message: use mpi for serial tests
  needed on ray
diff: @@ -81,7 +81,9 @@ foreach(SRC_FILE ${ALL_EXE_SRCS})
  if ( NOT is_parallel_test STREQUAL "p" )
  add_test(NAME ${TEST_NAME}_ser
  - COMMAND ${TEST_NAME} ${THIS_TEST_OPTIONS})
  + COMMAND ${MPIEXEC} ${MPIEXEC_NUMPROC_FLAG} 1
  + $<TARGET_FILE:${TEST_NAME}> ${THIS_TEST_OPTIONS}
  + ${MPIEXEC_POSTFLAGS})
  else()
  add_test(NAME ${TEST_NAME}_np=4
  COMMAND ${MPIEXEC} ${MPIEXEC_NUMPROC_FLAG} 4
  