. I have other tests that go right ahead and instantiate it and then test other functionality.

Lets also suppose that the class fails to instantiate, for whatever reason.

This results in a ton of tests giving errors. This is bad, because I can't see where the problem really is. What I need is a way of skipping these tests if my instantiation test has failed.

Is there a way of doing this with Python's unittest module?

If this isn't what I should do, what should I do so as to see where the problem really is when something breaks?

Answer 1

Actually, contrary to my comment above, I think what you need is a setUpClass method. From the docs,

If an exception is raised during a setUpClass then the tests in the class are not run and the tearDownClass is not run. [...] If the exception is a SkipTest exception then the class will be reported as having been skipped instead of as an error.

So something like this should work (I'm sure it could be neater):

class TestMyClass(unittest.TestCase):
    @classmethod
    def setUpClass(cls):
        # run the constructor test
        if constructor_test_failed:
            raise unittest.SkipTest("Constructor failed")

    def test_other_stuff(self):
        # will get run after setUpClass if it succeeded