rtest 0.0.37

Python test runner built in Rust

rtest

A Python test runner built with Rust, currently supporting high-performance test-collection, with the goal of being a drop-in replacement for pytest.

⚠️ Development Status: This project is in early development (v0.0.x). Expect bugs, breaking changes, and evolving features as we work toward stability.

Performance

Benchmarks performed using hyperfine with 20 runs, 3 warmup runs per measurement, on an M4 Macbook Pro with 14 cores and 48GB RAM. More sophisticated benchmarks will be implemented in the future.

Against the flask Repository

hyperfine --command-name pytest --command-name rtest "pytest --collect-only" "rtest --collect-only" --warmup 3 --runs 20
Benchmark 1: pytest
  Time (mean ± σ):     229.9 ms ±   2.6 ms    [User: 184.5 ms, System: 37.4 ms]
  Range (min … max):   226.0 ms … 235.4 ms    20 runs

Benchmark 2: rtest
  Time (mean ± σ):      35.8 ms ±   1.2 ms    [User: 18.1 ms, System: 10.7 ms]
  Range (min … max):    34.2 ms …  40.3 ms    20 runs

Summary
  rtest ran
    6.41 ± 0.23 times faster than pytest

Against the httpx Repository

hyperfine --command-name pytest --command-name rtest "pytest --collect-only" "rtest --collect-only" --warmup 3 --runs 20
Benchmark 1: pytest
  Time (mean ± σ):     310.1 ms ±  18.6 ms    [User: 259.3 ms, System: 42.6 ms]
  Range (min … max):   291.0 ms … 344.4 ms    20 runs

Benchmark 2: rtest
  Time (mean ± σ):      20.6 ms ±   1.0 ms    [User: 12.5 ms, System: 5.5 ms]
  Range (min … max):    18.6 ms …  21.9 ms    20 runs

Summary
  rtest ran
   15.06 ± 1.15 times faster than pytest

Against the pydantic Repository

hyperfine --command-name pytest --command-name rtest "pytest --collect-only" "rtest --collect-only" --warmup 3 --runs 20
Benchmark 1: pytest
  Time (mean ± σ):      2.777 s ±  0.031 s    [User: 2.598 s, System: 0.147 s]
  Range (min … max):    2.731 s …  2.864 s    20 runs

Benchmark 2: rtest
  Time (mean ± σ):      61.2 ms ±   1.1 ms    [User: 40.1 ms, System: 14.4 ms]
  Range (min … max):    60.1 ms …  64.2 ms    20 runs

Summary
  rtest ran
   45.39 ± 0.95 times faster than pytest

Quick Start

Installation

pip install rtest

Requires Python 3.9+

Basic Usage

# Collect tests (fast AST-based collection)
rtest --collect-only

# Run tests using pytest as executor (default)
rtest

# Run tests using native runner (no pytest dependency)
rtest --runner native

Native Runner

The native runner (--runner native) executes tests without requiring pytest, using rtest's own decorators:

import rtest

@rtest.mark.parametrize("value", [1, 2, 3])
def test_example(value):
    assert value > 0

@rtest.mark.skip(reason="Not implemented yet")
def test_skipped():
    pass

The native runner respects python_files, python_classes, and python_functions patterns from your pyproject.toml under [tool.pytest.ini_options].

Roadmap

Support executing tests, with parallelization built out of the box (bypassing pytest-xdist). Currently, this works for some cases, but is not yet stable.

Known Limitations

Parametrized Test Discovery

rtest expands parametrized tests during collection when the decorator arguments are literal values (numbers, strings, booleans, None, lists/tuples of literals). For example:

@pytest.mark.parametrize("value", [1, 2, 3])
def test_example(value):
    assert value > 0

Both pytest and rtest collection show:

test_example[0]
test_example[1]
test_example[2]

However, when parametrize arguments contain dynamic expressions (variables, function calls, comprehensions), rtest cannot statically analyze them and will emit a warning while falling back to the base test name:

DATA = [1, 2, 3]

@pytest.mark.parametrize("value", DATA)  # Dynamic - references a variable
def test_example(value):
    assert value > 0

warning: Cannot statically expand test cases for 'test.py::test_example': argvalues references variable 'DATA'

In these cases, test execution is still functionally equivalent - pytest automatically runs all parametrized variants when given the base function name.

Test Class Inheritance Collection

When a test class inherits from another test class, rtest collects inherited test methods differently than pytest. While pytest shows inherited methods under each subclass that inherits them, rtest currently shows inherited methods only under the base class where they are defined. For example:

# test_example.py
class TestAddNumbers:
    def test_add_positive_numbers(self):
        pass

    def test_add_negative_numbers(self):
        pass

# test_floating_numbers.py
from tests.test_example import TestAddNumbers

class TestAddFloatingNumbers(TestAddNumbers):
    def test_add_simple_floats(self):
        pass

pytest collection shows:

test_example.py::TestAddNumbers::test_add_positive_numbers
test_example.py::TestAddNumbers::test_add_negative_numbers
test_floating_numbers.py::TestAddNumbers::test_add_positive_numbers
test_floating_numbers.py::TestAddNumbers::test_add_negative_numbers
test_floating_numbers.py::TestAddFloatingNumbers::test_add_positive_numbers
test_floating_numbers.py::TestAddFloatingNumbers::test_add_negative_numbers
test_floating_numbers.py::TestAddFloatingNumbers::test_add_simple_floats

rtest collection shows:

test_example.py::TestAddNumbers::test_add_positive_numbers
test_example.py::TestAddNumbers::test_add_negative_numbers
test_floating_numbers.py::TestAddFloatingNumbers::test_add_positive_numbers
test_floating_numbers.py::TestAddFloatingNumbers::test_add_negative_numbers
test_floating_numbers.py::TestAddFloatingNumbers::test_add_simple_floats

We believe this difference is desirable, in that TestAddNumbers isn't collected twice from different modules.

Path Separator Handling

rtest uses platform-specific path separators in test nodeids, while pytest normalizes all paths to use forward slashes (/) regardless of platform. For example:

On Windows:

• pytest shows: tests/unit/test_example.py::test_function
• rtest shows: tests\unit\test_example.py::test_function

On Unix/macOS:

• Both show: tests/unit/test_example.py::test_function

This difference is intentional as rtest preserves the native path format of the operating system.

Contributing

We welcome contributions! See Contributing Guide.

License

MIT - see LICENSE file for details.

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Acknowledgments

This project takes inspiration from Astral and leverages crates from [ruff].