How to use the @jupyterlab/completer.Completer function in @jupyterlab/completer

it('should call model change handler if model exists', () => {
        const completer = new Completer({
          editor: null,
          model: new TestCompleterModel()
        });
        const handler = new TestCompletionHandler({ completer, connector });
        const editor = createEditorWidget().editor;
        const model = completer.model as TestCompleterModel;

        handler.editor = editor;
        expect(model.methods).to.not.contain('handleTextChange');
        editor.model.value.text = 'bar';
        editor.setCursorPosition({ line: 0, column: 2 });
        // This signal is emitted (again) because the cursor position that
        // a natural user would create need to be recreated here.
        (editor.model.value.changed as any).emit({ type: 'set', value: 'bar' });
        expect(model.methods).to.contain('handleTextChange');
      });

editor.setCursorPosition(position);

          let request: Completer.ITextState = {
            column: position.column,
            lineHeight: editor.lineHeight,
            charWidth: editor.charWidth,
            line: position.line,
            text: 'a'
          };

          model.original = request;
          model.cursor = { start: text.length - 1, end: text.length };
          model.setOptions(['abc', 'abd', 'abe', 'abi']);

          let widget = new Completer({ model, editor: code.editor });
          Widget.attach(widget, document.body);
          MessageLoop.sendMessage(widget, Widget.Msg.UpdateRequest);
          simulate(document.body, 'scroll');

          // Because the scroll handling is asynchronous, this test uses a large
          // timeout (500ms) to guarantee the scroll handling has finished.
          await sleep(500);
          let top = parseInt(window.getComputedStyle(widget.node).top, 10);
          let bottom = Math.floor(coords.bottom);
          expect(top + panel.node.scrollTop).to.equal(bottom);
          widget.dispose();
          code.dispose();
          panel.dispose();
        });
      });

canStartKernel: true,
    rendermime,
    contentFactory,
    mimeTypeService: editorServices.mimeTypeService
  });
  docRegistry.addModelFactory(mFactory);
  docRegistry.addWidgetFactory(wFactory);

  let notebookPath = PageConfig.getOption('notebookPath');
  let nbWidget = docManager.open(notebookPath) as NotebookPanel;
  let palette = new CommandPalette({ commands });

  const editor =
    nbWidget.content.activeCell && nbWidget.content.activeCell.editor;
  const model = new CompleterModel();
  const completer = new Completer({ editor, model });
  const connector = new KernelConnector({ session: nbWidget.session });
  const handler = new CompletionHandler({ completer, connector });

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

  // Listen for active cell changes.
  nbWidget.content.activeCellChanged.connect((sender, cell) => {
    handler.editor = cell && cell.editor;
  });

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

  let panel = new SplitPanel();
  panel.id = 'main';

fileExtensions: ['.ipynb'],
    defaultFor: ['.ipynb'],
    preferKernel: true,
    canStartKernel: true,
    rendermime, contentFactory,
    mimeTypeService: editorServices.mimeTypeService
  });
  docRegistry.addModelFactory(mFactory);
  docRegistry.addWidgetFactory(wFactory);

  let nbWidget = docManager.open(NOTEBOOK) as NotebookPanel;
  let palette = new CommandPalette({ commands });

  const editor = nbWidget.notebook.activeCell && nbWidget.notebook.activeCell.editor;
  const model = new CompleterModel();
  const completer = new Completer({ editor, model });
  const handler = new CompletionHandler({ completer, session: nbWidget.session });

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

  // Listen for active cell changes.
  nbWidget.notebook.activeCellChanged.connect((sender, cell) => {
    handler.editor = cell && cell.editor;
  });

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

  let panel = new SplitPanel();
  panel.id = 'main';
  panel.orientation = 'horizontal';

it('should be settable', () => {
        let widget = new Completer({ editor: null });
        expect(widget.model).to.be.null;
        widget.model = new CompleterModel();
        expect(widget.model).to.be.an.instanceof(CompleterModel);
      });

it('should create a completer widget', () => {
        let widget = new Completer({ editor: null });
        expect(widget).to.be.an.instanceof(Completer);
        expect(Array.from(widget.node.classList)).to.contain('jp-Completer');
      });

it('should accept options with a model', () => {
        let options: Completer.IOptions = {
          editor: null,
          model: new CompleterModel()
        };
        let widget = new Completer(options);
        expect(widget).to.be.an.instanceof(Completer);
        expect(widget.model).to.equal(options.model);
      });

it('should create a completer widget', () => {
        let widget = new Completer({ editor: null });
        expect(widget).to.be.an.instanceof(Completer);
        expect(Array.from(widget.node.classList)).to.contain('jp-Completer');
      });

editor.setCursorPosition(position);

        let request: Completer.ITextState = {
          column: position.column,
          lineHeight: editor.lineHeight,
          charWidth: editor.charWidth,
          line: position.line,
          text: 'a'
        };

        model.original = request;
        model.cursor = { start: 0, end: 1 };
        model.setOptions(['abc', 'abd', 'abe', 'abi']);

        let widget = new Completer({ model, editor: code.editor });
        widget.hide();
        expect(called).to.equal(false);
        widget.visibilityChanged.connect(() => {
          called = true;
        });
        Widget.attach(widget, document.body);
        MessageLoop.sendMessage(widget, Widget.Msg.UpdateRequest);

        await framePromise();
        expect(called).to.equal(true);
        widget.dispose();
        code.dispose();
        panel.dispose();
      });
    });

editor.setCursorPosition(position);

        let request: Completer.ITextState = {
          column: position.column,
          lineHeight: editor.lineHeight,
          charWidth: editor.charWidth,
          line: position.line,
          text: 'a'
        };

        model.original = request;
        model.cursor = { start: 0, end: 1 };
        model.setOptions(['abc', 'abd', 'abe', 'abi']);

        let widget = new Completer({ model, editor: code.editor });
        widget.hide();
        expect(called).to.equal(false);
        widget.visibilityChanged.connect(() => {
          called = true;
        });
        Widget.attach(widget, document.body);
        MessageLoop.sendMessage(widget, Widget.Msg.UpdateRequest);

        await framePromise();
        expect(called).to.equal(true);
        widget.dispose();
        code.dispose();
        panel.dispose();
      });
    });