Independent tests

What does the merge request do?

Make unit tests generated out of ComparisonMixin individually callable. As unit tests collection happens by class inspection - the test classes are instantiated later - afaics the only way to do this is through a meta class, as parametrisation of TestCase derived classes doesn't work in pytest.

Usually, the tests are generated as cross product of comparisons and compare_file, as was already the case. For details see documentation: https://joneuhauser.gitlab.io/-/extensions/-/jobs/4767449256/artifacts/build/html/source/inkex.tester.html#inkex.tester.ComparisonMixin

Implementation notes

A few changes were required to make the tests run with this change:

• The ColorList extension didn't properly reset its state when it was run, so that the values accumulated in multiple tests. This was split into its own commit.
• The LoremIpsum and JitterNodes have an inherently random output, and thus the output of those tests directly depended on the order they were run in.
• The mechanism to specify the output file name from TestHershey was promoted into the superclass, so this code was removed.
• For the other extensions, the generation of IDs was - similarly to Lorem Ipsum - dependent on the order the tests were run in.

Side note: Changing the order of the comparisons entries now has no effect anymore since pytest calls the generated functions in alphabetic order.

Summary for release notes

Improvements to the unit testing framework for stock extensions.

Checklist

• Add unit tests (if applicable)
• Changes to inkex/ are well documented
• Clean merge request history