Allow Gromacs tests to be run on a single rank

[xiki-tempula]

Prerequisites

So it might be good to specify -ntmpi 1 for gromacs test runs as some gromacs runs might fail on machine with more cores.

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Expected Behavior

pytest -v test
will work.

Current Behavior

On my machine with 10 cores. The test

test_gromacs
  test_equilibrate
  test_heat
  test_production

will fail giving the error

-------------------------------------------------------
Program:     gmx mdrun, version 2022
Source file: src/gromacs/domdec/domdec.cpp (line 2232)
MPI rank:    0 (out of 10)

Fatal error:
There is no domain decomposition for 10 ranks that is compatible with the
given box and a minimum cell size of 0.8525 nm
Change the number of ranks or mdrun option -rdd or -dds
Look in the log file for details on the domain decomposition

For more information and tips for troubleshooting, please check the GROMACS
website at http://www.gromacs.org/Documentation/Errors
-------------------------------------------------------

The easiest solution would be: When runing these tests, add the flag -ntmpi 1 to the gmx mdrun

[lohedges]

Thanks for this. My local build of GROMACS is compiled without MPI support so I don't experience this issue. I'll add this when I get a chance since it would be good to allow tests to run against different builds.

Cheers.

[xiki-tempula]

@lohedges Thanks. I could verify that now the unit tests are passing.