def METHOD_NAME(self):
    """
    Verify that all quantities make sense when ngroups = 1.
    """
    rank_world = MPI.COMM_WORLD.Get_rank()
    nprocs = MPI.COMM_WORLD.Get_size()
    m = MpiPartition(ngroups=1)
    self.assertEqual(m.ngroups, 1)
    self.assertEqual(m.rank_world, rank_world)
    self.assertEqual(m.rank_groups, rank_world)
    self.assertEqual(m.rank_leaders, 0 if rank_world == 0 else -1)
    self.assertEqual(m.nprocs_world, nprocs)
    self.assertEqual(m.nprocs_groups, nprocs)
    self.assertEqual(m.nprocs_leaders, 1 if rank_world == 0 else -1)
    self.assertEqual(m.proc0_world, rank_world == 0)
    self.assertEqual(m.proc0_groups, rank_world == 0)
    m.write()