rpytest

Run your pytest suite faster. Change nothing.

rpytest is a Rust-powered, drop-in replacement for pytest that eliminates startup and collection overhead while keeping your existing tests, fixtures, and plugins completely untouched.

Website · Documentation · GitHub

# Install and run - that's it
pip install rpytest
rpytest

Why rpytest?

Metric	pytest	rpytest	Improvement
Wall clock (480 tests)	2.91s	1.55s	1.9x faster
CLI memory usage	35.8 MB	6.2 MB	5.8x less

The speed comes from a persistent daemon that keeps Python warm between runs. No more paying interpreter startup costs on every invocation.

Installation

# Via pip (recommended)
pip install rpytest

# Via Homebrew (macOS / Linux)
brew tap neul-labs/tap
brew install rpytest

# Via npm
npm install -g rpytest

# Via cargo (installs both the CLI and the daemon)
cargo install rpytest rpytest-daemon

# From source
git clone https://github.com/neul-labs/rpytest.git
cd rpytest
cargo install --path crates/rpytest
cargo install --path crates/rpytest-daemon

Note: rpytest requires the rpytest-daemon binary to function. Both packages must be installed when using cargo install.

Usage

rpytest mirrors pytest's CLI exactly. If you know pytest, you know rpytest.

# Run all tests
rpytest

# Run specific tests
rpytest tests/test_api.py::test_login

# Filter by keyword or marker
rpytest -k "auth" -m "not slow"

# Parallel execution (pytest-xdist compatible, no plugin needed)
rpytest -n auto

# Watch mode for TDD
rpytest --watch

# Verify identical behavior to pytest
rpytest --verify-dropin

Key Features

Instant Startup

The first run spawns a background daemon. Every subsequent run is a fast RPC call—no interpreter startup, no re-importing your test modules.

Full pytest Compatibility

• All pytest CLI flags work identically
• Your plugins, fixtures, and conftest.py files run unchanged
• pytest.ini, pyproject.toml, and tox.ini configs are respected
• Exit codes and JUnit XML match pytest exactly

Built-in Parallelism

rpytest -n 4  # Run on 4 workers
rpytest -n auto  # Auto-detect based on CPU cores

No pytest-xdist required. Duration-aware load balancing included.

Watch Mode

rpytest --watch

File changes trigger automatic re-runs of affected tests.

Flakiness Detection

rpytest --reruns 3  # Auto-retry failed tests
rpytest --flaky-report  # See which tests are flaky

Sharding for CI

rpytest --shard 0 --total-shards 4  # Perfect for parallel CI jobs

How It Works

1. First run: Spawns a Python daemon that collects your test suite once
2. Subsequent runs: Rust CLI filters tests and dispatches to warm Python workers
3. Results stream back in real-time for instant feedback

The daemon persists between runs, so repeated invocations (TDD loops, CI retries, --last-failed) skip all the startup work.

Daemon Management

rpytest --daemon-status  # Check health
rpytest --daemon-stop    # Stop the daemon
rpytest --cleanup        # Clean stale contexts

Drop-in Guarantee

Run the verification harness to confirm identical behavior:

rpytest --verify-dropin

This runs both pytest and rpytest on your suite and compares collection counts, pass/fail results, and exit codes.

Configuration

rpytest reads your existing pytest configuration—no new config files needed:

• pytest.ini
• pyproject.toml ([tool.pytest.ini_options])
• tox.ini
• setup.cfg

Documentation

Full documentation at docs.neullabs.com/rpytest

Contributing

Contributions welcome!

git clone https://github.com/neul-labs/rpytest.git
cd rpytest
cargo build
cargo test

Part of the Neul Labs toolchain

Explore the rest of the Neul Labs developer tools:

Project	Description
rjest	A blazing-fast, Jest-compatible test runner — 100x faster warm runs.
rninja	Drop-in Ninja replacement with built-in caching.
gity	Make large Git repositories feel instant.
stkd	Stacked diffs for GitHub and GitLab.
grite	The issue tracker that lives in your repo. Built for AI agents.

Learn more at neullabs.com.

License

Licensed under the MIT License.