Theme Regression Testing Strategy

Scope

A layered approach to prevent dark and light mode regressions in production.

Pyramid

• unit: resolution logic and store behavior
• integration: layout application and CSS token usage
• e2e: paint, navigation, and persistence

Unit Cases

• preference precedence matrix
• storage normalization
• media query listener transitions

Integration Cases

• data-theme updates on state changes
• key screens inherit semantic tokens correctly
• contrast utility reports no AA violations

E2E Cases

• first paint is in resolved theme
• no flash when navigating between routes
• multi-tab storage sync works

Tooling

• vitest for store and utility tests
• playwright for visual and behavior checks
• contrast validator in CI gate

Release Gate

Do not ship when:

• any critical theme test fails
• contrast checks fail
• first-paint mismatch detected in smoke tests

Anti-patterns

• relying only on manual QA
• snapshot tests without behavior assertions
• missing tests for system theme changes