What is a unit test and why is it important in backend development?

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A unit test is an automated test that verifies the correct behavior of a small, isolated unit of code, typically a function or method. The goal is to validate that a unit produces the expected result for given inputs.

The characteristics of a good unit test are as follows. It is isolated and does not depend on other components like databases or networks. It is fast to execute, usually a few milliseconds. It is repeatable and always gives the same result. It is self-validating, meaning it passes or fails without human intervention.

The importance of unit tests in backend development is significant.

First, they detect bugs early. A bug found during development costs much less to fix than a bug in production.

Second, they facilitate refactoring. When I modify code, tests confirm that I have not broken existing behavior. I can improve the code with confidence.

Third, they serve as documentation. A well-written test shows how to use a function and what behavior to expect. It is living documentation that stays up to date.

Fourth, they improve design. Writing tests pushes you to create modular and decoupled code, because code that is hard to test is often poorly designed code.

In backend development, I prioritize testing business logic, validations, data transformations, and edge cases.