Today, test suites of several ten thousand lines of code are specified using the Testing and Test Control Notation (TTCN-3). Experience shows that the resulting test suites suffer from quality problems with respect to internal quality aspects like usability, maintainability, or reusability. Therefore, a quality assessment of TTCN-3 test suites is desirable. A powerful approach to detect quality problems in source code is the identification of code smells. Code smells are patterns of inappropriate language usage that is error-prone or may lead to quality problems. This paper presents a quality assessment approach for TTCN-3 test suites which is based on TTCN-3 code smells: To this aim, various TTCN-3 code smells have been identified and collected in a catalogue; the detection of instances of TTCN-3 code smells in test suites has been automated by a tool. The applicability of this approach is demonstrated by providing results from the quality assessment of several standardised TTCN-3 test suites.