Quality: The Process, Part II [Expanding our repertoire]

[continued from Development environment]

Expanding our repertoire

Most development environments include a debugger, which is an essential tool for producing quality software. However, the function of a debugger goes well beyond merely helping to find bugs. Some programmers do not regularly use a debugger, or only use one to help locate “that tough bug.” If you fall into this category, I strongly urge you to familiarize yourself with a debugger and integrate it into your standard development process.

Using a debugger for code assurance is another form of glass box testing. It is most powerful when used to perform live walkthroughs of program code. You can manually step through your code, examining variables, and make sure that it is performing as expected. There is no better way to assure yourself that the program is performing correctly than to actually watch it. It also helps identify situations where an errant value could cause problems.

To put this capability to work for you, set a breakpoint at the beginning of each new routine. When the breakpoint triggers, step through the code line by line, confirming that the variables are correct and that the process produces the desired results. Some authorities recommend setting a breakpoint at every single code path, only removing a breakpoint when the path has been thoroughly tested. I must admit that I find this to be overkill in some situations, such as where the function is simply returning an error code, but I do this for all significant branches.

Another glass box testing tool that is often provided with common development environments is a profiler. A profiler is a tool that takes time measurements of a running application and then provides performance statistics for modules or specific functions. This is useful for identifying performance bottlenecks and functional irregularities in a program.

There are two important metrics provided by most profilers, function time and execution count. The function time shows how much overall time was spent in a function (or module), which gives an indication of where any performance delays may be. The execution count shows how many times a function was called, and occasionally this highlights an unexpected problem if a routine is being called too often.

Together, the time and count metrics help show where a program can benefit from optimization, and it is useful to have this information. However, unless there is a serious problem, it is best to wait until all program functionality is complete before attempting to optimize. There is a term in the industry for unnecessarily modifying code for performance before having functionality: “premature optimization”.

There are more powerful profilers and debuggers available from third-party suppliers, but I recommend getting comfortable with the capabilities and features, as well as drawbacks, of the tools provided by your compiler vendor before evaluating expensive alternatives. The quality improvement to be gained by using any debugger far outweighs the incremental benefit of switching to a more powerful tool.

[continued in Beyond the build]

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