If you were super-disciplined, you would code unit tests before coding your objects. I’m not that disciplined.

I write the unit test alongside writing my objects. I write a few obvious member functions first, like the constructors and destructor, then write the unit tests that validate those functions. Then I write more unit tests as a way to suss out what the interface should look like, and then code those functions.

Sometimes my unit tests are hard to write because I need to bring in a boatload of other classes. That tells me my class is too strongly coupled. I pass in a pointer or reference to the other class, and all of a sudden I can also write mocks of these classes to provide extra clarity in the tests. Sometimes I find I need a new function at the interface to make the tests work. That’s OK. An interface function useful for testing might be useful in coding interactions with the class too.