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:

# 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

assertThat(mapper.toDto(null)).isNull();

Configure nullValueMappingStrategy in mapper if null should return empty/default.