During the development of a software system, such as automatic transmission control unit of passenger cars, the developer must check how the system satisfies the requirements from the customers perspective. At the customer side, reliability and correctness are the most important factors in terms of the product quality. In order to achieve a certain degree of these quality factors, the adequate development methods or standards must be applied during the whole development process of the product. Testing is the most important activity of the development process to assess the product reliability and correctness. In this paper the real-time statistical-based test environment is presented. The objective is to assess the quality of automatic transmission control unit of passenger cars in its intended environment applying a usage profile.