mojo-pytest

Mojo🔥 test runner using pytest.

Design

This package implements a pytest plugin to discover and run Mojo tests. Although pytest does not have any awareness of Mojo source or package structure, pytest is extensible. By following a convention, you can use pytest to run Mojo tests and view results. In summary, plugin.py calls mojo run in a sub-process and parses the outputs and exit codes.

Convention

• Create Mojo package directory in your project root.
• Anywhere in the Mojo package create source files prefixed with test_, ex: test_something.mojo or test_xyz.🔥. Files suffixed with _test are also collected, ex: something_test.mojo or xyz_test.🔥.
  • Each test file must have a main entry point function.
  • Each main function may call arbitrary functions and methods in your Mojo package.
  • Each test item must print a line with it's test name, prefixed with # (hashtag, comment) character, ex: # test name.
  • Failed tests should use one of the standard testing assertions. A helper struct for tests is available in example/tests/util.mojo. Tests will also fail if a Mojo Error is raised or if an unhandled exception occurs. Note that with unhandled exceptions, subsequent tests will not be collected.
• Mojo compiler warnings may optionally be handled as test failures, using the pytest -W error mode.
• Mojo debug assertion errors may optionally be handled as test failures, using the pytest --mojo-assertions mode.

Usage

1. Install pytest >= 7.4 in your Python environment.
2. Install pytest-mojo plugin with pip install git+https://github.com/guidorice/mojo-pytest.git, or with the Conda environment.yaml.
3. Use the project layout described in here.
4. Run pytest from your project root. See also pytest docs. Examples:

# summary
pytest

# details
pytest -v

# mojo warnings treated as errors
pytest -W error

# mojo assertion failures treated as errors (-D MOJO_ENABLE_ASSERTIONS)
pytest --mojo-assertions

# show all captured stdout
pytest -s

Example Project

In the example/ directory is a Mojo package with a couple of modules. Note: in every subdirectory also exists an __init__.mojo file, not shown here:

example
├── mod_a
│   └── impl.mojo
├── mod_b
│   └── impl.mojo
└── tests
    ├── mod_a
    │   ├── test_convert.mojo
    │   ├── test_convert_different.mojo
    │   └── test_maths.mojo
    ├── mod_b
    │   └── test_greet.mojo
    ├── suffix_test.mojo
    ├── test_debug_assert.mojo
    ├── test_warning.mojo
    └── util.mojo

$ pytest
============================= test session starts ==============================
platform darwin -- Python 3.11.9, pytest-7.4.3, pluggy-1.3.0
rootdir: /Users/guidorice/mojo/mojo-pytest
plugins: mojo-24.3.1
collected 18 items                                                             

example/tests/suffix_test.mojo .                                         [  5%]
example/tests/test_debug_assert.mojo .                                   [ 11%]
example/tests/test_warning.mojo .                                        [ 16%]
example/tests/mod_a/test_convert.mojo .                                  [ 22%]
example/tests/mod_a/test_convert_different.mojo .                        [ 27%]
example/tests/mod_a/test_maths.mojo ....F.......                         [ 94%]
example/tests/mod_b/test_greet.mojo .                                    [100%]

=================================== FAILURES ===================================
_______________________________  maths more: 42 ________________________________
(<MojoTestItem  maths more: 42>, '/.../mojo-pytest/example/tests/mod_a/test_maths.mojo:30:29: AssertionError: bad maths: 42')
=========================== short test summary info ============================
FAILED example/tests/mod_a/test_maths.mojo:: maths more: 42
========================= 1 failed, 17 passed in 1.90s =========================

Links

• Non-python tests in pytest: https://pytest.org/en/7.4.x/example/nonpython.html#non-python-tests
• C test runner: https://pytest-c-testrunner.readthedocs.io/