testing

Type tests validate that your TypeScript types infer correctly at compile time using assertions from libraries like inferred-types. They catch type errors before runtime by checking generic resolution, literal type narrowing, and type inference behavior, complementing runtime tests for complete code quality coverage.

Use runtime tests with Vitest to validate behavior and side effects; use type tests to verify type inference and generic constraints at compile time. TDD guides this decision: write type tests for type-level contracts and runtime tests for functional requirements, ensuring both layers are tested.

Organize tests by writing them before implementation, grouping runtime tests by feature and type tests by type assertion. Use test commands and CI integration to run both suites automatically, ensuring tests are maintainable, discoverable, and enforced in your development workflow.

Vitest handles runtime tests effectively. Pair it with inferred-types for type testing to validate compile-time type correctness. Together they provide comprehensive coverage: Vitest tests behavior, while type assertions verify that generics and type inference work as intended.

Avoid separating type assertions into isolated blocks, using runtime checks to validate types, or forgetting to export tested types. Type tests must remain adjacent to the code they validate and use proper type assertion syntax to catch inference failures at compile time, not runtime.

Configure test commands in your build tooling to run both runtime and type tests automatically. Integrate into CI pipelines so tests execute on every commit, catching regressions early and enforcing quality standards before code reaches production.