pytest-delta 1.0.0

Run only tests impacted by your code changes (delta-based selection) for pytest.

pytest-delta

A pytest plugin that filters tests to only those affected by changes since the last successful run.

Installation

pip install pytest-delta

Usage

# Enable delta filtering
pytest --delta

# With debug output
pytest --delta --delta-debug

# With pytest-xdist for parallel execution
pytest --delta -n auto

CLI Options

Flag	Description
--delta	Enable delta filtering
--delta-file PATH	Custom delta file path (default: .delta.msgpack in project root)
--delta-debug	Show debug info: changed files, affected files, graph stats
--delta-pass-if-no-tests	Exit 0 when no tests need to run
--delta-no-save	Don't update delta file after run (read-only mode for CI/CD)
--delta-ignore PATTERN	Ignore file pattern (repeatable)
--delta-rebuild	Force rebuild dependency graph

Markers

import pytest

@pytest.mark.delta_always
def test_critical():
    """This test runs on every invocation regardless of changes."""
    ...

How It Works

1. On first run, builds a dependency graph by analyzing Python imports
2. Saves a .delta.msgpack file with the current commit SHA and graph
3. On subsequent runs, compares current state to last successful run
4. Only runs tests that depend on changed files (transitively)

CI Integration

# .github/workflows/test.yml
jobs:
  test:
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0  # Need full history for git diff

      - name: Run affected tests
        run: pytest --delta --delta-pass-if-no-tests -n auto

License

MIT