131 Java Testing Unit Testing

This is a comprehensive testing modernizer for Java projects. It walks you through migrating from JUnit 4 to JUnit 5, switching to AssertJ's fluent assertions, and applying proper test structure with Given-When-Then. What's useful here is the safety-first approach: it forces you to compile before making changes and verify afterward, which prevents breaking your build mid-refactor. The skill covers the full testing stack including Mockito mocking, parameterized tests, and boundary condition verification using RIGHT-BICEP and CORRECT principles. It's built for teams trying to eliminate common anti-patterns like reflection-based tests and shared mutable state while adopting modern practices like JSpecify null-safety annotations.

skills.sh installs: 134
GitHub stars: 393
last updated: Jun 3, 2026

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Install

$ npx -y skills add jabrena/cursor-rules-java --skill 131-java-testing-unit-testing --agent claude-code

Installs into .claude/skills of the current project.

Files

Java Unit testing guidelines

Review and improve Java unit tests using modern JUnit 5, AssertJ, and Mockito best practices.

What is covered in this Skill?

JUnit 5 annotations: @Test, @BeforeEach, @AfterEach, @DisplayName, @Nested, @ParameterizedTest
AssertJ fluent assertions: assertThat, assertThatThrownBy
Given-When-Then test structure, descriptive test naming, single-responsibility tests
Test independence and isolated state
Parameterized tests: @ValueSource/@CsvSource/@MethodSource
Mockito dependency mocking: @Mock, @InjectMocks, MockitoExtension
Code coverage guidance (JaCoCo), package-private test visibility
Testing anti-patterns: reflection, shared state, hard-coded values, testing implementation details
Error handling: assertThatThrownBy, exception messages
JSpecify null-safety: @NullMarked, @Nullable
RIGHT-BICEP coverage principles, A-TRIP test quality, CORRECT boundary condition verification