Systematic testing is very important for assessing and improving the quality of software systems. Yet, testing turns out to be expensive, laborious, time-consuming and error-prone. The Dutch research and development project C^ote de Resyste worked on methods, techniques and tools for automating specification based testing using formal methods. The main achievement of the project is a test tool, baptized TorX, which integrates automatic test generation, test execution, and test analysis in an on-the-fly manner. On the one hand, TorX is based on well-defined theory, viz. the IOCO-test theory, which has its roots in the theory of testing- and refusal-equivalences for transition systems. On the other hand, the applicability of TorX has been demonstrated by testing several academic and industrial case studies. This paper summarizes the main results of the project C^ote de Resyste. Keywords: model-based testing, specification-based testing, formal methods, test automation, test generation.