Sets the assessment.

        arg:    assessmentId (osid.id.Id): the new assessment
        raise:  INVALID_ARGUMENT - assessmentId is invalid
        raise:  NoAccess - assessmentId cannot be modified
        raise:  NullArgument - assessmentId is null
        compliance: mandatory - This method must be implemented.

def set_assessment(self, assessment_id=None):
        """Sets the assessment.

        arg:    assessmentId (osid.id.Id): the new assessment
        raise:  INVALID_ARGUMENT - assessmentId is invalid
        raise:  NoAccess - assessmentId cannot be modified
        raise:  NullArgument - assessmentId is null
        compliance: mandatory - This method must be implemented.

        """
        if assessment_id is None:
            raise NullArgument()
        metadata = Metadata(**settings.METADATA['assessment_id'])
        if metadata.is_read_only():
            raise NoAccess()
        if self._is_valid_input(assessment_id, metadata, array=False):
            self._my_map['assessmentId'] = str(assessment_id)
        else:
            raise InvalidArgument