Testing taste of a pragmatic TypeScript team

• Use vitest as the default test runner for unit and integration tests. Confidence: 0.90
• Keep test files next to the code they cover as *.test.ts. Confidence: 0.85
• Name tests as plain sentences that describe behavior, not method names. Confidence: 0.90
• Follow arrange, act, assert with a blank line between each phase. Confidence: 0.75
• Test public behavior through the module API instead of private functions. Confidence: 0.90
• Prefer real collaborators and in-memory fakes over mocks. Confidence: 0.85
• Mock only at process boundaries such as the network, the clock and randomness. Confidence: 0.90
• Intercept HTTP with msw instead of stubbing fetch by hand. Confidence: 0.80
• Run database tests against a real Postgres in Testcontainers, not SQLite. Confidence: 0.80
• Freeze time with fake timers and pass seeds to anything random. Confidence: 0.90
• Build test data with small factory functions that accept overrides. Confidence: 0.85
• Keep snapshot tests rare and small, and review every snapshot diff. Confidence: 0.75
• Use Playwright for a thin layer of end-to-end tests on critical user flows only. Confidence: 0.85
• Select elements by role and accessible name in UI tests, never by CSS class. Confidence: 0.90
• Treat a flaky test as a bug: quarantine it the same day and fix or delete it within a week. Confidence: 0.85
• Never use sleep in tests; wait for an explicit condition instead. Confidence: 0.95
• Keep the full unit suite under one minute on a laptop. Confidence: 0.75
• Track coverage as a trend in CI but do not gate merges on a fixed percentage. Confidence: 0.70
• Add property-based tests with fast-check for parsers and pure logic. Confidence: 0.65
• Write a failing regression test before fixing every reported bug. Confidence: 0.90
• Run tests in random order to catch hidden shared state. Confidence: 0.70