Testing Test Writing

Unit tests should target core business logic and primary functionality at logical completion points. Identify the critical paths in your code—the workflows users depend on—and write tests for those first, mocking external dependencies to keep tests fast and isolated. This strategic approach prevents brittle test suites while ensuring essential features work correctly.

Unit tests verify individual functions in isolation; integration tests check how components work together; end-to-end tests simulate complete user workflows. Strategic test writing uses all three: unit tests for business logic, integration tests for component interactions, and E2E tests for critical user flows like checkout or registration. Each layer serves a different purpose in covering core functionality.

Replace external services—like payment gateways or APIs—with mock objects that return predefined responses. This isolates your code, speeds up test execution, and lets you test error scenarios without hitting real services. Mocking ensures tests are reliable and fast while focusing on testing your application's behavior, not third-party systems.

Testing behavior means verifying what your code does from the user's perspective, not how it does it. When you test implementation details, refactoring breaks tests even though the feature still works. Behavioral tests remain stable across code changes and catch real bugs that affect users, making your test suite more maintainable and trustworthy.

Create files with naming patterns like `*.test.ts`, `*.spec.ts`, `*.test.js`, or place them in a `__tests__` directory. Most test runners automatically discover tests in these locations. Name tests descriptively to document what each test verifies, making the test suite self-explanatory and easier to maintain as your codebase grows.

Too few tests leave critical paths uncovered; too many slow your suite and become maintenance burden. Strategic testing focuses on core user flows and essential features. If you're testing every helper function or implementation detail, you're likely over-testing. Instead, verify that happy paths work and key error scenarios are handled.