analyzing-test-coverage

Test coverage analysis with Vitest involves running tests with the --coverage flag to measure code execution, then interpreting results to identify untested branches. Use pnpm test --coverage to generate coverage reports and identify gaps in your unit, integration, and end-to-end tests.

Organize Vitest tests by layer: service tests mock dependencies with vi.mock and vi.fn, repository tests use fixtures, and integration tests use MSW to mock network interactions. This layered structure ensures consistent coverage across unit, integration, and E2E workflows.

Test data builders provide fluent, reusable fixtures to generate consistent test objects across unit and integration tests. Builders reduce duplication, improve maintainability, and ensure test data evolves with your domain models.

MSW integrates with Vitest to mock HTTP requests at the network level, enabling reliable integration and end-to-end tests without external dependencies. Configure MSW handlers in your test setup to intercept and respond to network calls consistently.

Layered test organization clarifies dependencies and test scope: service tests verify business logic, repository tests validate data access patterns, and integration tests confirm components work together. This structure improves test clarity and coverage accuracy.

Use vi.fn for spy assertions and return values on isolated functions, and vi.mock for module-level replacements in service tests. Combine both patterns with test builders to create predictable, verifiable test scenarios across your Vitest suite.