321 Frameworks Spring Boot Testing Unit Tests

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.