For a number of years now, we have investigated the possibility of applying the process-algebraic theory of testing pre-orders to the practical problems of actual testing, most notably to the problem of test generation. This has turned out to be a very interesting area of research, where the interaction between theory and practice has led not only to better algorithms and tools to derive test suites from specifications, but also motivated new theoretical developments. In our presentation we will give an overview of the research in this area, presenting its historical development, the main results and the open problems.