register: (completable: ICompletionManager.ICompletable): ICompletionManager.ICompletableAttributes => {
        const { editor, session, parent } = completable;
        const model = new CompleterModel();
        const completer = new CompleterWidget({ editor, model });
        const handler = new CompletionHandler({ completer, session });
        const id = parent.id;

        // Hide the widget when it first loads.
        completer.hide();

        // Associate the handler with the parent widget.
        handlers[id] = handler;

        // Set the handler's editor.
        handler.editor = editor;

        // Attach the completer widget.
        Widget.attach(completer, document.body);

        // Listen for parent disposal.
        parent.disposed.connect(() => {
          delete handlers[id];
          model.dispose();
          completer.dispose();
          handler.dispose();
        });

        return handler;
      }

 it('should not signal when options have not changed', () => {
   let model = new CompleterModel();
   let called = 0;
   let listener = (sender: any, args: void) => { called++; };
   model.stateChanged.connect(listener);
   expect(called).to.be(0);
   model.setOptions(['foo']);
   model.setOptions(['foo']);
   expect(called).to.be(1);
   model.setOptions(['foo'], {foo: 'instance'});
   model.setOptions(['foo'], {foo: 'instance'});
   expect(called).to.be(2);
   model.setOptions([], {});
   model.setOptions([], {});
   expect(called).to.be(3);
 });

 it('should return undefined if original request or cursor are null', () => {
   let model = new CompleterModel();
   expect(model.createPatch('foo')).to.be(undefined);
 });

 parent.disposed.connect(() => {
   delete handlers[id];
   model.dispose();
   completer.dispose();
   handler.dispose();
 });