public async Task DownloadFile() { var mock = new Mock <IWebClientHelper>(); var timeline = new TimelineService(BaseUrl, "ABC", "123", "cache", mock.Object); await timeline.DownloadFileAsync("http://www.upload.com/url", "testfilename.docx"); mock.Verify(m => m.DownloadFileAsync("http://www.upload.com/url", "testfilename.docx")); }