The Model Driven Architecture (MDA) is a software design approach initiated by OMG. MDA is intended to support model driven engineering of software systems. Under MDA, the central artifacts are models which are transformed to include platform-specific detail, and eventually to source code. Therefore, model transformations play a key role in making MDA succeed. However, much less attention has been given to the need to ensure that model transformations generate the intended results. This paper explores validation and verification of model transformations using testing techniques. The paper describes the steps for generating test input models from a given set of transformation rules and the corresponding source metamodel(s). The process of testing model transformations has been implemented in a prototype tool that is built using the Eclipse Modeling Framework (EMF).