unit-test-service-layer
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
@Serviceclasses - 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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