Provides patterns for unit testing service layer with Mockito. Creates isolated tests that mock repository calls, verify method invocations, test exception…
Isolated unit testing patterns for Spring service layer using Mockito and JUnit 5. Covers mocking injected dependencies, verifying service interactions, and testing business logic without database or external API calls Includes patterns for exception handling, complex workflows, argument capturing, and verification of call order and frequency Supports testing async/reactive services with CompletableFuture and provides best practices for constructor injection and spy-based partial mocking Demonstrates common anti-patterns to avoid and troubleshooting guidance for typical Mockito and JUnit 5 issues Unit Testing Service Layer with Mockito Overview 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. When to Use Testing business logic in @Service classes Mocking repository and external client dependencies Verifying service interactions with mocked collaborators Testing error handling and edge cases in services Writing fast, isolated unit tests (no database, no API calls) Instructions Follow this workflow to test service layer with Mockito, including validation checkpoints: 1. Setup Test Class
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