How to use the @jupyterlab/notebook.NotebookActions.mergeCells function in @jupyterlab/notebook

it('should preserve the widget mode', () => {
        widget.mode = 'edit';
        NotebookActions.mergeCells(widget);
        expect(widget.mode).to.equal('edit');
        widget.mode = 'command';
        NotebookActions.mergeCells(widget);
        expect(widget.mode).to.equal('command');
      });

it('should be a no-op if there is no model', () => {
        widget.model = null;
        NotebookActions.mergeCells(widget);
        expect(widget.activeCell).to.be.undefined;
      });

    execute: () => NotebookActions.mergeCells(nbWidget.content)
  });

    execute: () => NotebookActions.mergeCells(nbWidget.content)
  });

execute: args => {
      const current = getCurrent(args);

      if (current) {
        return NotebookActions.mergeCells(current.notebook);
      }
    },
    isEnabled

execute: args => {
      const current = getCurrent(args);

      if (current) {
        return NotebookActions.mergeCells(current.notebook);
      }
    },
    isEnabled

execute: args => {
                const current = getCurrent(args);

                if (current) {
                    const { content } = current;
                    NotebookActions.mergeCells(content);
                    current.content.mode = 'edit';
                }
            },
            isEnabled

    execute: () => NotebookActions.mergeCells(nbWidget.content)
  });

execute: args => {
      const current = getCurrent(args);

      if (current) {
        return NotebookActions.mergeCells(current.content);
      }
    },
    isEnabled

    execute: () => NotebookActions.mergeCells(nbWidget.notebook)
  });