Measuring design testability of a UML class diagram

Design-for-testability is a very important issue in software engineering. It becomes crucial in the case of OO designs where control flows are generally not hierarchical, but are diffuse and distributed over the whole architecture. In this paper, we concentrate on detecting, pinpointing and suppressing potential testability weaknesses of a UML class diagram. The attribute significant from design testability is called 'class interaction' and is generalized in the notion of testability anti-pattern: it appears when potentially concurrent client/supplier relationships between classes exist in the system. These interactions point out parts of the design that need to be improved, driving structural modifications or constraints specifications, to reduce the final testing effort. In this paper, the testability measurement we propose counts the number and the complexity of interactions that must be covered during testing. The approach is illustrated on application examples.