Testing Confidence Ladder

Testing everything at the UI level is slow and brittle. Testing nothing is reckless. The answer is layers: fast tests catch logic bugs, integration tests verify flows work together, visual tests catch UI regressions. This guide shows you how to build a test suite that actually helps instead of wasting time.

The Testing Layers

Each layer catches different bugs at different speeds. The pyramid principle still holds: lots of fast tests at the bottom, fewer slow tests at the top:

• Component tests: Fast, focused tests for individual UI components with Component Testing.
• Logic tests: Even faster tests for state management, reducers, and hooks with Stateful Logic Testing. No DOM, no rendering, just pure logic.
• Integration tests: Slower tests that verify multiple components work together with Integration Testing. Test routing, data fetching, shared state.
• Visual tests: Screenshot comparisons with Visual Regression catch UI changes you didn’t intend to make.
• Accessibility tests: Automated checks and manual screen reader testing with Accessibility Testing.

Create Maintainable Test Data

Copy-pasting giant JSON fixtures is how you build a test suite nobody wants to touch:

• Use test builders: Create Test Data Builder functions that generate valid test data with defaults. Need a user? buildUser(). Need one with a specific role? buildUser({ role: 'admin' }). Simple.
• Keep builders close: Store builders next to the code they support. When your data models change, tests break immediately and obviously. That’s good—it forces you to update everything at once.
• Provide smart defaults: Builders should work with zero config but let you override anything. Tests that fail with “Cannot read property ‘name’ of undefined” waste everyone’s time. Good builders prevent that.

Write Effective Component Tests

Component tests verify UI behavior without launching a browser. Keep them fast and focused:

• Mock minimally: Only mock what you have to. Let real context providers run, use real hooks, keep dependencies real when possible. Over-mocking makes tests useless—they pass but the real app breaks.
• Test user-facing behavior: Verify what users see and do. Does the button render? Does clicking it trigger the right action? Does the form validation work? Don’t test implementation details like state variable names; those are refactoring hazards.
• Keep tests fast: Component test suites should run in seconds. If they take minutes, something’s wrong. Fast tests get run on every save. Slow tests get skipped.

Test Complete User Journeys

Integration tests verify that components work together. They’re slower but catch issues component tests miss:

• Test critical paths: Use Integration Testing for essential flows: login, checkout, onboarding. Mock API calls with MSW but test real routing, real state management, real component interactions.
• Be selective: One integration test per critical user journey is enough. More than that and your suite becomes slow and flaky. If a test fails randomly 5% of the time, developers learn to ignore all test failures. Don’t let that happen.
• Verify analytics: Test that tracking events fire correctly. Broken analytics means you’re flying blind, and you won’t notice until someone asks why conversion metrics dropped.

Protect Visual Design and Accessibility

Automated tests verify logic. Visual and accessibility tests verify experience:

• Snapshot key screens: Run Visual Regression tests on design system components and critical pages. Test light/dark themes, different screen sizes. Catch accidental CSS changes before designers notice.
• Test accessibility automatically: Use Accessibility Testing to verify ARIA attributes, color contrast, keyboard navigation. Automated tools catch the obvious stuff. Manual screen reader testing catches the nuanced stuff. Do both.

Maintain Your Test Suite

Tests rot without maintenance. Treat your test suite like production code:

• Track layered coverage: Overall coverage percentages are meaningless. Track which critical flows have component tests, integration tests, visual tests, accessibility tests. Gaps in critical flows are risks.
• Fix flaky tests immediately: A test that passes sometimes and fails sometimes is worse than no test. It trains developers to ignore failures. Fix flaky tests the same day they appear, or delete them. No middle ground.
• Match tests to workflow: Run fast tests (component, logic) on every commit. Run slower tests (integration, visual) on pull requests. Run comprehensive accessibility audits before releases. Fast feedback loops matter.

Remember: The best test suite is the one your team actually runs. Fast, focused, reliable tests get used. Slow, flaky, comprehensive-to-a-fault tests get disabled. Build the former.