spring-boot-testing

name	spring-boot-testing
description	Use this skill when writing or improving tests in a Spring Boot project, including unit tests, integration tests, and test structure.

Spring Boot Testing

Scope

Apply this skill when working on:

• unit tests for services and components
• integration tests for Spring Boot applications
• controller tests
• improving test coverage and quality

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Testing philosophy

• Write meaningful, maintainable tests.
• Focus on behavior, not implementation details.
• Cover both happy paths and edge cases.
• Keep tests deterministic and isolated.

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Frameworks

• Use JUnit 5 (Jupiter).
• Prefer AssertJ for assertions.

assertThat(result)
    .isNotNull()
    .hasFieldOrPropertyWithValue("status", "ACTIVE");

Test types and strategy

Use the appropriate test type based on scope:

Unit tests

• Test service and utility logic in isolation.
• Do not start Spring context.
• Use mocks (e.g., Mockito) for dependencies.

Slice tests (recommended for most cases)

• Load only a part of the Spring context.
• Prefer slice tests as the default testing approach in Spring Boot applications.

Common slices:

• @WebMvcTest → controller layer
• @DataJpaTest → repository layer

Benefits:

• faster than full context
• focused and isolated

Integration tests

• Use @SpringBootTest when:
  • testing full application behavior
  • verifying configuration and wiring
• Combine with:
  • @AutoConfigureMockMvc for API testing
  • Testcontainers for real database testing

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Test isolation and data

• Prefer in-memory or containerized databases for tests.
• Reset state between tests.
• Avoid shared mutable state.
• Keep tests deterministic and repeatable.

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What to prefer

• Prefer slice tests over full @SpringBootTest where possible.
• Use full context tests only when necessary.
• Keep test execution fast to support frequent runs.