About testing private methods

I’ve loved the next sentence, read here:

The more tests the more attention they need. We can reduce the time we spend on nurturing by writing test only against public method. Public methods are contract. If we specify some contract we will rather not change it as often as private methods. If you feel that you have to test private method it is a sign of a bad design (it’s called “code smell”). Probably functionality of this method belongs elsewhere.