Quality models are needed to evaluate and set goals for the quality of a software product. The international ISO/IEC standard 9126 defines a general quality model for software products. Software is developed in different domains and the usage of the ISO/IEC quality model requires an instantiation for each concrete domain. One special domain is the development and maintenance of test specifications. Test specifications for testing, e.g. the Internet Protocol version 6 (IPv6) or the Session Initiation Protocol (SIP), reach sizes of more than 40.000 lines of test code. Such large test specifications require strict quality assurance. In this paper, we present an adaptation of the ISO/IEC 9126 quality model to test specifications and show its instantiation for test specifications written in the Testing and Test Control Notation (TTCN-3). Example measurements of the standardised SIP test suite demonstrate the applicability of our approach.