unit-test-service-layer

Isolated unit testing patterns for Spring service layer using Mockito and JUnit 5. Provides patterns for unit testing @Service classes using Mockito. Mocks repository calls, verifies method invocations, tests exception scenarios, and stubs external API responses. Enables fast, isolated tests without Spring container or database. Follow this workflow to test service layer with Mockito, including validation checkpoints: Use @ExtendWith(MockitoExtension.class) to enable Mockito annotations. Use @Mock for dependencies (repositories, clients) and @InjectMocks for the service under test. Arrange : Create test data and configure mock return values using when().thenReturn() . Act : Execute the service method being tested.