function toggleAllLineNumbers(widget: Notebook): void {
   if (!widget.model || !widget.activeCell) {
     return;
   }
   let lineNumbers = widget.activeCell.editor.lineNumbers;
   each(widget.widgets, child => {
     child.editor.lineNumbers = !lineNumbers;
   });
 }

 it('should insert a widget into the tab panel at a specified index', () => {
   let panel = new TabPanel();
   let widgets = [new Widget(), new Widget(), new Widget()];
   each(widgets, w => { panel.addWidget(w); });
   let widget = new Widget();
   panel.insertWidget(1, widget);
   expect(panel.widgets[1]).to.equal(widget);
   expect(panel.tabBar.titles[1]).to.equal(widget.title);
 });

 it('should add a class name to the flex panel children', () => {
   let p = new FlexPanel();
   p.addWidget(new Widget());
   p.addWidget(new Widget());
   p.addWidget(new Widget());
   each(p.widgets, (child) => {
     expect(child.hasClass('p-FlexPanel-child')).to.be(true);
   });
 });

 /**
  * Create the footer of the dialog.
  *
  * @param buttonNodes - The buttons nodes to add to the footer.
  *
  * @returns A widget for the footer.
  */
 createFooter(buttons: ReadonlyArray<HTMLElement>): Widget {
   let footer = new Widget();
   footer.addClass('jp-Dialog-footer');
   each(buttons, button => {
     footer.node.appendChild(button);
   });
   Styling.styleNode(footer.node);
   return footer;
 }

 function runAll(widget: Notebook, kernel?: Kernel.IKernel): Promise<boolean> {
   if (!widget.model || !widget.activeCell) {
     return Promise.resolve(false);
   }
   each(widget.widgets, child => {
     widget.select(child);
   });
   return run(widget, kernel);
 }

 function clearAllOutputs(widget: Notebook): void {
   if (!widget.model || !widget.activeCell) {
     return;
   }
   each(widget.model.cells, (cell: ICodeCellModel) => {
     if (cell.type === 'code') {
       cell.outputs.clear();
       cell.executionCount = null;
     }
   });
 }

 function toggleAllLineNumbers(widget: Notebook): void {
   if (!widget.model || !widget.activeCell) {
     return;
   }
   let state = Private.getState(widget);
   let lineNumbers = widget.activeCell.editor.lineNumbers;
   each(widget.widgets, child => {
     child.editor.lineNumbers = !lineNumbers;
   });
   Private.handleState(widget, state);
 }

 it('should break early if the callback returns `false`', () => {
   let result = 0;
   let data = [1, 2, 3, 4, 5];
   each(data, x => {
     if (x > 3) {
       return false;
     }
     result += x;
     return true;
   });
   expect(result).to.equal(6);
 });

 execute: () => {
   const promises: Promise<void>[] = [];
   const paths = new Set<string>(); // Cache so we don't double save files.
   each(shell.widgets('main'), widget => {
     const context = docManager.contextForWidget(widget);
     if (context && !context.model.readOnly && !paths.has(context.path)) {
       paths.add(context.path);
       promises.push(context.save());
     }
   });
   return Promise.all(promises);
 }