This is sort of what I've done with some success in developing games. Games in general are grossly under-tested, but there are a few good reason for that. Lots of systems can be effectively tested by just playing, and often it's tough to tease out as small of units for useful isolated testing as you would in other types of programs.

What I've been doing is writing as many parts of the game as libraries as is possible, and then implementing the minimal possible usage of that library as a semi-automated test. For instance, our collision system is implemented as a library, and you can load up a "game" that has the simplest possible renderer, no sound, basic inputs, etc. and has a small world you can run around in that's filled with edge cases. This was vastly easier than trying to write automated tests for 3d collision code, and you get the benefit of testing the system in isolation, if not automatically. For other libraries like networking, the tests are much more automated, but they poke the library as a unit, rather than testing all the little bits and pieces individually.