unittest subTests() fails when called from debug()

[nicoddemus]

BPO	34900
Nosy	@berkerpeksag, @nicoddemus, @tirkarthi
PRs	bpo-34900: Fix subTests to not crash when called from TestCase.debug() #9707 [3.7] bpo-34900: Make TestCase.debug() work with subtests (GH-9707) #9818 [3.6] bpo-34900: Make TestCase.debug() work with subtests (GH-9707) #9819

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2018-10-12.11:09:21.672>
created_at = <Date 2018-10-04.22:24:33.818>
labels = ['3.7', '3.8', 'type-bug', 'library']
title = 'unittest subTests() fails when called from debug()'
updated_at = <Date 2018-10-12.11:09:21.672>
user = 'https://github.com/nicoddemus'

bugs.python.org fields:

activity = <Date 2018-10-12.11:09:21.672>
actor = 'berker.peksag'
assignee = 'none'
closed = True
closed_date = <Date 2018-10-12.11:09:21.672>
closer = 'berker.peksag'
components = ['Library (Lib)']
creation = <Date 2018-10-04.22:24:33.818>
creator = 'Bruno Oliveira'
dependencies = []
files = []
hgrepos = []
issue_num = 34900
keywords = ['patch']
message_count = 8.0
messages = ['327092', '327115', '327117', '327121', '327123', '327577', '327579', '327580']
nosy_count = 3.0
nosy_names = ['berker.peksag', 'Bruno Oliveira', 'xtreak']
pr_nums = ['9707', '9818', '9819']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue34900'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

[nicoddemus]

Consider this code:

    import unittest


    class TC(unittest.TestCase):

        def test_subtest(self):
            with self.subTest():
                pass


    tc = TC('test_subtest')
    tc.run()

This works when executed, but if we change tc.run() to tc.debug() we get the following exception:

    Traceback (most recent call last):
      File ".tmp\test-unittest-regression.py", line 13, in <module>
        tc.debug()
      File "C:\Users\Bruno\AppData\Local\Programs\Python\Python36\lib\unittest\case.py", line 658, in debug
        getattr(self, self._testMethodName)()
      File ".tmp\test-unittest-regression.py", line 7, in test_subtest
        with self.subTest():
      File "C:\Users\Bruno\AppData\Local\Programs\Python\Python36\lib\contextlib.py", line 81, in __enter__
        return next(self.gen)
      File "C:\Users\Bruno\AppData\Local\Programs\Python\Python36\lib\unittest\case.py", line 512, in subTest
        if not self._outcome.result_supports_subtests:
    AttributeError: 'NoneType' object has no attribute 'result_supports_subtests'    

Looking at the code, subTest assumes that the TestCase instance has the self._outcome atribute, which is set only by run().

[berkerpeksag]

PR 9707 looks good to me. I will merge it once your CLA is processed by the PSF staff. Thanks!

[nicoddemus]

Great, thanks again for the quick review.

[berkerpeksag]

FYI, I just noticed that this is a duplicate of bpo-29551, but decided to keep this one open.

[nicoddemus]

FYI, I just noticed that this is a duplicate of bpo-29551, but decided to keep this one open.

OK thanks. I did try to search for open issues before filing this one by using the "subtest result_supports_subtests" terms, as I figured a bug report would include the traceback, that's why I didn't find 29551, heh.

[berkerpeksag]

New changeset da2bf9f by Berker Peksag (Bruno Oliveira) in branch 'master':
bpo-34900: Make TestCase.debug() work with subtests (GH-9707)
da2bf9f

[berkerpeksag]

New changeset 7a98e30 by Berker Peksag (Miss Islington (bot)) in branch '3.7':
bpo-34900: Make TestCase.debug() work with subtests (GH-9707)
7a98e30

[berkerpeksag]

New changeset c1fe49c by Berker Peksag (Miss Islington (bot)) in branch '3.6':
bpo-34900: Make TestCase.debug() work with subtests (GH-9707)
c1fe49c