Django Test Performance

Use this as the orchestration skill for speeding up a Django test suite. Do not start by changing settings blindly; first measure the suite and then pick the smallest safe optimization with a repeatable verification command.

Core Workflow

1. Establish a baseline.

• Run the same command developers or CI use.
• Capture wall-clock time, runner, settings module, database backend, worker count, and branch.
• If the cause is unclear, use django-test-profiling before changing behavior.

1. Classify the dominant cost.

• Startup/import/discovery: reduce collection scope and expensive app initialization.
• Database creation/migrations: reuse DB locally, squash migration history, or improve database storage.
• Per-test setup: reduce fixture data, use factories, and use setUpTestData.
• External backends: replace file storage, cache, task queues, and instrumentation with test-safe backends.
• Long tail of tests: parallelize after isolation checks.

1. Apply low-risk wins first.

• Fast password hasher.
• DEBUG = False in tests.
• Disable database serialization when serialized rollback is not needed.
• Disable debug toolbar, Sentry/Rollbar/APM initialization, and other instrumentation.
• In-memory or local test backends for storage, cache, and task queues.
• See speed-wins.md.

1. Improve data and structure.

• Use django-test-data for factory, fixture, setUpTestData, TestCase, and integration-vs-unit decisions.

1. Improve migrations and database setup.

• Use --keepdb or --reuse-db for local repeat runs.
• Force rebuilds when migration history changes.
• Prefer squashing migrations over disabling migrations globally.
• Keep the test database backend close to production unless the project is database-agnostic.

1. Parallelize only when safe.

• Use django-test-parallelization for order isolation, shared resources, and worker configuration.

1. Re-measure with the original baseline command.

• Report before/after runtime and the changed risk surface.
• Keep or revert each optimization based on measured impact and behavioral fidelity.

Default Commands

bash
time python manage.py test
python manage.py test --timing
python manage.py test --keepdb

time pytest
pytest --durations 20
pytest --reuse-db
pytest --create-db

Decision Rules

• If you cannot name the bottleneck, profile first.
• If a setting changes production-like behavior, keep the override narrow and document why tests remain representative.
• Avoid broad TESTING = True branches in application code; use explicit settings and test helpers.
• Do not swap PostgreSQL/MySQL/MariaDB projects to SQLite just for speed unless production is SQLite or the project intentionally supports many backends.
• Do not disable migrations as the normal path. If a legacy project insists, run real migrations in CI.
• Keep local speed shortcuts from hiding CI coverage. CI should run slow tests and migration-realistic paths somewhere.

Handoff Map

| Situation | Use | |-----------|-----| | Need timings, slow-test lists, flame graphs, or cProfile output | django-test-profiling | | Enabling --parallel, pytest-xdist, or debugging random failures | django-test-parallelization | | Fixture bloat, factories, setUpTestData, TestCase class choices | django-test-data | | Mocking settings, HTTP, time, output, or command input safely | django-targeted-mocking | | CI cache, split jobs, slow markers, runner scale | django-ci-test-optimization |

Verification

Before finishing, provide:

• Baseline and final runtime from the same command.
• A ranked list of changes made or recommended.
• Risks introduced by each test-only override.
• Commands the project should keep for local and CI verification.