How to use the @jupyterlab/cells.MarkdownCellModel function in @jupyterlab/cells

it('should be set with type "markdown"', () => {
        const model = new MarkdownCellModel({});
        expect(model.type).to.equal('markdown');
      });
    });

it('should be set with type "markdown"', () => {
        const model = new MarkdownCellModel({});
        expect(model.type).to.equal('markdown');
      });
    });

describe('MarkdownCellWidget', () => {

    let contentFactory = createBaseCellFactory();
    let model = new MarkdownCellModel({});

    describe('#constructor()', () => {

      it('should create a markdown cell widget', () => {
        let widget = new MarkdownCellWidget({ model, rendermime, contentFactory });
        expect(widget).to.be.a(MarkdownCellWidget);
      });

      it('should accept a custom contentFactory', () => {
        let widget = new MarkdownCellWidget({ model, rendermime, contentFactory });
        expect(widget).to.be.a(MarkdownCellWidget);
      });

      it('should set the default mimetype to text/x-ipythongfm', () => {
        let widget = new MarkdownCellWidget({ model, rendermime, contentFactory });
        expect(widget.model.mimeType).to.be('text/x-ipythongfm');

it('should be set with type "markdown"', () => {
        let model = new MarkdownCellModel({});
        expect(model.type).to.be('markdown');
      });

createMarkdownCell(options: CellModel.IOptions): IMarkdownCellModel {
      if (this.modelDB) {
        if (!options.id) {
          options.id = UUID.uuid4();
        }
        options.modelDB = this.modelDB.view(options.id);
      }
      return new MarkdownCellModel(options);
    }

private _createMarkdownCellOptions(text: string = ''): MarkdownCell.IOptions {
    let contentFactory = this.contentFactory.markdownCellContentFactory;
    let model = new MarkdownCellModel({ });
    this._disposables.add(model);
    let rendermime = this._rendermime;
    model.value.text = text || '';
    return { model, rendermime, contentFactory };
  }

createMarkdownCell(options: CellModel.IOptions): IMarkdownCellModel {
      if (this.modelDB) {
        if (!options.id) {
          options.id = UUID.uuid4();
        }
        options.modelDB = this.modelDB.view(options.id);
        let cell;
        this.modelDB.withTransaction(() => {
          cell = new MarkdownCellModel(options);
        });
        return cell;
      }
      return new MarkdownCellModel(options);
    }

private _createMarkdownCellOptions(text: string = ''): MarkdownCell.IOptions {
    let contentFactory = this.contentFactory.markdownCellContentFactory;
    let model = new MarkdownCellModel({ });
    this._disposables.add(model);
    let rendermime = this._rendermime;
    model.value.text = text || '';
    return { model, rendermime, contentFactory };
  }