unit-test-mapper-converter

# Unit Testing Mappers and Converters ## Overview Provides patterns for unit testing MapStruct mappers and custom converter classes. Covers field mapping accuracy, null handling, type conversions, nested object transformations, bidirectional mapping, enum mapping, and partial updates. ## When to Use - Writing mapping tests for MapStruct mapper implementations - Testing custom entity-to-DTO converters and bean mappings - Validating nested object mapping and collection transformations ## Instructions ### 1. Validate Generated Mapper Classes Before testing, verify generated mapper classes exist: ```bash # Maven ls target/generated-sources/ # Gradle ls build/generated/sources/ ``` **If generated classes are missing:** 1. Run `mvn compile` (Maven) or `./gradlew compileJava` (Gradle) 2. Check that the MapStruct annotation processor is configured 3. Verify `@Mapper` interfaces are in a compiled source set ### 2. Test Null Handling ```java assertThat(mapper.toDto(null)).isNull(); ``` Configure `nullValueMappingStrategy` in mapper if null should return empty/default. **If null tests fail:** 1. Add `nullValueMappingStrategy = NullValueMappingStrategy.RETURN_NULL` to `@Mapper` 2. Or use `nullValuePropertyMappingStrategy` for nested property handling ### 3. Test Bidirectional Mapping ```java User restored = mapper.toEntity(mapper.toDto(original)); assertThat(restored).usingRecursiveComparison().isEqualTo(original); ``` **If bidirectional tests fail:** 1. Check `@Mapping` anno...