Generating String Test Data for Code Coverage

String data has traditionally been difficult for test data generation tools to generate. Of particular concern are strings that conform to a given grammar, since coverage of grammar productions does not guarantee high code coverage or fault-finding ability. We address this problem by deriving Java classes from the grammatical categories in the grammar, and then using a collection of deterministic and met heuristic techniques to generate strings from them. We compare the code coverage of these techniques and the standard conformance test suites for the grammars. We conclude that the various techniques have complementary strengths, and that they can be usefully used in combination.