CxxTest is a unit testing framework for C++ that is similar in spirit to JUnit, CppUnit, and xUnit. CxxTest is easy to use because it does not require precompiling a CxxTest testing library, it employs no advanced features of C++ (e.g. RTTI) and it supports a very flexible form of test discovery.
I use CxxTest to develop unit tests for a complex software product. Very pleased with its ease of use, although the documentation could benefit from more examples of use, in my opinion.
Follow the links, and download the user manual or view it online. Great portable test suite. Extensible, yes: fully featured and hard to learn, No.