In the automotive industry, as the complexity of electronic control units (ECUs) increase, there is a need for the creation of models that facilitate early tests to ensure functionality, but there is little guidance on how to write these tests in order to achieve maximum coverage. Our prototype CANoe+, which builds on the CANoe and GraphWalker tools, was evaluated against CANoe with regard to coverage maximization of generated test cases from the viewpoint of both software developers and software testers.