async createTestSpreadsheet() {
    const res = await this.sheetsService.spreadsheets.create({
      resource: {
        properties: {
          title: 'Test Spreadsheet',
        },
      },
      fields: 'spreadsheetId',
    });
    this.deleteFileOnCleanup(res.data.spreadsheetId);
    return res.data.spreadsheetId;
  }
Creates a test Spreadsheet.
@return {Promise} A promise to return the Google API service.