[isityouyesitsme]

Whether or not it is enough depends on the context. Some cases require 100% condition and decision coverage. In these cases, it gets to be very difficult to achieve that unless you are directly testing the functions you write, not through a caller.

But even deeper, it is "accidental" because you are not testing contracts on the public APIs, you're testing the private functions through a layer higher. When the implementation changes, you have coupled your tests so tightly to the implementation that they are useless for regression testing. If not, then you actually aren't testing the private function at all, you're just hitting some parts by coincidence.