public OpenConfigLogicalChannelAssignmentsHandler addAssignment(
                                                      OpenConfigAssignmentHandler assignment) {
        modelObject.addToAssignment(assignment.getModelObject());
        return this;
    }
@Test
    public void testAddAssignment() {
        // test Handler
        OpenConfigLogicalChannelAssignmentsHandler logicalChannelAssignments =
            new OpenConfigLogicalChannelAssignmentsHandler(parent);

        // call addAssignment
        OpenConfigAssignmentHandler assignment = new OpenConfigAssignmentHandler(2, logicalChannelAssignments);

        // expected ModelObject
        DefaultLogicalChannelAssignments modelObject = new DefaultLogicalChannelAssignments();
        DefaultAssignment assign = new DefaultAssignment();
        assign.index(2);
        modelObject.addToAssignment(assign);

        assertEquals("[NG]addAssignment:ModelObject(Assignment added) is not an expected one.\n",
                     modelObject, logicalChannelAssignments.getModelObject());
    }