Discover runner will raise AttributeError when test modules raise ImportError

[Hiroki Kiyohara]

When test modules raise ImportError, the discover runner will raise AttributeError.
It's difficult to detect the error reason.

I added a patch to check this problem.

ERROR: test_import_error_in_tests_module (test_runner.test_discover_runner.DiscoverRunnerTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/hirokiky/dev/django/django/tests/test_runner/test_discover_runner.py", line 172, in test_import_error_in_tests_module
    ["test_discovery_sample.tests_discovery_import_error"],
  File "/home/hirokiky/dev/django/django/django/test/runner.py", line 422, in build_suite
    tests = self.test_loader.loadTestsFromName(label)
  File "/usr/lib/python2.7/unittest/loader.py", line 100, in loadTestsFromName
    parent, obj = obj, getattr(obj, part)
AttributeError: 'module' object has no attribute 'tests_discovery_import_error'

[Tim Graham]

Not sure it can be solved or that it's Django's problem. From a ​python-tornado thread:

It's a problem with python's unittest module (or really it's a problem
with imprecise exception behavior from __import__ - you can't
distinguish between a module that doesn't exist and one that exists
but could not be loaded due to an internal ImportError). The unittest
loader wants to support loading individual classes and methods, so
when it sees an ImportError it just chops one level off the name and
looks it up later with getattr. I don't know of any workaround other
than just retrying the import outside the test loader context (as long
as you know it's supposed to be a module and not a class/method inside
the module). Python 2.7 made a lot of changes to the unittest module,
but this issue remains.

[Alexander Schepanovski]

This is very confusing behavior. I think it should be fixed even with a hack, like introspecting traceback.

[Tim Graham]

Accepting on the basis for further investigation.

[Chris Jerdonek]

I believe this issue corresponds to ​this Python issue, which is reported to be fixed in ​Python 3.5's changelog.

[Tim Graham]

I agree with that.