Taal: sort and restructure tests

[sloede]

Following up on the conversation started in #299 (comment), we should - once all elixirs and tests are ported to Taal and no comparisons to Taam are needed anymore - sort all tests by dimension and equation name.

At this point, we should also consider if

1. it would make sense to further separate the tests by dimension and equation in different files for easier/faster testing (Mix more 3D elixirs and port correspondings tests #299 (comment))
2. we really need tests on 3 OSs for everything (Mix more 3D elixirs and port correspondings tests #299 (comment))

Re 1:
If we do this, we should keep an eye on the GitHub Actions usage limits, such as to not make testing slower again. OTOH, if we do separate by dimension and equation, it might be nice to provide "aggregate" test files that allow easy execution of similar tests, e.g., if one wants to run all 2D tests, or all Euler tests etc.

[ranocha]

1. it would make sense to further separate the tests by dimension and equation in different files for easier/faster testing

I don't think that's useful. Setting up Julia and building Trixi takes between one (Linux) and four minutes (Windows) per CI job. Moreover, most CI time is spent on compilation. Hence, we benefit from using fewer CI jobs in parallel. Our current setup is fine, I think. Nevertheless, I would like to sort the tests by equation in the test files.

2. we really need tests on 3 OSs for everything

Currently, we test 2D in serial and parallel on all three OS and everything else only on Linux. That's okay for me and scales well - we test all essential features possibly involving non-Julia-only dependencies on all three OS but restrict the more expensive tests to one OS.

[sloede]

OK, then let's leave the current setup of what is tested where (point 2) as it is.

Your arguments re 1) also make sense, thus for CI testing we should leave it as it is. However, for developing and intermediate testing I think it still would be nice to be able to run, e.g., just 2D/Euler tests. Right now, I always comment out half the document, which is annoying.

Thus, given that we keep the tests together by dimension for CI, would you still object to separating them into files sorted by equation for different reasons?

[ranocha]

Thus, given that we keep the tests together by dimension for CI, would you still object to separating them into files sorted by equation for different reasons?

No, that's totally okay for me 👍