Nowadays, business processes and their execution are corner stones in modern IT landscapes, as multiple process languages and corresponding engines for these languages have emerged. In practice, it is not feasible to select the best fitting engine, as engine capabilities are mostly hidden in the engine implementation and a comparison is hampered by the large differences and high adoption costs of the engines. We aim to overcome these problems by a) introducing an abstract layer to access the functionality of the engines uniformly, b) by revealing the engine capabilities through automated and isolated tests for typical requirements, and c) support the user in their selection of a process engine by determining and explaining the fitness of the engines for a single process or a given set of processes using policy matching against previously revealed engine capabilities. Early results show the general feasibility of our approach for BPEL engines for a single capability.