Unit testing for C++ code - Tools and methodology [closed]

I'm working on a large c++ system that is has been in development for a few years now. As part of an effort to improve the quality of the existing code we engaged on a large long-term refactoring project.

Do you know a good tool that can help me write unit tests in C++? Maybe something similar to Junit or Nunit?

Can anyone give some good advice on the methodology of writing unit tests for modules that were written without unit testing in mind?

Applying unit tests to legacy code was the very reason Working Effectively with Legacy Code was written. Michael Feathers is the author - as mentioned in other answers, he was involved in the creation of both CppUnit and CppUnitLite.

Google recently released their own library for unit testing C++ apps, called Google Test.

Project on Google Code

Check out an excellent comparison between several available suites. The author of that article later developed UnitTest++.

What I particularly like about it (apart from the fact that it handles exceptions etc. well) is that there is a very limited amount of 'administration' around the test cases and test fixtures definition.

Boost has a Testing library which contains support for unit testing. It might be worth checking out.

Noel Llopis of Games From Within is the author of Exploring the C++ Unit Testing Framework Jungle, a comprehensive (but now dated) evaluation of the various C++ Unit Testing frameworks, as well as a book on game programming.

He used CppUnitLite for quite a while, fixing various things, but eventually joined forces with another unit test library author, and produced UnitTest++. We use UnitTest++ here, and I like it a lot, so far. It has (to me) the exact right balance of power with a small footprint.

I've used homegrown solutions, CxxTest (which requires Perl), and boost::test. When I implemented unit testing here at my current job it pretty much came down to UnitTest++ vs boost::test.

I really like most boost libraries I have used, but IMHO, boost::test is a little too heavy-handed. I especially did not like that it requires you (AFAIK) to implement the main program of the test harness using a boost::test macro. I know that it is not "pure" TDD, but sometimes we need a way to run tests from withing a GUI application, for example when a special test flag is passed in on the command line, and boost::test cannot support this type of scenario.

UnitTest++ was the simplest test framework to set up and use that I have encountered in my (limited) experience.