unit-test-mapper-converter

Obtain the mapper instance with Mappers.getMapper() for standalone tests, then assert field mappings with AssertJ. Test null inputs, bidirectional round-trips using usingRecursiveComparison(), and verify generated classes exist in target/generated-sources after compilation.

Map an entity to its DTO and back, then compare the restored object to the original using AssertJ's usingRecursiveComparison(). Set unmappedTargetPolicy = ReportingPolicy.ERROR on the @Mapper annotation to catch missing field mappings at compile time.

Generated classes appear only after compilation. Run mvn compile or ./gradlew compileJava, verify the MapStruct annotation processor is configured in your build, and confirm the @Mapper interfaces are in a compiled source set.

No, expressions like @Mapping(target = "field", expression = "java(...)") are not compile-time validated. Test them explicitly by asserting the computed output values, and verify imported classes are accessible from the expression context.

Write a test per mapped value asserting the expected target enum, plus an exhaustive test iterating over all source enum values with values() to confirm none map to null. This catches unmapped constants when new enum values are added.

MapStruct cannot handle circular dependencies between mappers, and immutable collections may need special configuration. Date and time mappings should be verified across timezones, and null handling depends on the configured nullValueMappingStrategy.