skip MPI tests if they would be oversubscribing the available processors

unittest/CMakeLists.txt

@@ -31,6 +31,10 @@ if(BUILD_MPI)
     set(MPI_TEST_NUM_PROCS 1)
     set(MPI_TEST_WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
     cmake_parse_arguments(MPI_TEST "" "NAME;NUM_PROCS;WORKING_DIRECTORY" "COMMAND" ${ARGN})
+    # Do not add test when oversubscribing
+    if(MPI_TEST_NUMPROCS GREATER MPIEXEC_MAX_NUMPROCS)
+      return()
+    endif()
     list(GET MPI_TEST_COMMAND 0 EXECUTABLE)
     list(REMOVE_AT MPI_TEST_COMMAND 0)
     set(ARGS ${MPI_TEST_COMMAND})