async createTestTextbox(presentationId, pageObjectId) {
    const boxId = 'MyTextBox_01';
    const pt350 = {
      magnitude: 350,
      unit: 'PT',
    };
    const requests = [
      {
        createShape: {
          objectId: boxId,
          shapeType: 'TEXT_BOX',
          elementProperties: {
            pageObjectId,
            size: {
              height: pt350,
              width: pt350,
            },
            transform: {
              scaleX: 1,
              scaleY: 1,
              translateX: 350,
              translateY: 100,
              unit: 'PT',
            },
          },
        },
      },
      {
        insertText: {
          objectId: boxId,
          insertionIndex: 0,
          text: 'New Box Text Inserted',
        },
      },
    ];
    const res = await this.slidesService.presentations.batchUpdate({
      presentationId,
      resource: {
        requests,
      },
    });
    return res.data.replies[0].createShape.objectId;
  }
Creates a test textbox
@param  {string}   presentationId The presentation ID.
@param  {string}   pageObjectId   The element page object ID.
@return {Promise<string>} The textbox's object ID.