Best Practices for Writing Unit Tests in Spring Boot

Writing effective unit tests makes your code more reliable and easier to maintain. Follow these best practices to create clear, maintainable, and meaningful unit tests in your Spring Boot applications.

Organizing Your Tests

• Group test classes in a dedicated src/test/java directory;
• Mirror your main application package structure for test classes;
• Place each test class in the same package as the class it tests;
• Use descriptive folder and file names to clarify what each test covers.

Naming Conventions

• Name test classes after the class being tested, adding Test at the end (such as UserServiceTest);
• Name test methods to describe exactly what they check, using the format methodName_StateUnderTest_ExpectedBehavior (such as createUser_WithValidInput_ReturnsSavedUser);
• Avoid vague method names like test1 or testUser.

Test Coverage

• Write tests for all public methods and important logic branches;
• Focus on edge cases and typical usage scenarios;
• Avoid testing private methods directly; instead, test them through public interfaces.

Using Mocks Effectively

• Use the @MockBean annotation to replace dependencies with mocks in your test class;
• Mock only external dependencies, such as repositories or external services, not the class under test;
• Use the when...thenReturn pattern from Mockito to define mock behavior;
• Verify interactions with mocks using verify to ensure correct usage.

Additional Tips

• Keep tests independent; do not rely on the order of execution;
• Use clear, meaningful assertions to make test outcomes obvious;
• Clean up any test data or mocks after each test if needed;
• Run tests frequently to catch issues early.

Following these best practices helps you build a robust, maintainable test suite that makes your Spring Boot application easier to develop and refactor.