The system of computer-aided test development is proposed in the article. The system operation is based on the model of digital device, also system allows to form test as a set of input actions and reactions of model to them. The technology for creating and debugging of tests provides a predetermined test coverage. Input actions are formed according to the interface approach. The interface approach allows to work with the model of digital device at the transaction level, but not at the signal level. This method greatly simplifies and accelerates the process of searching for test sequences. The proposed system structure supports the suggested technology and implements search of test sequences with a predetermined coverage criterion. The developed methodology allows to create a test check programs and diagnostics test program of the digital device, without any information about the destination and operation algorithm of a control object. The system checks the digital device serviceability and its operational suitability.