In the example given, there are two possible scenarios.
1) The intention is to test how each version of a piece of code handles a specific problem. In this case, you're exactly right.
2) The intention is to test how each piece of code is performing in a larger prog. In this case, both the performance of the individual segments and the interactions among those segments in the real-world case are valuable, so you want both the 'isolated' and 'non-isolated' cases.
In any event, I like the module. In case 1, it allows for testing of several very similar segments of code non-interactively at once, regardless of whether the coder knows they would otherwise be interactive. (Another goot habit, like 'use strict'.)