How to use the @jupyterlab/docmanager.DocumentManager function in @jupyterlab/docmanager

it('should be resilient to a slow initial fetch', async () => {
        let delayedServiceManager = new ServiceManager();
        (delayedServiceManager as any).contents = new DelayedContentsManager();
        let manager = new DocumentManager({
          registry,
          opener,
          manager: delayedServiceManager
        });
        model = new FileBrowserModel({ manager, state });

        const paths: string[] = [];
        // An initial refresh is called in the constructor.
        // If it is too slow, it can come in after the directory change,
        // causing a directory set by, e.g., the tree handler to be wrong.
        // This checks to make sure we are handling that case correctly.
        const refresh = model.refresh().then(() => paths.push(model.path));
        const cd = model.cd('src').then(() => paths.push(model.path));
        await Promise.all([refresh, cd]);
        expect(model.path).to.equal('src');
        expect(paths).to.eql(['', 'src']);

if (!widget.isAttached) {
          shell.add(widget, 'main', options || {});
        }
        shell.activateById(widget.id);

        // Handle dirty state for open documents.
        let context = docManager.contextForWidget(widget);
        if (!contexts.has(context)) {
          handleContext(status, context);
          contexts.add(context);
        }
      }
    };
    const registry = app.docRegistry;
    const when = app.restored.then(() => void 0);
    const docManager = new DocumentManager({
      registry,
      manager,
      opener,
      when,
      setBusy: status.setBusy.bind(app)
    });

    // Register the file operations commands.
    addCommands(
      app,
      docManager,
      opener,
      settingRegistry,
      labShell,
      palette,
      mainMenu

document.addEventListener('keydown', event => {
    commands.processKeydownEvent(event);
  }, useCapture);

  let rendermime = new RenderMime({
    initialFactories: defaultRendererFactories
  });

  let opener = {
    open: (widget: Widget) => {
      // Do nothing for sibling widgets for now.
    }
  };

  let docRegistry = new DocumentRegistry();
  let docManager = new DocumentManager({
    registry: docRegistry,
    manager,
    opener
  });
  let mFactory = new NotebookModelFactory({});
  let editorFactory = editorServices.factoryService.newInlineEditor.bind(
    editorServices.factoryService);
  let contentFactory = new NotebookPanel.ContentFactory({ editorFactory });

  let wFactory = new NotebookWidgetFactory({
    name: 'Notebook',
    modelName: 'notebook',
    fileExtensions: ['.ipynb'],
    defaultFor: ['.ipynb'],
    preferKernel: true,
    canStartKernel: true,

let rendermime = new RenderMimeRegistry({
    initialFactories: initialFactories,
    latexTypesetter: new MathJaxTypesetter({
      url: PageConfig.getOption('mathjaxUrl'),
      config: PageConfig.getOption('mathjaxConfig')
    })
  });

  let opener = {
    open: (widget: Widget) => {
      // Do nothing for sibling widgets for now.
    }
  };

  let docRegistry = new DocumentRegistry();
  let docManager = new DocumentManager({
    registry: docRegistry,
    manager,
    opener
  });
  let mFactory = new NotebookModelFactory({});
  let editorFactory = editorServices.factoryService.newInlineEditor;
  let contentFactory = new NotebookPanel.ContentFactory({ editorFactory });

  let wFactory = new NotebookWidgetFactory({
    name: 'Notebook',
    modelName: 'notebook',
    fileTypes: ['notebook'],
    defaultFor: ['notebook'],
    preferKernel: true,
    canStartKernel: true,
    rendermime,

if (!widget.isAttached) {
          shell.add(widget, 'main', options || {});
        }
        shell.activateById(widget.id);

        // Handle dirty state for open documents.
        let context = docManager.contextForWidget(widget);
        if (!contexts.has(context)) {
          handleContext(status, context);
          contexts.add(context);
        }
      }
    };
    const registry = app.docRegistry;
    const when = app.restored.then(() => void 0);
    const docManager = new DocumentManager({
      registry,
      manager,
      opener,
      when,
      setBusy: status && (() => status.setBusy())
    });

