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

it('should deselect the current cell if the cell above is selected', () => {
        NotebookActions.extendSelectionBelow(widget);
        NotebookActions.extendSelectionBelow(widget);
        const cell = widget.activeCell;
        NotebookActions.extendSelectionAbove(widget);
        expect(widget.isSelected(cell)).to.equal(false);
      });

it('should select only the first cell if we move from the second to first', () => {
        NotebookActions.extendSelectionBelow(widget);
        const cell = widget.activeCell;
        NotebookActions.extendSelectionAbove(widget);
        expect(widget.isSelected(cell)).to.equal(false);
        expect(widget.activeCellIndex).to.equal(0);
      });

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

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

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

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

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

    execute: () => NotebookActions.extendSelectionBelow(nbWidget.content, true)
  });

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

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

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

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