In this article we are focusing on interoperability of two aspects of LMS systems - test question types and assessments as such. The proposed strategy is based on MDA, especially on the Platform Independent Models (PIM). On the higher level of abstraction (PIM) it is possible to find commonalities and differences of architectures of various systems and these are the basis for the common generalized model of the assessments. In the three steps methodology we are adding specificities of PIM models of candidate systems with various architecture – Moodle, Olat and Claroline. The correctness of the final common model (General PIM) is proved in the implemented system for exchange of tests between the existing systems.