Announcing mojo-pytest

mojo-pytest is a Mojo🔥 language test runner plugin for pytest. Try it for your mixed Python and Mojo codebases. Here are some tips and example command line usage...

What is Mojo

Mojo is a new programming language that bridges the gap between research and production by combining Python syntax and ecosystem with systems programming and metaprogramming features. Mojo is still young, but it is designed to become a superset of Python over time. source: Mojo docs

What is pytest

The pytest framework makes it easy to write small, readable tests, and can scale to support complex functional testing for applications and libraries. source: pytest docs

pytest, meet Mojo

This package implements a pytest plugin to discover and run Mojo tests, alongside your Python tests. Although pytest does not have any awareness of Mojo source or package structure, pytest is extensible. In summary, plugin.py calls mojo test in a sub-process and parses the outputs and exit codes.

Example test using Mojo standard library

This simple Mojo module shows testing native Mojo code, and also calling into a Python module for testing vs reference implementation.

# file: example_tests/my_package/test_fibonacci.mojo

from python import Python
from testing import assert_equal
from my_package.fibonacci import fibonacci


def test_fibonacci():
    """
    Test fibonacci 10th number.
    """
    expect = 55
    got = fibonacci(10)
    assert_equal(got, expect)


def test_fibonacci_reference():
    """
    Test mojo fibonacci versus python "reference" implementation.
    """
    py = Python.import_module("my_package.fibonacci")
    for n in range(0, 10):
        expect = py.fibonacci(n)
        got = fibonacci(n)
        assert_equal(got, expect)

pytest runs both the Python tests, and the Mojo tests. Example command line usage:

$ pytest --mojo-include example_src/ example_tests/

================================ test session starts =======================
platform darwin -- Python 3.12.6, pytest-8.3.3, pluggy-1.5.0
rootdir: /Users/guidorice/mojo/mojo-pytest
configfile: pyproject.toml
plugins: mojo-24.5
collected 6 items                                                          

example_tests/my_package/my_test.mojo .                              [ 16%]
example_tests/my_package/test_fibonacci.mojo ..                      [ 50%]
example_tests/my_package/test_fibonacci.py .                         [ 66%]
example_tests/my_package/test_fire.🔥 .                              [ 83%]
example_tests/my_package/test_random_tensor.mojo .                   [100%]

================================ 6 passed in 13.55s =======================

Check it out at the GitHub repo: https://github.com/guidorice/mojo-pytest.

info

For compatibility, mojo-pytest follows the version numbering of mojo, ex: v24.5.

tip

To increase testing speed, try running pytest in parallel mode

Contributor

Thanks to Leandro Leites Barrios @lleiets for contributions and suggesting the idea of using the pytest plugin API, instead of just a config script.

Further reading

• mojo-pytest GitHub repo: https://github.com/guidorice/mojo-pytest
• Mojo GitHub https://github.com/modularml/mojo
• Mojo and MAX engine docs

edits

• 2024-10-17 remove var from code snippets: it's optional in latest Mojo release.