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.
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.
I've just pushed my own framework, CATCH, out there. It's still under development but I believe it already surpasses most other frameworks. Different people have different criteria but I've tried to cover most ground without too many trade-offs. Take a look at my linked blog entry for a taster. My top five features are:
It also has Objective-C bindings.
See also the answers to the closely related question "choosing a c++ unit testing tool/framework", here
There also is TUT, Template-Unit-Test, a template-based framework. It's syntax is awkward (some called it template-abusing), but its main advantage is that is it all contained in a single header file.
You'll find an example of unit-test written with TUT here.
I've tried CPPunit and it's not very user friendly.
The only alternative I know is using C++.NET to wrap your C++ classes and writing unit tests with one of .NET unit testing frameworks (NUnit, MBUnit etc.)
Michael Feathers of ObjectMentor was instrumental in the development of both CppUnit and CppUnitLite.
He now recommends CppUnitLite
Have a look at cfix (http://www.cfix-testing.org), it's specialized for Windows C/C++ development and supports both user mode and kernel mode unit testing.
If you are on Visual Studio 2008 SP1, I would highly recommend using MSTest for writing the unit tests. I then use Google mock for writing the mocks. The integration with the IDE is ideal and allows and doesn't carry the overhead of CPPunit in terms of editing three places for the addition of one test.
Check out fructose: http://sourceforge.net/projects/fructose/
It's a very simple framework, containing only header files and thus easy portable.
