rstest

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Run your existing pytest suite in parallel, unchanged. Same fixtures, same plugins, same outcomes — just faster. Rust-orchestrated, parallel by default, with built-in suite diagnostics (--doctor) that tell you where your test time actually goes.

aiohttp, 4,469 tests:   pytest 197s  →  rstest 68s

📚 Full documentation → python-rstest.readthedocs.io

Quick start

In any pytest project:

pip install rstest      # or: uv pip install rstest
rstest

Also works with your tool of choice:

uv add rstest           # uv projects
poetry add rstest       # Poetry
pdm add rstest          # PDM
pipx install rstest     # isolated CLI install

No config. No test changes. If pytest runs it, rstest runs it — in parallel (-n auto), out of the box.

  • Tests that can't run in parallel → @pytest.mark.serial (run exclusively, after the parallel phase).
  • Order-dependent suites → --dist loadfile.
  • Want byte-exact pytest semantics → rstest -n 0 (single pytest session).

Benchmarks

Real open-source suites, end-to-end, with per-test outcome diffing against the pytest baseline — 100% parity.

Suite Tests pytest xdist (-n 8) rstest
aiohttp 4,469 197s 160s 68s
pandas 193,627 182s 61s 63s
django-allauth 2,050 22s 8s 8s (-n 4)
rich 981 3.4s 2.8s 2.5s (-n 4)

Apple Silicon, CPython 3.13, pytest-xdist 3.8. Full methodology and monorepo numbers: benchmarks.

Why rstest

pytest pytest-xdist rstest
Runs your suite unchanged ✅ mostly ✅
Parallel by default ❌ ⚙️ opt-in ✅
Duration-aware scheduling ❌ ❌ ✅
Crashed workers respawn mid-run ❌ ❌ ✅
Suite diagnostics ❌ ❌ ✅ --doctor
Watch mode plugin ❌ ✅ built-in
  • Drop-in. Forwards the pytest flag surface; runs conftest, fixtures, parametrize, marks, and pytest plugins (pytest-django, pytest-asyncio, hypothesis, …) through a vendored pytest core.
  • Parallel by design. Test-granular work distribution with duration-aware scheduling; @pytest.mark.serial and --dist loadfile safety rails; crashed workers respawn without losing your run.
  • rstest --doctor. Wait-bound tests, parallel-floor analysis, fixture hotspots, slowest files.
  • rstest --watch. Instant reruns on save; changed test files rerun alone, source changes rerun only the tests the import graph says are affected.
Compatibility contract

At -n 0, outcomes are byte-exact. In parallel modes, outcomes are preserved for parallel-safe tests; tests with hidden time/ordering/shared-state assumptions can flake under high concurrency — exactly as under pytest-xdist. rstest --doctor and lower -n values help find and contain them; @pytest.mark.serial is the escape hatch.

rstest --doctor

Runs your suite, then answers where does the time actually go? — from data the runner already owns (per-test wall/CPU time, per-fixture setup):

================== rstest doctor ==================
4442 tests, 185.8s test time (wall 67.7s, 8 workers)

WAIT-BOUND: 95% of test time (176.5s) is waiting, not computing (sleeps / IO / timeouts).
    54.20s waiting of   54.25s  tests/test_proxy_functional.py::test_proxy_https_multi_conn_limit
  ... and 33 more

PARALLEL FLOOR: the longest test (54.2s) exceeds the ideal per-worker share (23.2s at -n 8);
no worker count can finish faster than its longest test.

FIXTURE HOTSPOTS (setup time across all workers):
     0.79s   4442x  scope=function blockbuster

SLOWEST FILES:
   150.46s (81.0%)  tests/test_proxy_functional.py
===================================================

That's aiohttp's real suite — one file is 81% of total test time, almost all of it waiting on 10-second proxy timeouts. More →

Docs

License

Licensed under either of

at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

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Maintainer: Kovant AB

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Python >=3.10

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