Regression: unittest.TestCase.tearDown executed on skipped tests under --pdb

[rowan-stein]

User Report

When running pytest with --pdb, unittest.TestCase.tearDown is executed for skipped tests, causing errors. In pytest==5.4.1, skipped tests remained skipped under --pdb, but in pytest==5.4.2, teardown runs and raises.

Minimal test:

import unittest

class MyTestCase(unittest.TestCase):
    def setUp(self):
        xxx
    @unittest.skip("hello")
    def test_one(self):
        pass
    def tearDown(self):
        xxx

Environment:

$ python --version
Python 3.6.10
$ pip freeze
attrs==19.3.0
importlib-metadata==1.6.0
more-itertools==8.2.0
packaging==20.3
pluggy==0.13.1
py==1.8.1
pyparsing==2.4.7
pytest==5.4.2
six==1.14.0
wcwidth==0.1.9
zipp==3.1.0

Behavior without --pdb:

$ pytest test_repro.py 
============================= test session starts ==============================
platform linux -- Python 3.6.10, pytest-5.4.2, py-1.8.1, pluggy-0.13.1
rootdir: /srv/slapgrid/slappart3/srv/runner/project/repro_pytest
collected 1 item                                          

test_repro.py s                                    [100%]

============================== 1 skipped in 0.02s ==============================

Behavior with --pdb (unexpected teardown execution):

$ pytest --pdb test_repro.py 
============================= test session starts ==============================
platform linux -- Python 3.6.10, pytest-5.4.2, py-1.8.1, pluggy-0.13.1
rootdir: /srv/slapgrid/slappart3/srv/runner/project/repro_pytest
collected 1 item                                          

test_repro.py sE
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> traceback >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

self = <test_repro.MyTestCase testMethod=test_one>

    def tearDown(self):
>       xxx
E       NameError: name 'xxx' is not defined

test_repro.py:10: NameError
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> entering PDB >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

>>>>>>>>>>>>>>>>>> PDB post_mortem (IO-capturing turned off) >>>>>>>>>>>>>>>>>>
*** NameError: name 'execfile' is not defined
> /srv/slapgrid/slappart3/srv/runner/project/repro_pytest/test_repro.py(10)tearDown()
-> xxx
(Pdb) q

=========================== short test summary info ============================
ERROR test_repro.py::MyTestCase::test_one - NameError: name 'xxx' is not defined
!!!!!!!!!!!!!!!!!!! _pytest.outcomes.Exit: Quitting debugger !!!!!!!!!!!!!!!!!!!
========================= 1 skipped, 1 error in 1.83s ==========================

This appears to be a regression introduced between 5.4.1 and 5.4.2 (likely related to changes in pdb/skip/teardown logic, see PR pytest-dev#7151).

---

Researcher Specification (Emerson Gray)

Root cause:

• In src/_pytest/unittest.py, when --pdb is active, TestCaseFunction.runtest defers unittest.TestCase.tearDown by capturing the original into self._explicit_tearDown and monkeypatching tearDown to a no-op to preserve object state for debugging.
• TestCaseFunction.teardown then unconditionally calls self._explicit_tearDown() if set.
• For skipped tests (via @unittest.skip or raising unittest.SkipTest), TestCaseFunction.addSkip maps this to pytest.skip() and sets a skip tracking key (skipped_by_mark_key) in self._store.
• However, teardown does not check skip state; thus, even when skipped, deferred tearDown is invoked under --pdb.

Proposed fix (minimal and correct):

• Modify src/_pytest/unittest.py in TestCaseFunction.teardown to guard the invocation of deferred tearDown based on skip state.
• Pseudocode:

if self._explicit_tearDown is not None:
    # Only call tearDown if the test was not skipped
    if not self._store.get(skipped_by_mark_key, False):
        self._explicit_tearDown()
    self._explicit_tearDown = None

• Uses existing skipped_by_mark_key set by unittest skip handling and pytest marks; preserves behavior for non-skipped tests under --pdb.

Tests to add:

• testing/test_unittest.py::test_unittest_skip_method_does_not_call_teardown_with_pdb
  • A unittest.TestCase with @unittest.skip on a method and tearDown that would raise if called; run with --pdb; assert skipped and no teardown error.
• testing/test_unittest.py::test_unittest_setUp_raises_SkipTest_does_not_call_teardown_with_pdb
  • setUp raises unittest.SkipTest; tearDown raises if called; run with --pdb; assert skipped.
• testing/test_unittest.py::test_unittest_class_skip_does_not_call_teardown_with_pdb
  • Class-level @unittest.skip; tearDown raises if called; assert skipped under --pdb.

Edge cases & interactions:

• Pytest skip marks: unaffected (runtest not executed, no deferred teardown).
• xfail: unchanged (run=False skips in setup; expectedFailure still runs and calls teardown).
• PDB post-mortem on failures: unchanged; still enters pdb and calls teardown afterward for non-skipped tests.

We will implement this fix and add the tests, targeting the branch pytest-dev__pytest-7236.