異步單元測試與便攜式類庫

Question

我有一個可移植的類庫，需要至少針對.net 4.5和Silverlight 5.我遇到了一個問題，試圖在VS 2012編寫MSTest單元測試，因爲我的庫沒有使用新的異步/等待範例。有什麼辦法可以測試這種方法嗎？

public static void Get(string uri, string acceptHeader, Action<string> callback) 
{ 
    var request = (HttpWebRequest)WebRequest.Create(uri); 
    request.Accept = acceptHeader;   

    request.BeginGetResponse(o => 
    { 
     var r = o.AsyncState as HttpWebRequest; 
     try 
     { 
      var response = r.EndGetResponse(o); 
      using (var sr = new StreamReader(response.GetResponseStream())) 
      { 
       callback(sr.ReadToEnd()); 
      } 
     } 
     catch (Exception ex) 
     { 
      throw new WebException(string.Format("Unable to access {0}", uri), ex); 
     } 
    }, request); 
} 

Answer 1

首先，我建議你重新考慮async/await。這是未來的潮流。 Microsoft.Bcl.Async爲以.NET 4.5和SL5爲目標的可移植庫提供了支持async。

但是，如果你不想做，你仍然可以使用async單元測試：

[TestMethod] 
public async Task Get_RetrievesExpectedString() 
{ 
    var tcs = new TaskCompletionSource<string>(); 
    var client = new ... // arrange 

    client.Get(uri, acceptHeader, result => 
    { 
    tcs.SetResult(result); 
    }); 
    var actual = await tcs.Task; 

    Assert.AreEqual(expected, actual); 
} 

或者，如果你願意，你可以做「老派」：

[TestMethod] 
public void Get_RetrievesExpectedString() 
{ 
    var mre = new ManualResetEvent(initialState: false); 
    string actual = null; 
    var client = new ... // arrange 

    client.Get(uri, acceptHeader, result => 
    { 
    actual = result; 
    mre.Set(); 
    }); 
    mre.WaitOne(); 

    Assert.AreEqual(expected, actual); 
} 

Answer 2

只是無法抗拒重構代碼。你可以在你可以做一天的末尾使用封閉做到以下幾點

public static void Get(string uri, string acceptHeader, Action<string> callback) 
{ 
    var request = (HttpWebRequest)WebRequest.Create(uri); 
    request.Accept = acceptHeader;   

    request.BeginGetResponse(o => 
    { 
     try 
     { 
      var response = request.EndGetResponse(o); 
      using (var sr = new StreamReader(response.GetResponseStream())) 
      { 
       callback(sr.ReadToEnd()); 
      } 
     } 
     catch (Exception ex) 
     { 
      throw new WebException(string.Format("Unable to access {0}", uri), ex); 
     } 
    }, null); 
} 

但是以下

public async static void Get(string uri, string acceptHeader, Action<string> callback) 
{ 
    var request = (HttpWebRequest)WebRequest.Create(uri); 
    request.Accept = acceptHeader;   
    var response = await Task.Factory.FromAsync(
          request.BeginGetRequestStream , 
          request.EndGetRequestStream , 
          uri, 
          null); 
    using (var sr = new StreamReader(response)) 
    { 
     callback(sr.ReadToEnd()); 
    } 
} 

好了，所以這裏是我會怎麼做

void Main() 
{ 
    {...} 
    var request = (HttpWebRequest)WebRequest.Create(uri); 
    request.Accept = acceptHeader; 
    var response = await request.DownloadStringTaskAwait(); 
    DoSomeStuff(response); 
} 

// Define other methods and classes here 
public static class HttpWebRequestExtension 
{ 
    public async Task<string> DownloadStringTaskAwait(this HttpWebRequest request) 
    { 
     var response = await Task.Factory.FromAsync<Stream>(
          request.BeginGetRequestStream, 
          request.EndGetRequestStream, 
          null); 
        using (var sr = new StreamReader(response)) 
        { 
         return sr.ReadToEnd(); 
        } 
      } 

}