I use a roll-yer-own test framework that (I believe) strikes the perfect balance between setup costs, simplicity and flexibility. It's a small utility that just looks through a given directory tree, finds folders called */test, compiles and runs each .cpp file in that folder (taking cues from formatted comments inside the file if additional files are required), and compares the output to a stored 'good' output for that file, flagging an error if the files differ.

When developing code, you'll almost always end up writing some ad-hoc testing code anyway: Generate some input data, call the code you're testing, printf() some results. At development time, you read this output to verify your code's working well. My system just makes this a bit more methodical and saves a 'known good' result - if the output changes then the code may be wrong. Once you've fixed the issue (or determined that the new behaviour is in fact correct) you update the known-good output.

Dead simple, basically maintains itself, still catches any problems that the tests would catch.