5. Run tests against all available environments:

.. warning::

   The ``--workdir`` option should be used in order to avoid mixing of

   Python cache files from the host and the Vagrant virtual

   machine, and to avoid getting the error ``ERROR: Could

   not install packages due to an EnvironmentError: [Errno 39]

   Directory not empty: '__pycache__'`` during installation of

   Gimmecert package inside of Tox virtual environment. It is unclear

   at time of this writing why such an error would be triggered, but

   it could have something to do with the ``vboxsf`` filesystem used

   for sharing the ``/vagrant`` directory.

::

     tox --workdir /tmp/