@abc.abstractmethod<EOL><INDENT>def get_assessments_taken(self):<DEDENT>
return<EOL>
Gets all ``AssessmentTaken`` elements.

        In plenary mode, the returned list contains all known
        assessments taken or an error results. Otherwise, the returned
        list may contain only those assessments taken that are
        accessible through this session.

        :return: a list of ``AssessmentTaken`` elements
        :rtype: ``osid.assessment.AssessmentTakenList``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure occurred

        *compliance: mandatory -- This method must be implemented.*