Unfortunately unmanaged C++ does not natively support Unit-tests. If you put some effort into your project structure and class definitions you can use testing frameworks such as boost::test (see link in solution 1), cppunit, or cppunitlite (links to the relevant pages should be easy to find)
I've looked at
winunit[
^] as well, and liked it best.:I think it's easy to use, and makes a better separation between functionality and testing frontend than any of the others. While the frontend is available as a binary, you can change the source code to adapt it to your own preferences.
If you're willing to shell out some cash (the above tools are all free), there are lots of testing tools to be had, but most of them only support NUnit-like interfaces. You'll still have to put some work into your code to make them usable by those testing tools.