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java-junit

Write JUnit 5 unit tests with parameterized tests, assertions, and Mockito mocking.

Updated Dec 26, 2025
Search Tags:#unit testing#java#maven#junit#mockito#assertj#parameterized tests
One-click install
npx skills add https://github.com/jwvdvuurst/CalculatorCollection --skill java-junit-jwvdvuurst
Or copy as Structured Prompt for Agent▼
Please help me install this Agent Skill.
Skill: java-junit
Source: https://github.com/jwvdvuurst/CalculatorCollection/tree/main/skills/java-junit
Command: npx skills add https://github.com/jwvdvuurst/CalculatorCollection --skill java-junit-jwvdvuurst

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve? Writing consistent, maintainable unit tests in Java requires knowing JUnit 5 conventions, parameterized test sources, assertion patterns, and mocking setup, which developers often get wrong or apply inconsistently. ## Core Features & Use Cases - Test Structure Guidance: Enforces AAA pattern, naming conventions, lifecycle annotations like @BeforeEach, and @DisplayName usage. - Data-Driven Testing: Covers @ParameterizedTest with @ValueSource, @MethodSource, @CsvSource, @CsvFileSource, and @EnumSource. - Assertions & Mocking: Recommends Assertions static methods, AssertJ fluent assertions, assertThrows, assertAll, and Mockito with @Mock and @InjectMocks. - Use Case: When adding tests for a new Calculator service class, generate a CalculatorTest with parameterized cases for edge inputs and mocked dependencies. ## Quick Start Write JUnit 5 tests for my Calculator class including parameterized tests for the divide method and a Mockito mock for its repository dependency.

Frequently Asked Questions about java-junit

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I write parameterized tests in JUnit 5?▼

Use @ParameterizedTest with a source annotation: @ValueSource for literals, @CsvSource for inline comma-separated values, @MethodSource for a factory method returning a Stream, or @CsvFileSource for classpath CSV files. Add junit-jupiter-params to your dependencies.

How to mock dependencies in JUnit 5 with Mockito?▼

Annotate dependencies with @Mock and the class under test with @InjectMocks so Mockito creates and injects mocks automatically. Coding to interfaces makes mocking easier and keeps tests isolated from real implementations.

What is the difference between @BeforeEach and @BeforeAll in JUnit 5?▼

@BeforeEach runs before every test method for per-test setup, while @BeforeAll runs once per class and must be a static method. Use @AfterEach and @AfterAll for the corresponding teardown logic.

Should I use JUnit assertions or AssertJ?▼

JUnit's org.junit.jupiter.api.Assertions covers standard checks like assertEquals, assertThrows, and assertAll. AssertJ provides fluent, more readable assertions like assertThat(x).isEqualTo(y) and is recommended when readability matters.

How do I run JUnit 5 tests with Maven or Gradle?▼

Place tests in src/test/java with a Test suffix on class names, then run mvn test for Maven or gradle test for Gradle. Ensure junit-jupiter-api and junit-jupiter-engine are declared as test dependencies.

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