Kapil Saxena

Software testing is more and more considered a problematic method toward better quality. Using testing to locate and correct software defects can be an endless process. Bugs cannot be completely ruled out. Just as the complexity barrier indicates: chances are testing and fixing problems may not necessarily improve the quality and reliability of the software. Sometimes fixing a problem may introduce much more severe problems into the system, happened after bug fixes, such as the telephone outage in California and eastern seaboard in 1991. The disaster happened after changing 3 lines of code in the signaling system.

In a narrower view, many testing techniques may have flaws. Coverage testing, for example. Is code coverage, branch coverage in testing really related to software quality? There is no definite proof. As early as in 79, the so-called "human testing” -- including inspections, walkthroughs, reviews -- are suggested as possible alternatives to traditional testing methods. Inspection is a cost-effect alternative to unit testing. The experimental results suggests that code reading by stepwise abstraction is at least as effective as on-line functional and structural testing in terms of number and cost of faults observed.

Using formal methods to "prove" the correctness of software is also an attracting research direction. But this method cannot surmount the complexity barrier either. For relatively simple software, this method works well. It does not scale well to those complex, full-fledged large software systems, which are more error-prone.

In a broader view, we may start to question the utmost purpose of testing. Why do we need more effective testing methods anyway, since finding defects and removing those does not necessarily lead to better quality? An analogy of the problem is like the car manufacturing process. In the craftsmanship epoch, we make cars and hack away the problems and defects. But such methods were washed away by the tide of pipelined manufacturing and good quality engineering process, which makes the car defect-free in the manufacturing phase. This indicates that engineering the design process (such as clean-room software engineering) to make the product have fewer defects may be more effective than engineering the testing process. Testing is used solely for quality monitoring and management, or, "design for testability". This is the leap for software from craftsmanship to engineering.