Testing is one of those things that everyone knows they should do, but it's easy to put off. When you're building features, writing tests feels like extra work. But I've learned that good tests save time in the long run. They catch bugs before they reach production, and they give you confidence to refactor code.

Testing can be overwhelming because there are so many types: unit tests, integration tests, end-to-end tests, and more. It's not always clear what to test or how to test it. But you don't need to test everything perfectly from the start. Start with the basics and build from there.

Why testing matters

Tests serve as documentation. When you read a test, you can see how code is supposed to work. Tests show what inputs are expected and what outputs should be produced. This is especially valuable when you come back to code months later.

Tests also make refactoring safer. When you need to change code, tests tell you if you've broken anything. Without tests, you're afraid to change code because you don't know what might break.

Good tests catch bugs before they reach users. It's much cheaper to fix a bug during development than after it's in production. Tests help you catch these bugs early.

Unit testing

Unit tests test individual functions or components in isolation. They're fast to run and easy to write. Unit tests should test one thing at a time and be independent of each other.

For backend code, unit tests might test a function that processes data or validates input. You test the function with different inputs and verify it produces the expected outputs.

For frontend code, unit tests might test a React component. You render the component with different props and verify it displays correctly or handles interactions properly.

Unit tests are the foundation of your test suite. They're quick to write and run, so you can have many of them. They catch most bugs and give you fast feedback during development.

Integration testing

Integration tests test how different parts of your application work together. They might test how your API endpoints interact with your database, or how multiple components work together in a React application.

Integration tests are slower than unit tests because they involve more of your application. But they catch bugs that unit tests miss—bugs that happen when different parts interact.

For APIs, integration tests might test an endpoint end-to-end: make a request, verify the database is updated correctly, and check the response. This tests the API, the database interaction, and the business logic together.

End-to-end testing

End-to-end tests test your entire application from a user's perspective. They simulate a user interacting with your application through a browser. These tests are the slowest but catch the most realistic bugs.

End-to-end tests are valuable but expensive. They're slow to run and can be flaky. Use them sparingly for critical user flows. Don't try to test everything with end-to-end tests—that's what unit and integration tests are for.

Tools like Cypress or Playwright make end-to-end testing easier. They provide good APIs for interacting with browsers and waiting for elements to appear.

Testing frontend code

For React applications, testing libraries like React Testing Library make it easy to test components. You render components, query for elements, and simulate user interactions. The library encourages testing from a user's perspective rather than testing implementation details.

Focus on testing behavior, not implementation. Test that clicking a button does what the user expects, not that a specific function was called. This makes tests more resilient to refactoring.

Mock external dependencies like API calls. You don't want your tests to make real API calls—they should be fast and independent. Use mocking libraries to simulate API responses.

Testing backend code

For backend code, test your business logic thoroughly. Test edge cases, error conditions, and different input scenarios. Make sure your validation works, your data processing is correct, and your error handling is appropriate.

Mock your database in unit tests. You don't want tests to depend on a real database—they should be fast and independent. Use in-memory databases or mocks for unit tests.

Use a test database for integration tests. This lets you test real database interactions while keeping tests isolated. Make sure to clean up test data between tests.

Test organization

Organize your tests to match your code structure. If you have a utils folder, have a utils test folder. This makes it easy to find tests for specific code.

Use descriptive test names that explain what you're testing. A test name like "should return error when email is invalid" is much better than "test email validation."

Keep tests simple and focused. Each test should test one thing. If a test is long and complex, break it into multiple tests.

Coverage

Test coverage measures what percentage of your code is executed by tests. It's a useful metric, but don't obsess over it. 100% coverage doesn't mean your code is well-tested—you might be testing the wrong things.

Aim for good coverage of critical paths. Focus on testing code that's important and likely to have bugs. Don't waste time testing simple getters and setters.

The bottom line

Testing is an investment that pays off over time. Start with unit tests for critical functionality, add integration tests for important flows, and use end-to-end tests sparingly for critical user journeys.

Don't try to test everything perfectly from the start. Start simple, learn what works for your application, and improve your testing strategy over time. Good tests make development faster and more enjoyable, not slower.