createTestDocument() {
    return this.createFile(
        {
          name: 'Test Document',
          mimeType: 'application/vnd.google-apps.document',
        },
        {
          mimeType: 'text/plain',
          body: fs.createReadStream('files/document.txt'),
        },
    );
  }
Creates a test Google Docs document.
@return {Promise} A promise to return the Google Drive file.