Make test pass when run with 'tox'

[mgedmin]

I used to get failures like

py27 runtests: commands[0] | zope-testrunner --test-path=.
Test-module import failures:

Module: persistent.tests.test_docs

IOError: [Errno 2] No such file or directory: '/home/mg/src/zopefoundation/persistent/.tox/docs/api/cache.rst'

Running zope.testrunner.layer.UnitTests tests:
  Set up zope.testrunner.layer.UnitTests in 0.000 seconds.
  Ran 524 tests with 0 failures, 1 errors and 0 skipped in 0.249 seconds.
Tearing down left over layers:
  Tear down zope.testrunner.layer.UnitTests in 0.000 seconds.

Test-modules with import problems:
  persistent.tests.test_docs
ERROR: InvocationError for command '/home/mg/src/zopefoundation/persistent/.tox/py27/bin/zope-testrunner --test-path=.' (exited with code 1)

because adding a ../ at the end of the path is not the same as stripping off the last path component when symlinks are involved!

$ cd .tox && ./py27/bin/python
>>> >>> from persistent.tests.test_docs import __file__
>>> __file__
'/home/mg/src/zopefoundation/persistent/.tox/py27/local/lib/python2.7/site-packages/persistent/tests/test_docs.pyc'

.tox/py27/local/lib is a symlink to /home/mg/src/zopefoundation/persistent/.tox/py27/lib and so .tox/py27/local/lib/.. is pointing to .tox/py27, while os.path.abspath() thinks it's pointing to .tox/py27/local.

>>> import os
>>> here = os.path.dirname(__file__)
>>> while not os.path.exists(os.path.join(here, 'setup.py')): here = os.path.join(here, '..')
...
>>> here
'/home/mg/src/zopefoundation/persistent/.tox/py27/local/lib/python2.7/site-packages/persistent/tests/../../../../../../..'
>>> os.path.abspath(here)
'/home/mg/src/zopefoundation/persistent/.tox'
>>> os.path.exists(os.path.join(here, 'setup.py'))
True
>>> os.path.exists(os.path.join(os.path.abspath(here), 'setup.py'))
False
>>> os.path.exists(os.path.abspath(os.path.join(here, 'setup.py')))
False

[jamadden]

Interesting. Are you on an Ubuntu derivative, by any chance? I don't have that issue on macOS.

[jamadden]

tox -e py27 still works for me after this change, but it worked before too. If this fixes things for you, then LGTM.

(I think I wrote that code, sorry for the breakage!)

[mgedmin]

I'm on Ubuntu 18.04 LTS, yes.

I think this may be dependent on virtualenv's version? The local/* symlink tree differs between different virtualenv versions (previously I remember seeing a single local -> . symlink, now it's a directory with symlinks).

I have the very latest virtualenv (16.0.0).

The other thing it might depend on sys.path in the virtualenv'ed Python (i.e. does local/lib/site-packages come before lib/site-packages?), which might depend on my distro Python (or my distro Python's site.py/sitecustomize.py?).

I don't have motivation to dig too deep; it's sufficient for me to know that there exists a situation where appending .. doesn't work. ;)