In this paper we present a test-driven approach to porting code from one object-oriented language to another. We derive an order for the porting of the code, along with a testing strategy to verify the behaviour of the ported system at intra and inter-class level. We utilise the recently defined methodology for porting C++ applications, eXtreme porting, as a framework for porting. This defines a systematic routine based upon porting and unit-testing classes in turn. We augment this approach by using Object Relation Diagrams to define an order for porting that minimises class stubbing. Since our strategy is class-oriented and test-driven, we can ensure the structural equivalence of the ported system, along with the limited behavioural equivalence of each class. In order to extend this to integration-level equivalence, we exploit aspect-oriented programming to generate UML sequence diagrams, and we present a technique to compare such automatically-generated diagrams for equivalence. We demonstrate and evaluate our approach using a case study that involves porting an application from C++ to Java.