private void modifyDiff(MPatchModel mpatch) {
    assertEquals("Number of changes doesn't match!", 3, mpatch.getChanges().size());

    // get model descriptor of add class 'B' change
    final EMFModelDescriptor subModel = getAddChangeModelDescriptor(mpatch.getChanges(), "B");
    final EList<Object> attribute =
        subModel.getAttributes().get(EcorePackage.Literals.ENAMED_ELEMENT__NAME);
    final Object name = attribute.get(0);
    assertEquals("Attribute name differs!", "B", name);

    // change to 'C' and verify
    attribute.set(0, "C");
    final Object newName =
        subModel.getAttributes().get(EcorePackage.Literals.ENAMED_ELEMENT__NAME).get(0);
    assertEquals("Attribute name should have changed to 'C'!", "C", newName);

    // get model descriptor of add class 'A2' change
    final IndepChange addChange =
        (IndepChange) getAddChangeModelDescriptor(mpatch.getChanges(), "A2").eContainer();
    final ElementSetReference corrReference =
        (ElementSetReference) addChange.getCorrespondingElement();
    final OclCondition condition = (OclCondition) corrReference.getConditions().get(0);
    condition.setExpression("name = 'root'"); // no weakening here!
  }
  /**
   * Create a symbolic reference which contains an ocl condition which holds the criteria for the
   * referenced model element given in the parameter.
   *
   * @param self The element which should be referenced.
   * @param contextDepth The depth for which context references should be created. If <code>0</code>
   *     , then no context reference is created.
   * @return A symbolic reference to the model element.
   */
  public ElementSetReference create(EObject self, int contextDepth) {
    final ElementSetReference ref = SymrefsFactory.eINSTANCE.createElementSetReference();
    ref.setType(self.eClass());
    ref.setUriReference(QvtlibHelper.getUriString(self));
    ref.setLabel(QvtlibHelper.getLabel(self));
    ref.getConditions().add(createOclCondition(self));

    // the context can of course only be set if the parent exists
    if (contextDepth > 0 && self.eContainer() != null) {
      ref.setContext(create(self.eContainer(), contextDepth - 1));
    }

    return ref;
  }