rtest 0.0.42

Python test runner built in Rust

rtest

A Python test runner built with Rust, featuring high-performance test collection and parallel test execution.

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

Performance

Test Collection (--collect-only)

Benchmarks performed using hyperfine with the following command:

hyperfine --warmup 3 --min-runs 20 --max-runs 20 \
  --command-name pytest --command-name rtest \
  ".venv/bin/pytest --collect-only -q tests" \
  ".venv/bin/rtest --collect-only tests"

Repository	pytest	rtest	Speedup
flask	226 ms ± 5 ms	34 ms ± 11 ms	6.57x
click	221 ms ± 10 ms	38 ms ± 7 ms	5.77x
httpx	344 ms ± 12 ms	33 ms ± 4 ms	10.56x
pydantic	1.60 s ± 21 ms	82 ms ± 13 ms	19.52x
fastapi	1.59 s ± 20 ms	62 ms ± 5 ms	25.57x
more-itertools	156 ms ± 5 ms	29 ms ± 5 ms	5.32x
boltons	234 ms ± 7 ms	35 ms ± 3 ms	6.77x

Test Execution (--runner native)

For repositories that don't rely on pytest fixtures or conftest.py, the native runner can execute tests directly:

hyperfine --warmup 3 --min-runs 20 --max-runs 20 \
  --command-name pytest --command-name rtest \
  ".venv/bin/pytest tests" \
  ".venv/bin/rtest --runner native tests"

Repository	pytest	rtest	Speedup
flask	764 ms ± 15 ms	205 ms ± 5 ms	3.72x
more-itertools	8.90 s ± 194 ms	1.34 s ± 185 ms	6.65x

Note: Native runner execution benchmarks are limited to repositories that use simple test patterns (unittest.TestCase, plain assertions) without pytest fixtures. Most real-world projects use fixtures and conftest.py, which require the native runner's fixtures support (in development).

Test Execution (--runner pytest -n 4)

For repositories that use pytest fixtures and conftest.py, rtest can use pytest as the execution backend while still benefiting from fast Rust-based collection:

hyperfine --warmup 3 --min-runs 20 --max-runs 20 \
  --command-name pytest --command-name rtest \
  ".venv/bin/pytest -n 4 tests" \
  ".venv/bin/rtest --runner pytest -n 4 tests"

Repository	pytest	rtest	Speedup
more-itertools	8.96 s ± 218 ms	1.48 s ± 240 ms	6.04x

Note: Most repositories have limited --runner pytest benchmarks due to test ID generation differences between rtest and pytest for certain parametrized values. When rtest generates a different test ID than pytest expects, pytest cannot locate the test.

Quick Start

Installation

pip install rtest

Requires Python 3.10+

Basic Usage

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

# Run tests with native runner
rtest --runner native

# Run tests in parallel (4 workers)
rtest --runner native -n 4

Native Runner

The native runner (--runner native) executes tests using rtest's own decorators:

import rtest

@rtest.mark.cases("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].

For compatibility, @pytest.mark.parametrize and @pytest.mark.skip decorators are also supported.

Roadmap

• Fixtures - @rtest.fixture with function/class/module scopes and dependency resolution
• conftest.py support - Fixture discovery across directory hierarchy
• Distribution modes - Group tests by module/class, optimized scheduling algorithms
• Cross-module constant resolution - Resolve constants imported from other modules in @rtest.mark.cases
• Built-in assertions - rtest.raises() and other assertion helpers
• Additional markers - @rtest.mark.xfail, @rtest.mark.skipif
• Test selection - -k expression filtering, --last-failed, --failed-first
• Better error formatting - Rich diffs, colorized output, traceback filtering
• Async test support - Native async def test_*() handling
• Watch mode - Re-run tests automatically on file changes

Known Limitations

Parametrized Test Discovery

rtest expands parametrized tests during collection when the decorator arguments can be statically resolved. This includes:

• Literal values: numbers, strings, booleans, None, lists/tuples of literals
• Module-level constants: DATA = [1, 2, 3] then @cases("x", DATA)
• Class constants: Config.MAX_SIZE
• Enum members: Color.RED
• Nested class constants: Outer.Inner.VALUE

from enum import Enum
import rtest

class Color(Enum):
    RED = 1
    GREEN = 2

DATA = [1, 2, 3]

@rtest.mark.cases("value", DATA)  # Resolves to [1, 2, 3]
def test_module_constant(value):
    assert value > 0

@rtest.mark.cases("color", [Color.RED, Color.GREEN])  # Resolves enum members
def test_enum_values(color):
    assert color.value in [1, 2]

However, rtest cannot statically analyze truly dynamic expressions and will emit a warning while falling back to the base test name:

from other_module import DATA  # Imported from another module

@pytest.mark.parametrize("value", DATA)
def test_example(value):
    assert value > 0

@pytest.mark.parametrize("value", get_data())  # Function call
def test_dynamic(value):
    assert value > 0

@pytest.mark.parametrize("value", [x for x in range(3)])  # Comprehension
def test_comprehension(value):
    assert value > 0

warning: Cannot statically expand test cases for 'test.py::test_example': argvalues references variable 'DATA'
warning: Cannot statically expand test cases for 'test.py::test_dynamic': argvalues contains function call 'get_data'
warning: Cannot statically expand test cases for 'test.py::test_comprehension': argvalues contains a comprehension

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

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].