A while ago Cactus' testsuite system gained the ability to run tests with “N” MPI ranks along with those requiring “N+1” (or greater) MPI ranks. This has the side effect that it is impossible to run only the tests requiring “N+1” ranks, since the “N” rank tests will always be included.

This is somewhat surprising and has lead to confusion about which tests are failing. A method to run only on the precise number of MPI ranks set in CCTK_TESTSUITE_RPOCESSORS (or whatever it s name is) should be provided, eg for use by the automated testing system (which runs 1 and 2 ranks anyway to tests thorns that do not specify a preference for both numbers of MPI ranks).

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2624/not-possible-to-run-tests-ony-on-2-or-more