congiuluc/testing-backend-java

Backend Testing (Java)

When to Use

• Creating unit tests for services, validators, or domain logic
• Writing integration tests for REST controllers
• Mocking repository or external service dependencies
• Testing Spring Boot configuration and filters

Official Documentation

• JUnit 5 User Guide
• Mockito
• AssertJ
• Spring Boot Testing
• Testcontainers

Core Rule

Every feature must have corresponding tests before it is considered complete.

Procedure

1. Identify test type: unit test (service logic) or integration test (controller endpoint)
2. Follow naming conventions in Java testing reference
3. Review service test sample
4. Use Given-When-Then or Arrange-Act-Assert pattern for all tests
5. Mock external dependencies at boundaries with Mockito
6. Use AssertJ for readable assertions
7. Cover: happy path, edge cases, error scenarios, validation
8. Verify tests are deterministic — no external service or time dependencies
9. Run mvn test or gradle test locally before committing

Test Structure

src/test/java/
  com/myapp/
    domain/             # Domain model unit tests
    application/
      service/          # Service unit tests
    infrastructure/
      persistence/      # Repository adapter tests
    api/
      controller/       # Controller integration tests

Naming Convention

• Test class: {ClassUnderTest}Test (e.g., ProductServiceTest)
• Test method: shouldDoX_whenCondition (e.g., shouldReturnProduct_whenIdExists)