unit testing with rxPreference

[AshokSennanOkCredit]

while writing unit testing, I cannot return the rxPreference.getString() as Preference<String> since RealPreference() class is the only class which implements Preference<String> that too final class.

org.mockito.exceptions.misusing.WrongTypeOfReturnValue: String cannot be returned by getString() getString() should return Preference

how to return the Preference<String> in junit