public void DownloadAsyncTest()
{
// Arrange
string filePath = String.Empty;
string url = "http://somepage.com";
var webClientStub = MockRepository.GenerateStub<WebClient>();
// Act
var wd = new WebDownloader(webClientStub);
wd.DownloadAsync(filePath, url, (o,e)=> {});
// Assert
webClientStub.AssertWasCalled(wc => wc.DownloadFileAsync(Arg<Uri>.Is.Equal(new Uri(url)), Arg<String>.Is.Equal(filePath)));
}