Check that we can serialize the warning detail attr

[aadamson]

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I was running into the same issue addressed in #349, except instead of failing to serialize an arg of the warning, I was unable to serialize a warning detail of the warning. To reproduce the error, you can cause a ResourceWarning due to an unclosed socket. One of the warning details will be the socket that wasn't closed, which can't be serialized.

This PR addresses the issue by performing the same check as #349.

[nicoddemus]

Thanks a lot @aadamson!

---

sigh oh boy do I regret having the idea of transferring warning instances between master and workers.

[nicoddemus]

LGTM, but can you please provide a regression test for this?

See

pytest-xdist/testing/acceptance_test.py

Line 759 in f206187

def test_unserializable_arguments(self, testdir, n):

for an example that you can base a new test on.

[aadamson]

@nicoddemus My pleasure! I think it's a really cool feature :)

I'll add that test now

[nicoddemus]

Awesome, thanks!

[aadamson]

Do you guys have a guide on running the tests locally?

[nicoddemus]

Take a look at pytest's guide it is the same for pytest-xdist (we use tox to run the tests).

Please let us know if you run into trouble. 👍

[aadamson]

@nicoddemus picking this back up - I can't repro the issue (or rather, I can't figure out how to construct a test that will replicate the failure, so I can't check if the failure is handled properly). Would you be okay if I only address testing the feature in Python 3 in this PR?

[nicoddemus]

Would you be okay if I only address testing the feature in Python 3 in this PR?

Go ahead, we can try to help out to reproduce on Python 2. 👍

[aadamson]

I'm seeing TestWarnings.test_warnings fail in CI with

____________________ TestWarnings.test_warnings[pytest--n0] ____________________
self = <acceptance_test.TestWarnings instance at 0x7f51f5a4bcb0>
testdir = <Testdir local('/tmp/pytest-of-travis/pytest-0/test_warnings0')>
n = '-n0', warn_type = 'pytest'
    @pytest.mark.parametrize("n", ["-n0", "-n1"])
    @pytest.mark.parametrize("warn_type", ["pytest", "builtin"])
    def test_warnings(self, testdir, n, warn_type):
        if warn_type == "builtin":
            warn_code = """warnings.warn(UserWarning('this is a warning'))"""
        elif warn_type == "pytest":
            warn_code = """request.config.warn('', 'this is a warning',
                           fslocation=py.path.local())"""
        else:
            assert False
        testdir.makepyfile(
            """
            import warnings, py, pytest
    
            @pytest.mark.filterwarnings('ignore:config.warn has been deprecated')
            def test_func(request):
                {warn_code}
        """.format(
                warn_code=warn_code
            )
        )
        result = testdir.runpytest(n)
>       result.stdout.fnmatch_lines(["*this is a warning*", "*1 passed, 1 warnings*"])
E       Failed: nomatch: '*this is a warning*'
E           and: u'============================= test session starts =============================='
E           and: u'platform linux2 -- Python 2.7.14, pytest-4.1.0, py-1.7.0, pluggy-0.8.0'
E           and: u'rootdir: /tmp/pytest-of-travis/pytest-0/test_warnings0, inifile:'
E           and: u'plugins: xdist-1.25.1.dev6+g08c2387, forked-0.2'
E           and: u'collected 1 item'
E           and: u''
E           and: u'test_warnings.py F                                                       [100%]'
E           and: u''
E           and: u'=================================== FAILURES ==================================='
E           and: u'__________________________________ test_func ___________________________________'
E           and: u''
E           and: u'request = <FixtureRequest for <Function test_func>>'
E           and: u''
E           and: u"    @pytest.mark.filterwarnings('ignore:config.warn has been deprecated')"
E           and: u'    def test_func(request):'
E       fnmatch: '*this is a warning*'
E          with: u">       request.config.warn('', 'this is a warning',"
E       nomatch: '*1 passed, 1 warnings*'
E           and: u'                   fslocation=py.path.local())'
E           and: u"E       AttributeError: 'Config' object has no attribute 'warn'"
E           and: u''
E           and: u'test_warnings.py:5: AttributeError'
E           and: u'=========================== 1 failed in 0.01 seconds ==========================='
E           and: u''
E       remains unmatched: '*1 passed, 1 warnings*'

but I can't find where the request fixture is defined to investigate further. Do you know where it is, or why I'd see this error in CI but not locally?

[nicoddemus]

Oh we need to update the test suite for 4.1.0. I will do it in a separate PR.

[nicoddemus]

@aadamson you can merge/rebase on master to fix the Config.warn tests. 👍

[aadamson]

Done, thank you!

[nicoddemus]

Awesome, thank you!

[aadamson]

Thanks for your help! How do I merge?

[nicoddemus]

Only the maintainers can merge. 😁

I didn't merge yet in case @RonnyPfannschmidt wants to take a look first.