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This comprehensive JUnit guide takes you from unit testing basics to advanced testing patterns, covering everything Java developers need to master JUnit 5 and write effective, maintainable tests.
1 - JUnit Fundamentals
Getting started with unit testing
1. Introduction to JUnit
What is JUnit, history, JUnit 5 architecture
2. Setup and Installation
Maven, Gradle, IDE configuration
3. Writing Your First Test
Basic test structure and execution
2 - Annotations & Assertions
Core testing features and assertions
1. JUnit Annotations
@Test, @BeforeEach, @AfterEach, @DisplayName
2. Assertions Deep Dive
Assertions API, custom messages, soft assertions
3. Assumptions & Conditional Testing
@Disabled, assumeThat, conditional execution
3 - Test Lifecycle
Test setup, teardown, and execution
1. Test Lifecycle Hooks
@BeforeAll, @AfterAll, @BeforeEach, @AfterEach
2. Test Instances & Execution Order
Test instance lifecycle, @TestMethodOrder
3. Nested Tests & Test Classes
@Nested, test organization, inner test classes
4 - Advanced Testing
Parameterized and dynamic tests
1. Parameterized Tests
@ParameterizedTest, value sources, argument providers
2. Dynamic Tests
@TestFactory, runtime test generation
3. Repeated Tests & Templates
@RepeatedTest, @TestTemplate, test templates
5 - Extensions & Integration
JUnit extensions and tool integration
1. JUnit Extensions
Extension API, custom extensions, lifecycle callbacks
2. Mocking with Mockito
@Mock, @InjectMocks, Mockito integration
3. Spring Test Integration
@SpringBootTest, @WebMvcTest, test slices
6 - Best Practices
Testing patterns and best practices
1. Test Naming & Organization
Naming conventions, test structure, AAA pattern
2. Test Coverage & Quality
Code coverage, test quality metrics, JaCoCo
3. Testing Anti-patterns
Common mistakes, what to avoid, refactoring tests
7 - Real-world Applications
Practical testing scenarios
1. Testing REST APIs
Controller testing, MockMvc, API validation
2. Testing Database Operations
@DataJpaTest, @Sql, testcontainers
3. Performance & Load Testing
@Timeout, performance assertions, JMH integration
Prerequisites
- Java 8+ knowledge
- Understanding of unit testing concepts
- Basic familiarity with Java development tools (Maven or Gradle)
- Experience with an IDE (IntelliJ IDEA, Eclipse, or VS Code)
- Optional: Spring Boot familiarity for integration sections
JUnit Concepts
@Test
Assertions
@BeforeEach
@AfterEach
@ParameterizedTest
@Nested
@RepeatedTest
@TestFactory
Extensions
Mockito
@SpringBootTest
TestContainers
JaCoCo
@DisplayName
Assumptions
JUnit main concepts covered in this learning path
Each post will contain practical examples, code samples, and hands-on exercises to help you master JUnit from basics to advanced testing patterns and real-world applications.
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