type-checking-vs-testing

Type checking validates static code properties at compile time, while unit testing verifies runtime behavior and logic. Distinguishing type checking versus unit testing prevents over-reliance on one approach and clarifies how they complement each other across JavaScript projects.

Choose type checking to enforce structural integrity and catch regressions, and apply unit tests to validate runtime logic. A practical decision framework evaluates refactoring scope to determine when static types suffice and when robust runtime tests are required.

Yes, strict type checking does not replace unit tests. Types catch structural errors at compile time, but unit tests are required to verify runtime behavior, edge-case handling, and execution logic that static type systems cannot validate.

Prefer type checking for edge cases involving invalid data shapes or null values, as types enforce constraints at compile time. Use unit tests for edge cases involving runtime logic, state transitions, or specific algorithmic outputs.

Integrate type checks into CI by running static analysis during build, while maintaining robust runtime tests in your test suite. This dual approach validates compile-time structural integrity and runtime behavior during refactoring.