Is it ok to unit-test an abstract class by instantiating it as a mock object?

It has come to my attention that you can unit-test an abstract class by instantiating it as a mock object. Thereby you mock the abstract properties and methods, while being able to test the implemented ones.

However, I am accustomed to distinguish between the class to test and the injected dependencies to mock/stub. So, in this early stage of my new enlightenment I wonder if there are any pitfalls to this way of testing?? Any thoughts on this?

Regards, Мортен