The TSNLP project has investigated various aspects of the construction, maintenance and application of systematic test suites as diagnostic and evaluation tools for NLP applications. The paper summarizes the motivation and main results of the project: besides the solid methodological foundation, TSNLP has produced substantial multi-purpose and multi-user test suites for three European languages together with a set of specialized tools that facilitate the construction, extension, maintenance, retrieval, and customization of the test data. As TSNLP results, including the data and technology, are made publicly available, the project presents a valuable linguistic resourc e that has the potential of providing a wide-spread pre-standard diagnostic and evaluation tool for both developers and users of NLP applications.