131-java-testing-unit-testing
This Claude Code skill reviews and improves Java unit tests by applying modern best practices with JUnit 5, AssertJ, and Mockito. Use it when you need to modernize existing tests, migrate from JUnit 4 to JUnit 5, implement fluent assertions, structure tests with Given-When-Then patterns, add parameterized tests, mock dependencies, verify boundary conditions, or eliminate testing anti-patterns like reflection-based tests and shared mutable state.
git clone --depth 1 https://github.com/jabrena/cursor-rules-java /tmp/131-java-testing-unit-testing && cp -r /tmp/131-java-testing-unit-testing/skills/131-java-testing-unit-testing ~/.claude/skills/131-java-testing-unit-testingSKILL.md
# 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 **Scope:** The reference is organized by examples (good/bad code patterns) for each core area. Apply recommendations based on applicable examples. ## Constraints Before applying any unit test changes, ensure the project compiles. If compilation fails, stop immediately — do not proceed until resolved. After applying improvements, run full verification. - **MANDATORY**: Run `./mvnw compile` or `mvn compile` before applying any change - **SAFETY**: If compilation fails, stop immediately and do not proceed — compilation failure is a blocking condition - **VERIFY**: Run `./mvnw clean verify` or `mvn clean verify` after applying improvements - **BEFORE APPLYING**: Read the reference for detailed examples, good/bad patterns, and constraints ## When to use this skill - Review Java code for unit tests - Apply best practices for unit tests in Java code ## Workflow 1. **Compile project before unit-test changes** Run `./mvnw compile` or `mvn compile` and stop immediately if compilation fails. 2. **Read unit-testing reference and evaluate coverage** Read `references/131-java-testing-unit-testing.md` and identify modernization and quality gaps in current tests. 3. **Apply unit-testing best practices** Implement or refactor tests using JUnit 5, AssertJ, Mockito, parameterization, and stronger boundary checks. 4. **Verify with full build** Run `./mvnw clean verify` or `mvn clean verify` after applying improvements. ## Reference For detailed guidance, examples, and constraints, see [references/131-java-testing-unit-testing.md](references/131-java-testing-unit-testing.md).
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