Test Isolation

ELI5 — The Vibe Check

Test Isolation means each test is completely independent — it sets up its own data, runs in its own world, and cleans up after itself. No test depends on another test's data or execution order. It's the 'leave no trace' principle applied to testing.

Real Talk

Test isolation ensures tests don't share state, depend on execution order, or interfere with each other. Techniques include per-test database transactions (rolled back after each test), unique test data, isolated containers, mocked external services, and cleanup hooks. Essential for reliable, parallelizable test suites.

When You'll Hear This

"Each test runs in a database transaction that rolls back — complete isolation." / "Test isolation means we can run all 2000 tests in parallel without flakes."