Running single tests with CppUnit?

As a C++ programmer you are probably used to, and have accepted, the verbose code you have to write in order to set up a test case with CppUnit. C++ does not have the flexibility like other languages that can know about test cases by naming conventions etc and then set up almost everything automatically. In C++ you need to do most of that yourself by coding it.

So once upon a time you set up the boiler plate code from the CppUnit Cookbook to get the framework for your unit tests installed. Your main test program could very well look like this.

#include <cppunit/extensions/TestFactoryRegistry.h>
#include <cppunit/ui/text/TestRunner.h>

int main(int argc, char **argv)
{
  CppUnit::TextUi::TestRunner runner;
  CppUnit::TestFactoryRegistry &registry = CppUnit::TestFactoryRegistry::getRegistry();
  runner.addTest(registry.makeTest());
  bool wasSuccessful = runner.run("", false);
  return wasSuccessful;
}

This is what it takes to run your test cases using the TextUi::TestRunner?. At that time you had a small set of tests but, as the project continued, more tests were added. And now after some time, if you did your homework right, your test suite is anything from small. In fact it is starting to take some time to execute. To long time. When you are developing new test cases it has become a bottle neck in the test, code and refactor loop.

So you would like to limit the number of test cases you run in order to get up to speed. Can it be done? Yes!

The solution lies in that old code you picked from the Cookbook so long ago you hardly remember it. Maybe you, like me, lived long enough with it to assume that it is so it must be in C++ being such a verbose and non dynamic language as it is. Maybe you, like me, have used comments or preprocessor constructs to hide tests. Was I wrong! Single tests can be run. It has been there all the time at my finger tips. If you look carefully at the Cookbook code you'll see that the first parameter of the run method is an empty string. That string parameter is actually the name of the test or the test suite to run! The empty string is only the special case of running all tests!

Now equipped with this knowledge it is easy to change the code to allow us to specify what test to run. The most straight forward is to use the first arg, if present, to the unit test program to be the test case to run. Like this:

  ...
  bool wasSuccessful = runner.run((argc > 1) ? argv[1] : "", false);
  ...