`TestContextDecorator` never exits if `setUp` fails in tests

[Anthony King]

when using TestContextDecorator as a class decorator, enable is called just before Test.setUp, and disable is called after Test.tearDown.

unfortunately, tearDown is not called in the event of a failure inside setUp. This can result in unexpected behaviour.

Even though this class is not documented, there are decorators that use it that are.

example:

class example_decorator(TestContextDecorator):
    some_var = False

    def enable(self):
        self.__class__.some_var = True

    def disable(self):
        self.__class__.some_var = False

class Example1TestCase(TestCase):
    def test_var_is_false(self):
        # some_var will be False
        self.assertFalse(example_decorator.some_var)


@example_decorator()
class Example2TestCase(TestCase):
    def setUp(self):
        raise Exception

    def test_var_is_true(self):
        # won't be hit due to exception in setUp
        self.assertTrue(example_decorator.some_var)


class Example3TestCase(TestCase):
    def test_var_is_false(self):
        # some_var will be True now due to no cleanup in Example2TestCase
        self.assertFalse(example_decorator.some_var)

output:

.EF
======================================================================
ERROR: test_var_is_true (example.tests.Example2TestCase)
----------------------------------------------------------------------
... Traceback

======================================================================
FAIL: test_var_is_false (example.tests.Example3TestCase)
----------------------------------------------------------------------
...
AssertionError: True is not false

Ran 3 tests in 0.007s

FAILED (failures=1, errors=1)

There are 2 potential fixes here:

• decorate setUpClass and tearDownClass
• use addCleanup inside the setUp decorator

addCleanup will always run, and will only ever be registered if the context manager was successfully enabled.

It would also be useful to have this class documented, however that's out of scope of this ticket.

[Simon Charette]

Using addCleanup instead of hooking up on tearDown makes sense here.