We end this book with a discussion of three challenging areas in testing software. Although researchers have been interested in emergent properties for many years, the area, far from being “solved,” continues to escalate in terms of importance for industry. Likewise, testability is attracting renewed attention due to characteristics of some of the newer software technologies. Finally, we suggest some directions for software testing in practice and in the research arena.

TESTING FOR EMERGENT PROPERTIES: SAFETY AND SECURITY

Testing for emergent properties presents special challenges. This section offers high level guidance for engineers faced with testing systems where safety and/or security play an important role.

Emergent properties arise as a result of collecting components together into a single system. They do not exist independently in any particular component. Safety and security are classic emergent properties in system design. For example, the overall safety of an airplane is not determined by the control software by itself, or the engines by themselves, or by any other component by itself. Certainly, the individual behavior of a given component may be extremely important with respect to overall safety, but, even so, the overall safety is determined by the interactions of all of these components when assembled into a complete airplane. In other words, an airplane engine is neither safe nor unsafe considered by itself because an airplane engine doesn't fly by itself.