    // Register the file operations commands.
    addCommands(
      app,
      docManager,
      opener,
      settingRegistry,
      labShell,
      palette,
      mainMenu

let rendermime = new RenderMimeRegistry({
    initialFactories: initialFactories,
    latexTypesetter: new MathJaxTypesetter({
      url: PageConfig.getOption('mathjaxUrl'),
      config: PageConfig.getOption('mathjaxConfig')
    })
  });

  let opener = {
    open: (widget: Widget) => {
      // Do nothing for sibling widgets for now.
    }
  };

  let docRegistry = new DocumentRegistry();
  let docManager = new DocumentManager({
    registry: docRegistry,
    manager,
    opener
  });
  let mFactory = new NotebookModelFactory({});
  let editorFactory = editorServices.factoryService.newInlineEditor;
  let contentFactory = new NotebookPanel.ContentFactory({ editorFactory });

  let wFactory = new NotebookWidgetFactory({
    name: 'Notebook',
    modelName: 'notebook',
    fileTypes: ['notebook'],
    defaultFor: ['notebook'],
    preferKernel: true,
    canStartKernel: true,
    rendermime,

document.addEventListener(
      'keydown',
      event => {
        this.commands.processKeydownEvent(event);
      },
      useCapture
    );

    let opener = {
      open: (widget: Widget) => {
        // Do nothing for sibling widgets for now.
      }
    };

    let docRegistry = new DocumentRegistry();
    let docManager = new DocumentManager({
      registry: docRegistry,
      manager: this.props.serviceManager,
      opener
    });
    let mFactory = new NotebookModelFactory({});
    let editorFactory = editorServices.factoryService.newInlineEditor;
    let contentFactory = new NotebookPanel.ContentFactory({ editorFactory });

    let wFactory = new NotebookWidgetFactory({
      name: 'Notebook',
      modelName: 'notebook',
      fileTypes: ['notebook'],
      defaultFor: ['notebook'],
      preferKernel: true,
      canStartKernel: true,
      rendermime: this.props.rendermime,

constructor(props: FileBrowserPageProps) {
    super(props);

    this.state = {
      currentPath: this.props.startingPath
    };

    let opener = {
      open: (widget: Widget) => {
        console.log(widget);
      }
    }
    let docRegistry = new DocumentRegistry();
    this.docManager = new DocumentManager({
      registry: docRegistry,
      manager: this.props.serviceManager,
      opener
    });

    let fbModel = new FileBrowserModel({
      manager: this.docManager,
    });
    fbModel.cd(this.state.currentPath);
    this.fileBrowser = new FileBrowser({
      id: 'filebrowser',
      model: fbModel
    });

    fbModel.pathChanged.connect(this.pathChanged);
  }

open: (widget: Widget) => {
      if (widgets.indexOf(widget) === -1) {
        dock.addWidget(widget, { mode: 'tab-after' });
        widgets.push(widget);
      }
      dock.activateWidget(widget);
      activeWidget = widget;
      widget.disposed.connect((w: Widget) => {
        let index = widgets.indexOf(w);
        widgets.splice(index, 1);
      });
    }
  };

  let docRegistry = new DocumentRegistry();
  let docManager = new DocumentManager({
    registry: docRegistry,
    manager,
    opener
  });
  let editorServices = {
    factoryService: new CodeMirrorEditorFactory(),
    mimeTypeService: new CodeMirrorMimeTypeService()
  };
  let wFactory = new FileEditorFactory({
    editorServices,
    factoryOptions: {
      name: 'Editor',
      modelName: 'text',
      fileTypes: ['*'],
      defaultFor: ['*'],
      preferKernel: false,

open: (widget: Widget) => {
      if (widgets.indexOf(widget) === -1) {
        dock.addWidget(widget, { mode: 'tab-after' });
        widgets.push(widget);
      }
      dock.activateWidget(widget);
      activeWidget = widget;
      widget.disposed.connect((w: Widget) => {
        let index = widgets.indexOf(w);
        widgets.splice(index, 1);
      });
    }
  };

  let docRegistry = new DocumentRegistry();
  let docManager = new DocumentManager({
    registry: docRegistry,
    manager,
    opener
  });
  let editorServices = {
    factoryService: new CodeMirrorEditorFactory(),
    mimeTypeService: new CodeMirrorMimeTypeService()
  };
  let wFactory = new FileEditorFactory({
    editorServices,
    factoryOptions: {
      name: 'Editor',
      modelName: 'text',
      fileTypes: ['*'],
      defaultFor: ['*'],
      preferKernel: false,