Minimal tests for test level 2

[lenaploetzke]

Describe your changes here:

• Restricted some maximum levels for test level 2.

• Deleted some duplicate tests.

• Cleanup

• Most important change is #define T8_CMESH_MAX_NUM_XYZ_TREES 1 instead of using 2 as in test level 1. I think this is ok for a minimal test, especially since this variable alone saves around 40 seconds. Of course, this significantly limits the test quality.

• Side note:
  Currently, for serial tests using AllCmeshsParam, we have unnecessary cases with do_partition and do_bcast (as we only use one processor). Doing a case distinction between parallel and serial is somehow complicated and produces more code, and the time gain is insignificant. If someone has a simple solution to this, it would be nice to include it.

Closes #1371.

All these boxes must be checked by the reviewers before merging the pull request:

As a reviewer please read through all the code lines and make sure that the code is fully understood, bug free, well-documented and well-structured.

General

• The reviewer executed the new code features at least once and checked the results manually

• The code follows the t8code coding guidelines

• New source/header files are properly added to the Makefiles

• The code is well documented

• All function declarations, structs/classes and their members have a proper doxygen documentation

• All new algorithms and data structures are sufficiently optimal in terms of memory and runtime (If this should be merged, but there is still potential for optimization, create a new issue)

Tests

• The code is covered in an existing or new test case using Google Test

Github action

• The code compiles without warning in debugging and release mode, with and without MPI (this should be executed automatically in a github action)

• All tests pass (in various configurations, this should be executed automatically in a github action)

  If the Pull request introduces code that is not covered by the github action (for example coupling with a new library):

  • Should this use case be added to the github action?
  • If not, does the specific use case compile and all tests pass (check manually)

Scripts and Wiki

• If a new directory with source-files is added, it must be covered by the script/find_all_source_files.scp to check the indentation of these files.
• If this PR introduces a new feature, it must be covered in an example/tutorial and a Wiki article.

License

• The author added a BSD statement to doc/ (or already has one)

Tag Label

• The author added the patch/minor/major label in accordance to semantic versioning.

[lenaploetzke]

With the proposed changes I now have a test suite runtime of around 53 seconds at test level 2 (with CMAKE_CUSTOM_PARALLEL_TEST_COMMAND=mpirun -n 4 and make test -j 32).

By far the longest test is
40/71 Test #40: t8_gtest_iterate_replace_serial ....................... Passed 17.58 sec.

[lenaploetzke]

At the moment, in the CI, we use TEST_LEVEL 1 if the event is a PR, otherwise we use 0 (and never 2). I think this is fine for now. We should keep in mind that we could speed up the CI if necessary.

[ole-alb]

Please split the PR to create cleaner PRs