Parallel test fails if tblib is not installed.

[user0007]

The error occurs when NoSuchElementException (selenium) exception is raised:

test_changing_password (apps.users.tests.test_admin.UserAdminLiveServer) failed:

    NoSuchElementException()

Unfortunately, tracebacks cannot be pickled, making it impossible for the
parallel test runner to handle this exception cleanly.

In order to see the traceback, you should install tblib:

    pip install tblib

(...)

    subsuite_index, events = test_results.next(timeout=0.1)
  File "/usr/lib/python2.7/multiprocessing/pool.py", line 659, in next
    raise value
TypeError: can't pickle traceback objects

After installing tblib everything is ok:

(...)

----------------------------------------------------------------------
Ran 121 tests in 53.847s

FAILED (errors=2, skipped=2)

[Marten Kenbeek]

tblib was added as a new dependency to requirements/base.txt. Simply rerunning pip install -r tests/requirements/py3.txt (or py2.txt) solves any issues. Should the upgrade process be documented?

[user0007]

Replying to knbk:

tblib was added as a new dependency to requirements/base.txt. Simply rerunning pip install -r tests/requirements/py3.txt (or py2.txt) solves any issues. Should the upgrade process be documented?

But it fails running custom tests, not django tests. Should I add tblib to my all projects requirements.txt?

[Claude Paroz]

Requiring tblib is fine for Django itself, but clearly not for all user projects.

[Collin Anderson]

Would it make sense to just disable parallel tests if tblib is not installed?

[Aymeric Augustin]

This ticket's description is misleading. Parallel test *fail to report failures correctly and suggest to install tblib* when it isn't installed.

This is the intended and documented behavior. It was discussed on the DevelopersMailingList prior to the feature being implemented and committed. As shown in your description, there's a detailed explanation message. I'm not sure what else I could do.

You have three options, pick your favorite:

1) Don't run tests in parallel and get exactly the same behavior as in Django 1.8.
2) Have your tests crash hard if an exception occurs.
3) Install tblib.

Claude, in case this isn't clear, tblib is only required for getting correct failure reports when running tests in parallel.

Collin, I don't think it makes sense to ignore the --parallel option when tblib isn't installed. As long as tests complete without errors or failures, tblib isn't needed.

Of course as soon as you have a test failure you'll want to know why it fails. If you're absolutely unable to pip install tblib and absolutely need to run tests in parallel — I can't see why that would be the case, but for the sake of the argument let's assume at least one user will be in this situation — you can re-run just the failing test without the --parallel option.

If someone proposes a patch to improve the situation, we can reopen this discussion.