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taut

Fast Python test runner. Tests, without the overhead.

taut is a high-performance test runner for Python written in Rust. It uses smart dependency tracking to only re-run tests that could have been affected by your changes.

Features

  • Fast startup - Sub-100ms startup time, no Python import overhead
  • Smart caching - Only re-runs tests when their dependencies change
  • Block-level tracking - Tracks dependencies at function/class level, not file level
  • Zero config - Works out of the box with no setup required
  • Parallel execution - Runs tests in parallel with process isolation
  • Async support - async def test_* functions just work

Quick Example

# test_example.py
def test_addition():
    assert 1 + 1 == 2

def test_subtraction():
    assert 5 - 3 == 2

async def test_async_operation():
    result = await some_async_func()
    assert result == "expected"

$ taut
taut ..
2 passed, in 0.05s

# Change test_addition, only it re-runs:
$ taut
taut .
1 passed, 1 skipped (unchanged), in 0.03s

Why taut?

Traditional test runners re-run all tests when any file changes. taut tracks which code each test actually executes, so it knows exactly which tests need to re-run.

Feature taut pytest
Startup time ~50ms ~500ms+
Incremental runs Function-level File-level (with plugins)
Default isolation Process per test Shared process

Getting Started