public async void DownloadFileAsync()
        {
            var url      = "https://www.baidu.com/img/baidu_jgylogo3.gif";
            var filePath = @"d:\baidu_jgylogo3.gif";

            File.Delete(filePath);

            var combiner = await _fileTransfer.DownloadFileAsync(url, filePath).ConfigureAwait();

            Assert.NotNull(combiner);
            Assert.True(combiner.Exists());

            combiner.Delete();
            Assert.False(combiner.Exists());
        }