Hybrid Is Better: Why and How Test Coverage and Software Reliability Can Benefit Each Other

Functional, structural and operational testing are three broad categories of software testing methods driven by the product functionalities, the way it is implemented, and the way it is expected to be used, respectively. A large body of the software testing literature is devoted to evaluate and compare test techniques in these categories. Although it appears reasonable to devise hybrid methods to merge their different strengths - because different techniques may complement each other by targeting different types of faults and/or using different artifacts - we still miss clear guidelines on how to best combine them. We discuss differences and limitations of two popular testing approaches, namely coverage-driven and operational-profile testing, belonging to structural and operational testing, respectively. We show why and how test coverage and operational profile can cross-fertilize each other, improving the effectiveness of structural testing or, conversely, the product reliability achievable by operational testing.