test_example.py

# frobnicator.py

class Frobnicate(object):
    def gurgle(self):
        ...

    def bargle(self):
        ...

# test_frobnicator.py

class FrobnicateTestCase(TestCase):
    def setUp(self):
        self.frob = Frobnicate()


class TestGurgle(FrobnicateTestCase):
    def test_should_gurgle_loudly(self):
        ...

    def test_should_fail_without_water(self):
        ...


class TestBargle(FrobnicateTestCase):
    def test_should_bargle_happily(self):
        ...

    def test_should_bargle_sadly_on_error(self):
        ...