human
Complete the below
@pytest.fixture()
def interface():

    ''''Returns the interface class for the composite.'
    '''

=====
What is a the Python program you requested?
assistant
#Here is the Python program you requested.
    class Base:
        counter = 0
        def add(self):
            raise NotImplemented('add    not    implemented')
        def subtract(self):
            raise NotImplemented('subtract    not    implemented')
    return Base