Generating Test Data to Distinguish Conjunctive Queries with Equalities

The widespread use of databases in software systems has increased the importance of unit testing the queries that form the interface to these databases. Mutation analysis is a powerful testing technique that has been adapted to test database queries. But each of the existing mutation approaches to testing database queries has one or more of the following shortcomings: inability to recognize equivalent mutants, inability to generate test databases automatically, or inability to mutate all aspects of a query. In this paper we address all three of these challenges by adapting results from the rich literature on query rewriting. We restrict attention to the class of conjunctive queries with equalities. In return for this restriction, we give an algorithm that recognizes equivalent mutants, generates a test database that distinguishes each nonequivalent mutant, and applies to arbitrary mutations, as long at the mutation is also a conjunctive query with equalities. The paper presents the test database generation algorithm and proves that it is sound and complete for conjunctive queries with equalities. We then illustrate the algorithm on a sample query. We evaluate mutations of the query both with the new technique and compare the results to existing mutation techniques for databases.