The expansion and the importance of testing in today's automobile industry sector is unquestionable. As testing has both significant economic and security aspects, producers tend to put an increasing emphasis on it. The testing process initiates as soon as the parts of the vehicle are being produced, to secure full individual checking. There are multiple options to come up with an equipment suitable for testing the units of an automobile, one of them, a miniature, inexpensive mobile handheld tester, is capable of communicating with each unit through the communicational bus of the vehicle. Throughout the testing process, we carry out simulations, with which we seek to uncover informations about various setups of the parameters of the given unit. For such a mobile testing unit, the design and size of the user interface is utterly important, in order to keep the tool as simple as possible. This thesis deals with the development of the user interface and the graphical menu of such a testing unit. The hardware and software development of the prototype, necessary background informations about underlying technologies, and a step-by-step description of the development process are all being introduced and sufficiently detailed.