We report on the formal development of a test oracle for an electronic-voting system, detailing our approach which was based on a lightweight integration of Event-B, UML, and Java. This lightweight integration focuses on a coherent development process rather than on formal integration at the model/language level. We then briefly review alternative development approaches involving the use of JML and OCL. We conclude that the use of the OCL would offer few benefits, if any, in our formal development process.