Heuristic for factory-based test suites: pick the cheapest factory method that still satisfies the test. Use build_stubbed when you need a dependency object you won't interact with; build when you need an in-memory object and no DB interaction; create without associations when a DB row is required but related records aren't; full create only for genuine end-to-end or request tests. test-prof can automatically replace every create with build and log the tests that then fail so they can be rolled back to create selectively.