Test Generation with Context Free Grammars and Covering Arrays

Covering arrays and context-free grammars have seen extensive use in software test generation. A covering-array algorithm takes a list of domains and generates a subset of the cartesian product of the domains. A grammar-based test generation (GBTG) algorithm takes a grammar G and generates a subset of the language accepted by G. Covering arrays and GBTG are usually applied independently. We show that CFG rules and covering-array specifications can be freely intermixed, with precise, intuitive semantics and efficient generation. We present a novel approach for ``tagging'' grammars with specifications for mixed-strength covering arrays, a generalization of conventional covering arrays. We have developed algorithms for test generation and implemented a tool for generating test cases from tagged grammars.