Spring Boot Unit Testing with Mockito
Apply Spring Boot unit testing guidelines with Mockito.
What is covered in this Skill?
- Pure unit tests: @ExtendWith(MockitoExtension.class), @Mock, @InjectMocks for @Service/@Component (no Spring context)
- Slice tests: @WebMvcTest, @MockitoBean for controllers (Spring Boot 4.0.x — @MockBean removed)
- @JsonTest for JSON serialization with correct JSON value assertions (extractingJsonPathStringValue, etc.)
- Parameterized tests: @ParameterizedTest with @CsvSource or @MethodSource over copy-pasted methods
- Java records for domain objects in tests
- @TestConfiguration, @ActiveProfiles, @Primary fixed-clock beans for deterministic test setup
- Modern mocking API: @MockitoBean / @MockitoSpyBean; @MockBean/@SpyBean are deprecated/removed in Boot 4.0.x
Scope: Apply recommendations based on the reference rules and good/bad code examples. For integration tests use @322-frameworks-spring-boot-testing-integration-tests.
Constraints
Before applying any test changes, ensure the project compiles. If compilation fails, stop immediately. After applying improvements, run full verification.
- MANDATORY: Run
./mvnw compile or mvn compile before applying any change
- SAFETY: If compilation fails, stop immediately
- VERIFY: Run
./mvnw clean verify or mvn clean verify after applying improvements
- BEFORE APPLYING: Read the reference for detailed rules and good/bad patterns
- EDGE CASE: If request scope is ambiguous, stop and ask a clarifying question before applying changes
- EDGE CASE: If required inputs, files, or tooling are missing, report what is missing and ask whether to proceed with setup guidance
When to use this skill
- Review Java code for Spring Boot unit tests
- Apply best practices for Spring Boot unit tests in Java code
- Write Mockito-first unit tests for Spring Boot services
- Avoid unnecessary @SpringBootTest in Spring unit tests
- Review Spring Boot slice-free unit test design
Workflow
- Read reference and assess project context
Read references/321-frameworks-spring-boot-testing-unit-tests.md and inspect the current project setup before proposing changes.
- Gather scope and decide target improvements
Identify requested outcomes, constraints, and the minimum safe set of changes to apply.
- Apply framework-aligned changes
Implement or refactor configuration/code following the reference patterns and project conventions.
- Run verification and report results
Execute appropriate build/tests and summarize what changed, what was verified, and any follow-up actions.
Reference
For detailed guidance, examples, and constraints, see references/321-frameworks-spring-boot-testing-unit-tests.md.