Enforce test coverage in development

Enforce test-first development with 80%+ coverage

When test-first discipline and 80%+ coverage must be enforced before merge.

• · feature scope, edge cases to cover, domain model

• · test suite with coverage metrics and passing unit/integration/E2E tests

• · Jest/Vitest test runner, code coverage tools

• · Tests depending on each other
• · Implementation details tested instead of behavior
• · Coverage ceiling hit without edge cases

• · Red-Green-Refactor cycle enforcement
• · Edge case taxonomy
• · Coverage ceiling strategy