TracePoint Visual Coverage 1.0

Dr. Dobb's Journal March 1998

Visual Coverage determines which parts and paths of your program have been reached during a particular run. After instrumenting your program and running it through one or more test cases similar to TracePoint's HiProf profiler, data is displayed on various coverage metrics. You can choose from function coverage (the percentage of functions reached by the test runs), line coverage (ditto, for source-code lines), code coverage (for CPU instructions), edge coverage (for branches), and call-pair coverage (for call sites). Visual Coverage uses almost the same views as HiProf 1.0 does for displaying data, so you'll find a function list, hierarchical view, source view, and, unique to Visual Coverage, a function distribution view that displays a bar chart with coverage percentages. Where appropriate, views can be switched to display the different forms of coverage data. Finally, since coverage information is usually collected over several test runs, both the combined and the separate data can be viewed.

Coverage tools are intended as an aid during testing. In particular, they help to find out which parts of a program have been exercised and which have not. To some extent, profilers can be used for the same purpose, but information like edge and call-pair coverage is difficult to obtain without special measurements. In addition, Visual Coverage sorts out all data for you and, as with the profilers, a clear presentation of the data greatly aids analysis. Visual Coverage does an admirable job here; apart from the views mentioned, several higher level selection options filter the data before they get to the views. To this end, the navigator window contains several predefined categories that isolate dead or unused functions, functions organized per class, or functions organized per module. If desired, further categories can be defined based on coverage type and cut-off percentages for filtering.

In daily use, I found that using a coverage tool requires more discipline than using a profiler. While a profiler provides instant gratification when you see the performance improvements, a coverage tool sits there as an administrator and points out that you still haven't tested all your code. To be of any real use, therefore, you need to be systematic in your approach to test cases and you must be prepared to spend considerable time studying the coverage information and building new test cases. For console applications, this is not normally a problem; for GUI applications, however, this means that you have to instrument the application first, then use Rational's Visual Test or a similar test harness to run the instrumented version of the application through different test scenarios. The resulting coverage data can then be viewed with the Visual Coverage GUI.

--R.v.d.W.