Fix issue #553

[maurov]

This fixes #553 and adds basic tests

[maurov]

@newville the tests fail on Ubuntu. I have tried modifying the CI workflow recipe by including the DISPLAY environmental variable, but still fail. Do you have an idea how to fix it?

[newville]

@maurov I think the CI ubuntu virtual machines won't allow a DISPLAY to run. It's a common problem for GUI testing.

Maybe we can make a folder specifically for GUI tests that aren't run by the CI but make it easy for us to "run all the GUI tests".

[maurov]

@newville using pytest-xvfb permits correctly passing the GUI tests on Ubuntu.

There is still an error on Windows with python 3.9 that I do not understand. Do you have any suggestion?

[newville]

@maurov Hm, the failure for Windows and Python 3.9 seems to be something from pymatgen. I'm not sure I fully understand the error message.

[newville]

@maurov I would simply not run the test on Windows.

if os.name == 'nt':
    raise pytest.skip('skip GUI testing on Windows')

[maurov]

@newville I have skipped one failing test on Windows and python 3.9. Now everything looks fine and may be merged.

[newville]

@maurov OK, great, thanks!