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How do you know your code actually works? Unit testing answers that by verifying the smallest, isolated pieces of your code automatically.

A unit is the smallest testable piece of an app — usually a single method, function, or class. Unit tests check each piece works in isolation.

This add method on a Calculator class is a perfect unit to test — small, isolated, with one clear job. Run it to see it work.

You could eyeball output by hand, but that’s slow and error-prone across thousands of methods. Automated tests run fast and consistently, every time.

The biggest payoff: catching bugs early. A bug found in development is far cheaper to fix than one in production — your tests are the safety net.

A failing unit test points straight to the misbehaving piece, so you skip hunting through the whole app. That’s easier debugging.

Tests give you confidence to refactor: reshape your code freely, and if you break something, a failing test tells you instantly.

Writing tests nudges you toward better design — testable code has to be modular with clear responsibilities, which means cleaner software overall.

Unit tests are the foundation of your testing strategy — written by developers alongside the code, like checking each brick before you build the wall.

Which of the following is NOT a primary benefit of writing unit tests?

You’ve got the fundamentals: unit tests verify the smallest pieces, run fast and automatically, and bring early bug detection plus safe refactoring. JUnit 5 next!