pytest-rs 0.0.3

A fast, drop-in compatible pytest runner written in Rust

pytest-rs

pytest-rs is a re-implementation of the popular Python testing framework pytest in Rust, focused on speed: a drop-in compatible runner where startup, collection, fixture orchestration, coverage measurement, and reporting are native code, while test bodies run on embedded CPython.

Note: This project is currently in active development (alpha stage). Many features are still under implementation and subject to change. See docs/DESIGN.md for the architecture and roadmap.

pytest-rs is an independent project, not affiliated with or endorsed by the pytest project.

Installation

Prebuilt wheels are published to PyPI for Linux (x86_64 / aarch64) and macOS (arm64) on CPython 3.13 / 3.14:

uv add --dev pytest-rs    # or: pip install pytest-rs

Then run your existing suite, no changes needed:

pytest-rs                       # whole suite, like `pytest`
pytest-rs tests/test_foo.py     # one file
pytest-rs -n 4                  # parallel workers (pytest-xdist compatible)
pytest-rs --cov=mypkg           # native coverage (pytest-cov compatible)

pytest-rs reads the same configuration pytest does (pytest.ini, pyproject.toml [tool.pytest] / [tool.pytest.ini_options], tox.ini, setup.cfg) and understands the familiar flags (-v, -x, -k, -m, --lf, --tb=..., -p no:NAME, ...). It installs alongside pytest without conflict — the pytest command is untouched.

Requirements

• Linux or macOS (no Windows support yet)
• CPython 3.13+ built with a shared libpython — true for uv-managed Pythons, python.org installers, Homebrew, conda, and distro packages. Plain pyenv builds need PYTHON_CONFIGURE_OPTS="--enable-shared" pyenv install ....

Bundled plugins

The compatibility layers for pytest-asyncio, anyio's pytest plugin, pytest-mock, pytest-cov, pytest-split, pytest-benchmark and pytest-xdist-style -n parallelism are built in — no separate plugin installs (the anyio layer runs tests through the installed anyio library's backends, so anyio itself must be in the environment as usual). Two ways to turn features off:

Per project or per run, like pytest (works with the prebuilt wheel):

[tool.pytest.ini_options]
addopts = "-p no:benchmark -p no:split"

At build time, when installing from source — bundled plugins are Cargo features, all enabled by default:

[tool.uv]
config-settings-package = { pytest-rs = { build-args = "--no-default-features --features asyncio,mock" } }

Third-party plugins (not reimplemented, loaded as-is)

Installed pytest11 entry points load through the pytest API shim — plugins pytest-rs does not reimplement can still work as-is. The supported surface includes fixtures, markers, pytest_addoption (plugin --flags and ini options), config.stash, custom hookspecs (pytest_addhooks), pytest_runtest_protocol/pytest_runtest_call hookwrappers, and terminal-reporter replacement (a plugin that unregisters the terminalreporter plugin and registers its own subclass takes over the output — pytest-rs suppresses its native rendering and drives the replacement through the same hooks pluggy would). Spot-verified status:

status	plugins
works — upstream test suite gates CI	pytest-timeout (40/41, see conformance below); anyio's own plugin module also loads this way
works — plugin-smoke gates CI (functional demos, conformance/plugin_smoke.py)	Faker, time-machine, requests-mock, pytest-randomly (test reordering + seed header), inline-snapshot (snapshot assertions + --inline-snapshot flag), pytest-run-parallel (--parallel-threads really runs each test on N threads)
works — plugin-smoke gates CI (terminal output byte-diffed against real pytest 9.0.3)	pytest-pretty, pytest-sugar (progress bar, instant failures; activates on a tty or --force-sugar) — reporter replacement
not working yet	pytest-env — needs the pytest_load_initial_conftests early hook

A plugin that fails to import (e.g. it reaches into pytest/pluggy internals the shim doesn't provide) warns and is skipped without breaking the run. -p no:NAME and PYTEST_DISABLE_PLUGIN_AUTOLOAD opt out, like pytest.

Performance

Native startup, collection, fixture orchestration, parallel workers (fork-based) and coverage measurement. Where it pays off:

• suites with heavy fixture/parametrize orchestration and large collections
• --cov runs (a native collector instead of a tracing hook)
• -n parallel runs (fork workers instead of spawned interpreters)

For small, CPU-bound suites the test bodies dominate and pytest-rs runs at parity with pytest. Try it on your own suite:

hyperfine -w 1 'pytest -q' 'pytest-rs'

Known limitations

• unix only (no Windows)
• no --pdb / debugger integration yet
• third-party pytest plugins are loaded via the pytest11 entry point and the pytest API shim; plugins reaching deep into pytest internals may not work (see "Third-party plugins" above for verified examples)

Conformance testing

Compatibility is verified by running the upstream test suites of the libraries pytest-rs reproduces, unchanged, under pytest-rs (conformance/).

Current results (total = passed + failed + errors + skipped; updated automatically by conformance/runner.py, refreshed by CI on every push to main — see conformance/RESULTS.md for per-file detail):

linux (CI-verified)

pytest & plugin ecosystem (the APIs pytest-rs reimplements):

suite	tag	passed	failed	errors	skipped	total	pass %	files all-pass	files run	files excluded
pytest	9.0.3	1419	708	42	24	2193	64.7%	6	45	63
pytest-asyncio	v1.4.0	268	0	0	0	268	100.0%	30	30	0
pytest-mock	v3.15.1	85	0	0	5	90	94.4%	1	1	0
pytest-cov	v7.1.0	182	24	0	3	209	87.1%	0	1	0
pytest-xdist	v3.8.0	89	8	0	0	97	91.8%	0	1	6
pytest-split	0.9.0	59	0	0	0	59	100.0%	1	1	3
pytest-benchmark	v5.1.0	91	31	0	1	123	74.0%	4	7	6
pytest-timeout	2.4.0	40	0	0	1	41	97.6%	1	1	0
anyio	4.13.0	3120	0	0	42	3162	98.7%	26	26	0

Real-world projects (their suites run unchanged, as drop-in evidence):

suite	tag	passed	failed	errors	skipped	total	pass %	files all-pass	files run	files excluded
click	8.3.1	1314	0	0	21	1335	98.4%	20	20	0
jinja	3.1.6	909	0	0	0	909	100.0%	22	22	0
marshmallow	4.1.1	1119	0	0	0	1119	100.0%	12	12	3
rich	v14.2.0	855	0	0	25	880	97.2%	60	62	0

The suites are included as shallow git submodules under conformance/suites/ at the pinned release tags. Initialize them once after cloning:

git submodule update --init --depth 1

Then run the full conformance harness:

cargo build
uv run --no-project python conformance/runner.py --local   # uses submodules
uv run --no-project python conformance/runner.py           # re-clones from upstream (CI mode)

Project	License	Tag
pytest	MIT	9.0.3
pytest-asyncio	Apache-2.0	v1.4.0
pytest-mock	MIT	v3.15.1
pytest-cov	MIT	v7.1.0
pytest-xdist	MIT	v3.8.0
pytest-split	MIT	0.9.0
pytest-benchmark	BSD-2-Clause	v5.1.0

pytest-rs reimplements the public APIs of these projects, plus anyio's pytest plugin (MIT). Parts of the bundled Python shims are ports of upstream code; see THIRD-PARTY-NOTICES.md. Credit for the API design and the test suites belongs to their respective authors.

License

This project is licensed under the MIT License. See the LICENSE file for more details.