Test Layer Rules

About

Test Layer Rules define guidelines for organizing, writing, and structuring unit, integration, and functional tests in a Spring project. Proper test layer rules ensure that tests are maintainable, reliable, and clearly separated from production code.

In Spring applications, the test layer typically includes:

• Unit Tests: Focused on individual classes or methods using mocks.

• Integration Tests: Validate interactions between multiple components or layers.

• Functional / End-to-End Tests: Validate complete workflows, often using Spring Boot test utilities or mock servers.

By enforcing test layer rules, teams can maintain high code quality and avoid mixing test concerns with production code.

Purpose

The purpose of Test Layer Rules is to ensure that testing in a Spring project is structured, effective, and maintainable, while keeping test code separate from production code.

Key objectives include:

1. Maintain clear separation of concerns

   • Tests should reside in dedicated test packages (src/test/java) and mirror the production package structure.

2. Ensure reliability and consistency

   • Proper layering of unit, integration, and functional tests ensures predictable and reproducible results.

3. Facilitate maintainability and refactoring

   • Well-structured tests allow developers to safely modify production code without breaking unrelated functionality.

4. Enable automated enforcement

   • Test coverage, naming conventions, and dependency rules can be enforced via CI/CD pipelines.

5. Promote team collaboration

   • Consistent test organization helps new developers understand the testing strategy and locate relevant tests quickly.

Rules

1. Package Structure

• Test classes should mirror the production package structure.

  • Example: com.company.employeeportal.service.EmployeeService → com.company.employeeportal.service.EmployeeServiceTest

• Separate packages for unit, integration, and functional tests can be created if needed.

2. Naming Conventions

• Unit test classes should end with Test.

  • Example: EmployeeServiceTest

• Integration test classes can end with IT (Integration Test).

  • Example: EmployeeServiceIT

• Functional / End-to-End tests can use descriptive suffixes like E2ETest.

3. Annotations

• Use Spring testing annotations appropriately:

  • @SpringBootTest for full application context tests.

  • @WebMvcTest for controller-layer tests.

  • @DataJpaTest for repository-layer tests.

  • @MockBean and @Autowired for dependency injection in tests.

4. Dependency Rules

• Test classes may depend on:

  • Production classes under test.

  • Mocks, test utilities, DTOs, and entities.

5. Test Method Conventions

• Methods should use descriptive names using camelCase, clearly indicating the scenario.

  • Example: createEmployee_shouldReturnSavedEmployee_whenValidDataProvided()

• Each test should verify a single behavior (unit principle).

6. Test Isolation

• Unit tests should not depend on external services or databases; use mocks or in-memory replacements.

• Integration tests may connect to test databases or mock servers, but ensure isolation per test.

7. Avoid Test Pollution

• Do not modify shared static data across tests unless properly reset.

• Ensure idempotent tests that can run independently and in parallel.

8. Utilities and Helpers

• Shared test utilities or mock data providers can reside in a util subpackage under src/test/java.

• Avoid placing production logic in test utilities.