[ase-users] Major updates to testing: pytest, dockers

[Ask Hjorth Larsen]

Dear all,

We are porting the ASE test suite to pytest.  Running the tests will
now require pytest >= 3.3.2 and optionally pytest-xdist >= 1.22.1.
They can be installed via pip.

pytest provides some really nice and handy features like fixtures and
test parametrization, making it much easier to write properly
structured tests - which is exactly what we need right now.  So:

 * Use something like pip install --user pytest pytest-xdist
 * The 'ase test' tool will behave roughly as before, but output looks different
 * ase test --pytest <remaining args...>' can now be used to forward
options directly to pytest
 * pytest can also run on its own, independently of (some of) the test
suite code

The other big change is that the test pipelines now use custom docker
images.  In particular we want docker images with calculators
installed in order to run the calculator tests under controlled
environments.  This will be a major step towards normalizing the
behaviour and configuration of calculators.  The final step towards
achieving this goal is to write better tests.

Please report if there is any trouble.  There isn't supposed to be any
trouble, but we all know how that works.

Best regards
Ask