# JUnit and Mockito

You opened a Java repo, saw a `src/test/java` folder full of `@Test` methods and `mock(...)` calls, and felt the familiar dread: which annotation does what, why is half the test setting up fake objects, and how do you write one of these yourself without copy-pasting the rest of the suite. This guide gives you the two tools that 90% of Java test code is built from, and the mental model to use them without drowning in mocks.

## How to read this

Read the phases in order. Phase 1 builds the JUnit 5 mental model so the annotations stop being noise. Phase 2 puts Mockito next to it and shows the everyday isolate-the-unit workflow. Phase 3 is the part nobody warns you about: the ways these tools quietly lie to you, and how to keep your tests trustworthy. If you've never written a unit test at all, /guides/your-first-unit-test is the gentler on-ramp; come back here for the Java specifics.

## The phases

1. [What JUnit 5 actually is](01-what-junit-5-actually-is.md) - the Jupiter model, `@Test`, lifecycle, and assertions.
2. [Mocking with Mockito](02-mocking-with-mockito.md) - isolate the unit, stub collaborators, verify interactions.
3. [When tests lie](03-when-tests-lie.md) - the mock-too-much trap, brittle verification, and production reality.