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

it('should be clamped between 1 and 6', () => {
        NotebookActions.setMarkdownHeader(widget, -1);
        expect(widget.activeCell.model.value.text.slice(0, 2)).to.equal('# ');
        NotebookActions.setMarkdownHeader(widget, 10);
        expect(widget.activeCell.model.value.text.slice(0, 7)).to.equal(
          '###### '
        );
      });

it('should be clamped between 1 and 6', () => {
        NotebookActions.setMarkdownHeader(widget, -1);
        expect(widget.activeCell.model.value.text.slice(0, 2)).to.equal('# ');
        NotebookActions.setMarkdownHeader(widget, 10);
        expect(widget.activeCell.model.value.text.slice(0, 7)).to.equal(
          '###### '
        );
      });

it('should replace leading white space', () => {
        widget.activeCell.model.value.text = '      foo';
        NotebookActions.setMarkdownHeader(widget, 2);
        expect(widget.activeCell.model.value.text).to.equal('## foo');
      });

it('should be a no-op if there is no model', () => {
        widget.model = null;
        NotebookActions.setMarkdownHeader(widget, 1);
        expect(widget.activeCellIndex).to.equal(-1);
      });

it('should be a no-op if there is no model', () => {
        widget.model = null;
        NotebookActions.setMarkdownHeader(widget, 1);
        expect(widget.activeCellIndex).to.equal(-1);
      });

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

      if (current) {
        return NotebookActions.setMarkdownHeader(current.content, 1);
      }
    },
    isEnabled

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

      if (current) {
        return NotebookActions.setMarkdownHeader(current.notebook, 4);
      }
    },
    isEnabled

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

      if (current) {
        return NotebookActions.setMarkdownHeader(current.content, 4);
      }
    },
    isEnabled

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

      if (current) {
        return NotebookActions.setMarkdownHeader(current.notebook, 4);
      }
    },
    isEnabled

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

      if (current) {
        return NotebookActions.setMarkdownHeader(current.content, 6);
      }
    },
    isEnabled