If you end up mocking every non-private method of a class in order to write tests, it is a strong sign that your test became too complex, or that you misunderstood the way you are supposed to use the mocking mechanism.
You should either refactor the test code into multiple units, or consider using the class itself, by either directly instantiating it, or creating a new one inheriting from it, with the expected behavior.
This rule reports an issue when every member of a given class are mocked.