it('should paste when clicked', async () => {
   const button = ToolbarItems.createPasteButton(panel);
   const count = panel.content.widgets.length;
   Widget.attach(button, document.body);
   await framePromise();
   NotebookActions.copy(panel.content);
   (button.node.firstChild as HTMLElement).click();
   await sleep();
   expect(panel.content.widgets.length).to.equal(count + 1);
   button.dispose();
 });

 it('should emit a tick identical to the poll state', async () => {
   poll = new Poll<void, void>({
     factory: () => Promise.resolve(),
     frequency: { interval: 100, backoff: false },
     name: '@jupyterlab/test-coreutils:Poll#ticked-3'
   });
   poll.ticked.connect((_, tick) => {
     expect(tick).to.equal(poll.state);
   });
   await sleep(250);
 });

      it('should resolve after the reveal and context ready promises', async () => {
        const x = Object.create(null);
        const reveal = sleep(300, x);
        const contextReady = Promise.all([context.ready, x]);
        const widget = new DocumentWidget({ context, content, reveal });
        expect(widget.isRevealed).to.equal(false);

        // Our promise should resolve before the widget reveal promise.
        expect(await Promise.race([widget.revealed, reveal])).to.equal(x);
        // The context ready promise should also resolve first.
        context.initialize(true);
        expect(
          await Promise.race([widget.revealed, contextReady])
        ).to.deep.equal([undefined, x]);
        // The widget.revealed promise should finally resolve.
        expect(await widget.revealed).to.be.undefined;
      });