pytest-mpixec

pytest plugin for running individual tests with mpiexec

A test marked with mark.mpiexec will be run in a separate instance with mpiexec, instead of in the current process.

The subprocess test will be run with pytest, so fixtures and everything should still work!

The number of processes can be parametrized if you parametrize an argument called mpiexec_n.

Try it out

pip install pytest-mpiexec

And write tests that use mpiexec:

from mpi4py import MPI

@pytest.mark.mpiexec(n=2)
def test_my_mpi_code(fixtures):
  assert something

@pytest.mark.mpiexec
@pytest.mark.parametrize("mpiexec_n", [1, 2, 3])
def test_my_mpi_code(mpiexec_n):
    assert MPI.COMM_WORLD.size == mpiexec_n

Options

If your mpi executable is not mpiexec for some reason, you can specify it with:

pytest --mpiexec your-mpiexec

pytest-mpiexec tries to reduce noise while still showing useful info for failures. That means only one output should appear when everything's working. But parallel failures can be both noisy and confusing, so there are options here, exposed via the --mpiexec-report option:

The concise option is experimental and aims to strike a balance between the possibly omitted information from first_failure and the redundant noise of all_failures.

Caveats

If you use module or session-scoped fixtures, another instance will be running, so these can't conflict with other pytest runs (e.g. conflicting on ports, files, etc.)

Prior art

• pytest-mpi (helpers for tests run inside mpi - compatible with this package!)
• pytest-easyMPI (similar goal to this one, but takes a different approach)