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SKILL.md
npx skills add giuseppe-trisciuoglio/developer-kit --skill unit-test-mapper-converter
Provides patterns for unit testing mappers, converters, and bean mappings. Validates entity-to-DTO and model transformation logic in isolation. Generates executable mapping tests with MapStruct and custom converter test coverage. Use when writing mapping tests, converter tests, entity mapping tests, or ensuring correct data transformation between DTOs and domain objects.
npx skills add giuseppe-trisciuoglio/developer-kit --skill unit-test-mapper-converter
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.
Before testing, verify generated mapper classes exist:
If generated classes are missing:
mvn compile (Maven) or ./gradlew compileJava (Gradle)@Mapper interfaces are in a compiled source setConfigure nullValueMappingStrategy in mapper if null should return empty/default.
If null tests fail:
nullValueMappingStrategy = NullValueMappingStrategy.RETURN_NULL to @MappernullValuePropertyMappingStrategy for nested property handlingIf bidirectional tests fail:
@Mapping annotations for field name mismatchesunmappedTargetPolicy = ReportingPolicy.ERROR to catch missing mappingsIf nested tests fail:
uses = NestedMapper.classelementMappingStrategyCustom expressions in @Mapping(target = "field", expression = "java(...)") are not compile-time validated.
If expression tests fail:
Use @ValueMapping for enum-to-enum translations. Test all enum values exhaustively.
Mappers.getMapper() for standalone tests, Spring injection for integration testsusingRecursiveComparison() for complex nested structuresnullValueMappingStrategy and nullValuePropertyMappingStrategy appropriately@Mapping are not validated at compile time—test them explicitlyComplete executable test with imports:
Additional examples in: references/examples.md
User restored = mapper.toEntity(mapper.toDto(original));
assertThat(restored).usingRecursiveComparison().isEqualTo(original);assertThat(dto.getNested()).usingRecursiveComparison().isEqualTo(expected);package com.example.mapper;
import org.junit.jupiter.api.Test;
import org.mapstruct.factory.Mappers;
import static org.assertj.core.api.Assertions.*;
class UserMapperCompleteTest {
private final UserMapper mapper = Mappers.getMapper(UserMapper.class);
@Test
void shouldMapUserToDto() {
User user = new User(1L, "Alice", "alice@example.com", 25);
UserDto dto = mapper.toDto(user);
assertThat(dto)
.isNotNull()
.extracting(UserDto::getName, UserDto::getEmail)
.containsExactly("Alice", "alice@example.com");
}
@Test
void shouldMaintainRoundTrip() {
User original = new User(1L, "Alice", "alice@example.com", 25);
assertThat(mapper.toEntity(mapper.toDto(original)))
.usingRecursiveComparison()
.isEqualTo(original);
}
@Test
void shouldHandleNullInput() {
assertThat(mapper.toDto(null)).isNull();
}
}