For C++, there are lots of good unit test frameworks out there, but I couldn't find a good one for functional testing. With functional testing, I mean stuff which touches the disk, requires the whole application to be in place etc.
Point in case: What framework helps with testing things like whether your I/O works? I've got a hand-rolled system in place, which creates temporary folders, copies around a bunch of data, so the tests are always done in the same environment, but before I spend more time on my custom framework -- is there a good one out there already?
I wrote one from scratch three times already - twice for testing C++ apps that talked to exchanges using FIX protocol, once for a GUI app.
The problem is, you need to emulate the outside world to do proper system testing. I don't mean "outside of your code" - outside of your application. This involves emulating end users, outside entities, the Internet and so on.
I usually use perl to write my system testing framework and tests, mostly because it's good with accessing all sorts of OS facilities and regexps are first-class citizens.
Some tips: make sure your logs are easy to parse, detailed but not too verbose. Have a sane default configuration. Make it easy to "reset" the application - you need to do it after each test.
The approach I usually use is to have some sort of "adapter" that turns the application's communications with the outside world into stdin/stdout of some executable. Then I build a perl framework on top of that, and then the test cases use the framework.