tests: skip tests without xmlschema

[blueyed]

No description provided.

[bluetech]

Given that this package is in the testing extra, when will it not be available?

[blueyed]

It does not have to be installed necessarily, i.e. when just doing pip install -e ..
This is just for convenience, and leaves a better impression when tests are working out of the box.
(it will still fail due to hypothesis here, but that's not easy to fix)
Feel free to close, I just thought it's easy to upstream.

[nicoddemus]

Thanks @blueyed, but this means most (if not all) tests from junitxml will get skipped if the user does not have xmlschema installed. This might be frustrating because a user will inavertidely get a successfull test run, but there might be broken junitxml tests which will only appear then in CI.

I prefer we advertise users working on the tests to always use pip install -e .[testing] to avoid our test suite having to work around incomplete virtual environments.