Python unittest C/Fortran MPI functions resulting in MPI_Init function getting called after MPI_finalize

I am writing Python wrappers to a Fortran library which uses MPI (OpenMPI, if that's relevant). The problem I mention here also occurs exactly for Python wrappers to C libraries. I must use the inbuilt unittest Python package for testing the Python interface.

I have the following MWE which tries to find maximum and minimum integer across all processors. Here's the Fortran file:

! File mpitest.F90
module mpitest
    implicit none
    include "mpif.h"
    integer nranks
    integer rank

    contains

    !--------------------------------------------------!
    subroutine pympitest_init()
        implicit none
        integer ierror
        call MPI_INIT(ierror)
        call MPI_COMM_SIZE(MPI_COMM_WORLD, nranks, ierror)
        call MPI_COMM_RANK(MPI_COMM_WORLD, rank, ierror)
    end subroutine pympitest_init

    !--------------------------------------------------!
    subroutine get_max_integer(inint, outint)
        implicit none
        integer, intent(in) :: inint
        integer, intent(out) :: outint
        integer ierror
        call mpi_allreduce(inint,outint,1,mpi_integer,mpi_max,MPI_COMM_WORLD,ierror)
    end subroutine get_max_integer

    !--------------------------------------------------!
    subroutine get_min_integer(inint, outint)
        implicit none
        integer, intent(in) :: inint
        integer, intent(out) :: outint
        integer ierror
        call mpi_allreduce(inint,outint,1,mpi_integer,mpi_min,MPI_COMM_WORLD,ierror)
    end subroutine get_min_integer

    !--------------------------------------------------!
    subroutine pympitest_final()
        integer ierror
        call mpi_finalize(ierror)
    end subroutine pympitest_final

end module mpitest

The Python unit test file is given below, with some things that I have tried but don't help put in as comments:

#!/usr/bin/env python3
# Python file test_pympitest.py
from __future__ import print_function
import unittest
import numpy as np

from pympitest import mpitest as pm

#--------------------------------------------------------------------#
class Test_Fortran_MPI_functions(unittest.TestCase):
    """Unit test template for testing MPI functions."""

    #----------------------------------------------------------------#
    #def __init__(self):
    #    """Try MPI_Initialize -- Does not help."""
    #    print("Initializing MPI")
    #    pm.pympitest_init()

    #----------------------------------------------------------------#
    #def tearDown(self):
    #    """Try MPI_Finalize -- Does not help."""
    #    print("Finalizing MPI")
    #    pm.pympitest_final()

    #----------------------------------------------------------------#
    def setUp(self):
        """Initialize the unit test."""
        print("Initializing MPI")
        pm.pympitest_init()

        # We'll just test min. and max. of ranks across all PEs.
        self.inint = pm.rank

    #----------------------------------------------------------------#
    def tearDown(self):
        """Finalize the unit test."""
        print("Finalizing MPI")
        pm.pympitest_final()

    #----------------------------------------------------------------#
    #----------------------------------------------------------------#
    # Two Tests. If you comment out any one of the tests, then the
    # unit test runs fine. Keeping both uncommented thorws error
    # saying MPI_Init was called after MPI_Final, obviously since
    # the setUp and tearDown functions are called every time.
    #----------------------------------------------------------------#
    def test_get_min_integer(self):
        """Test get_min_integer function."""
        minint = pm.get_min_integer(self.inint)
        print("Minimum on processor {} = {}".format(pm.rank,minint))
        self.assertEqual(minint, 0)

    #----------------------------------------------------------------#
    def test_get_max_integer(self):
        """Test get_max_integer function."""
        maxint = pm.get_max_integer(self.inint)
        print("Maximum on processor {} = {}".format(pm.rank,maxint))
        self.assertEqual(maxint, pm.nranks-1)

#--------------------------------------------------------------------#
if __name__ == "__main__":
    unittest.main()

    # Tried the following. Does not help:
    # Calls MPI_Initialize but exits without calling MPI_Finalize.
    #print("Initializing MPI")
    #pm.pympitest_init()
    #unittest.main()
    #print("Finalizing MPI")
    #pm.pympitest_final()

The Fortran code is wrapped into Python module called pympitest using f2py, like so: f2py --f90exec="mpif90" -DNPY_NO_DEPRECATED_API=NPY_1_7_API_VERSION -c mpitest.F90 -m pympitest. The unit test is run on 4 processors like so: mpirun -np 4 python test_pympitest.py.

I want to keep all MPI unit tests in a single python file. In the different things I have tried out (see the comments in the Python file), the problem I have faced is that MPI_Initialize and MPI_Finalize either get called multiple times in a single run or only one of them gets called, all of which exit with an error.

How do I fix this so that the unit tests pass properly?

Edit (Addition): Putting the testing functions into separate Test_...(unittest.TestCase) classes within a single Python file also does not help. Splitting the MPI unit tests into different files and trying python -m unittest discover does not work, which is inconvenient. Testing a single wrapped MPI function per Python file and individually running the each Python file would work, but that is something I would rather avoid.