Functional testing of a query language is a challenging task in practice. In order to reveal errors in the query processing functionality, it is necessary to verify the actual result of a test query with the expected correct result. However, automatically computing the expected query result of an arbitrary test query is not trivial. One solution is to first generate a set of test database instances as well as test queries and then to compute the expected result for each test query over the individual test database instances just like in forward query processing. The problem of this solution is, that many test queries might return an empty query result which is not interesting for the functional testing of a query language. In this paper, we present a new approach which provides a different solution to the verification of the actual result of a test query. Instead of first generating the database instance and then computing the expected result for each test query, we first create one o...