Unit testing

Unit tests verify small pieces of logic in isolation. Good unit tests are focused, deterministic, readable, and quick to run.

Node.js includes a built-in test runner, which is enough to start testing many small applications without adding another test framework.

Deep dive

What should be tested?

• Normal successful cases.
• Boundary values.
• Invalid input.
• Expected errors.
• Important business rules.

Testing pyramid idea

Keep many fast unit tests, add integration tests for database and service boundaries, and use a smaller number of end-to-end tests for complete user flows.