pytest-rs 0.0.4

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, custom collectors (pytest_collect_file → File/Item), 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). Verified status:

evidence	plugins
own upstream test suite runs under pytest-rs and gates CI (per-suite pass-rate in the Third-party plugins conformance table below)	pytest-timeout, pytest-randomly, pytest-env, pytest-socket, pytest-snapshot, pytest-ruff, pytest-rerunfailures, pytest-order, pytest-repeat, pytest-instafail, pytest-icdiff, pytest-metadata, pytest-subtests, pytest-mypy, pytest-bdd, pytest-django; anyio's own plugin module also loads this way
functional smoke demo gates CI (conformance/plugin_smoke.py)	Faker, time-machine, requests-mock, inline-snapshot (snapshot assertions + --inline-snapshot flag), pytest-run-parallel (--parallel-threads really runs each test on N threads)
reporter replacement — 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)
not reimplemented yet	pytest-html (needs the report data model exposed); syrupy (serializer/extension framework)

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	1861	356	4	24	2245	82.9%	8	45	63
pytest-asyncio	v1.4.0	268	0	0	0	268	100.0%	30	30	0
pytest-mock	v3.15.1	87	0	0	1	88	98.9%	1	1	0
pytest-cov	v7.1.0	186	20	0	3	209	89.0%	0	1	0
pytest-xdist	v3.8.0	90	8	0	0	98	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
anyio	4.13.0	3120	0	0	42	3162	98.7%	26	26	0

Third-party plugins (not reimplemented — their own upstream test suites run under pytest-rs, loaded via the pytest11 entry-point shim):

suite	tag	passed	failed	errors	skipped	total	pass %	files all-pass	files run	files excluded
pytest-timeout	2.4.0	40	0	0	1	41	97.6%	1	1	0
pytest-mypy	v1.0.1	24	54	0	0	78	30.8%	0	1	0
pytest-ruff	v0.5	10	0	0	0	10	100.0%	1	1	0
pytest-subtests	v0.14.2	10	22	0	0	32	31.2%	0	1	0
pytest-metadata	v2.0.4	5	5	0	0	10	50.0%	0	1	0
pytest-snapshot	v0.9.0	100	7	0	0	107	93.5%	0	3	0
pytest-icdiff	0.5	7	5	0	0	12	58.3%	0	1	0
pytest-socket	0.7.0	59	6	0	0	65	90.8%	2	6	0
pytest-order	v1.4.0	85	49	0	0	134	63.4%	3	16	0
pytest-repeat	v0.9.4	11	5	0	0	16	68.8%	0	1	0
pytest-instafail	v0.5.0	48	15	0	0	63	76.2%	0	1	0
pytest-env	1.6.0	67	8	0	0	75	89.3%	2	3	0
pytest-rerunfailures	9.1.1	34	13	0	1	48	70.8%	0	1	0
pytest-randomly	4.1.0	32	5	0	0	37	86.5%	0	1	0
pytest-bdd	8.1.0	37	101	0	1	139	26.6%	6	35	0
pytest-django	v4.9.0	146	69	0	1	216	67.6%	2	13	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.