class TestNumbers:
    def test_numbers(self):
        assert 1 == 1

class TestSubclass(TestCase):
    def test_numbers(self):
        assert 1 == 1

class Test_underscores_and_123(TestCase):
    def test_underscores(self):
        assert 1 == 1

class TestNestedClass:
    def test_nested(self):
        class NestedClass:
            ...
        assert 1 == 1
