Software Architecture in Practice, Third Edition

10. Testability

Testing leads to failure, and failure leads to understanding

—Burt Rutan

Industry estimates indicate that between 30 and 50 percent (or in some cases, even more) of the cost of developing well-engineered systems is taken up by testing. If the software architect can reduce this cost, the payoff is large.

Software testability refers to the ease with which software can be made to demonstrate its faults through (typically execution-based) testing. Specifically, testability refers to the probability, assuming that the software has at least one fault, that it will fail on its next test execution. Intuitively, a system is testable if it “gives up” its faults easily. If a fault is present in a system, then we want it to fail during ...