This will ensure we don't forget to add any data files to the MANIFEST.in (which means test data is not available to the inlined tests).
{posargs} allows to pass extra arguments to the test runner, when runing `tox -- {posargs}` from the command line.
With `--pyargs` option, pytest tries to interpret arguments as python package/module names, and if import fails as regular filesystem paths.
When running `tox` command without specifying any `-e` option, or when no $TOXENV environment variable is specified, the 'envlist' in tox.ini file determines the list of environment tox will operate on.
http://tox.readthedocs.io/en/latest/config.html#confval-envlist=CSV
I chose Python 2.7 and 3.5 because I assume they are the versions that other fonttols developers run their tests on locally, before pushing and let the CI run the tests on the rest of the pythons.
The glob pattern determines which classes are considered for test collection by pytest.
We already follow this pattern for the unittest.TestCase derived subclasses
(which are collected regardless of this option).
the glob pattern will restricts the search only for pytest's kind of tests; it has no effect on methods of unittest.TestCase derived class, since pytest still uses unittest's own collection framework to collect those.
The 'minversion' is required to support some of the latest advanced features.
The current py.test is 2.8.7. You can update it with `pip install --upgrade pytest`.
