Use more than 2 processes in testing

[holke]

The test runner is currently configured to use mpirun -np 2.
We should increase the number of parallel processes to at least 4.

This is configured in the variable SC_MPI_TEST_FLAGS or T8_MPI_TEST_FLAGS

[Davknapp]

Do you know where the variable is set?
Grepping for it only results in
t8code/Makefile.am:LOG_COMPILER = @T8_MPIRUN@ @T8_MPI_TEST_FLAGS@
and the search for T8_MPIRUN leads to the same, starting from a fresh download of t8code

[holke]

This is set in the sc library, so we would need to change it for sc and hence all packages using sc.

However, maybe writing a t8_mpi.m4 that overwrites the sc setting for T8_MPI_TEST_FLAG works?

https://github.com/cburstedde/libsc/blob/master/config/sc_mpi.m4

[cburstedde]

This is set in the sc library, so we would need to change it for sc and hence all packages using sc. However, maybe writing a t8_mpi.m4 that overwrites the sc setting for T8_MPI_TEST_FLAG works? https://github.com/cburstedde/libsc/blob/master/config/sc_mpi.m4

It would not be hard to query an environment variable and/or the configure line to make the number of test processes configurable. We'd be happy to consider proposed updates to sc.

[holke]

#1139 #1134 add configure options to control the number of processes that tests are run on.

The only remaining step is to add more than 2 processes to the CI.

Also related to #1088

[Davknapp]

Our CI now uses 4 procs to test and one can also provide a custom command in the CMake build-system to execute the tests.