In the observations of professional programmers that I did for my thesis, I frequently saw them get sidetracked because they didn’t have good information about whether the code they were looking at was executed as part of the feature they were exploring. I theorized that being able to look at the differences in code coverage between two runs — one where they exercised the feature and one where they didn’t — would be useful. Being able to see which methods executed in the first but not the second would hopefully help developers focus in quickly on the methods that were important to their task.
In my last month at UBC, I whipped up a prototype, an Eclipse plug-in called Tripoli, and ran a quickie user study. The differential code coverage information really does make a big difference. You can read a detailed account in UBC Technical Report TR-2008-14, but basically graduate students using Tripoli were frequently more successful than professional programmers who didn’t use Tripoli.
As an example, in the Size task, the subject needed to find where a pane was resized. That was hard. There is no menu item or key stroke invocation for developers to use a starting point. They also didn’t know what the pane was called: was it a canvas, a pane, a panel, a frame, a drawing, or a view? Between pilot subjects and actual subjects, at least eleven people tried and failed to find a method that was always called when a pane was resized and never called when it wasn’t. I even spent a few hours trying to figure out where the pane was resized and couldn’t.
As soon as I got Tripoli working, I tried the Size task, and in my first diff, I saw ten methods, including one named endResizingFrame(). And yes, it turned out to be the right spot. I realized that most of the methods came from not hovering over the corner of the frame such that the cursor changed into the grab handle, and reran. This time I got exactly one method: endResizingFrame(). Wow. The graduate students in my second study were also all able to find endResizingFrame() by using Tripoli.
Tripoli does take some getting used to. Even as the author, it took me a while before I consistently remembered right away that I could use Tripoli on my problems. I’ve also clearly gotten better over time at figuring out what to do in my second run to ensure that the “diff” has very few methods in it.
If you want to try Tripoli out, I’ve posted it online. Just remember it’s a prototype.