cept it takes a second argument, which is the number of processes needed to run the test.  If the number of processes is less than 2, the test will fail. If the number of processes is greater than or equal to 2, it will create a sub-communicator over 2 processes, called ```test_comm```, and execute the test over these processes. Three objects are provided by ```MPI_TEST_CASE```:
 * ```test_comm```, of type ```MPI_Comm```: the mpi communicator on which the test is running,
 * ```test_rank``` and ```test_nb_p