如何在Windows Phone上对使用Web服务的方法进行单元测试？

Question

I'm working on a project that retrieves information from an external webservice API, but I'm not sure how I'm supposed to test it, I'm quite new at Testing and I have done just a couple of Unit Test, but as far as I know I have to mock the webservice functionality, I've been looking for info regarding this subject but haven't found anything for Windows Phone yet. What's the standard procedure for these type of cases?

Here's a simple version of what I want to test:

    public async Task<List<Song>> FetchSongsAsync(String query)
    {
        if (String.IsNullOrEmpty(query))
            return null;

        string requestUrl = "webservice url";
        var client = new HttpClient();
        var result = await client.GetStringAsync(new Uri(requestUrl,UriKind.Absolute));
        try
        {
            var result = JsonConvert.DeserializeObject<RootObject>(result);
            return result;
        }
        catch (Exception)
        {
            return null;
         }
    }

Thanks!

Answer 1

Decouple your code from its dependencies: make content loading and its deserialization replaceable :

private readonly IClient client;
private readonly ISerializer serializer;

public YourService(IClient client, ISerializer serializer)
{
    _client = client;
    _serializer = serializer;
}

public async Task<List<Song>> FetchSongsAsync(String query)
{
    try
    {
        var result = await _client.GetStringAsync(new Uri("http://example.com"));
        return _serializer.DeserializeObject<RootObject>(result);
    }
    catch (Exception)
    {
        return null;
    }
}

Answer 2

The first thing that may help is understand and use dependency injection. Basically taking any dependencies of your object/method/etc and (as it states) injecting them into the object/method/etc. For example, you are having a difficult time figuring out how to test the method because the method depends on being able to access the web service. There are a couple things you can do after this.

One thing to do is to check out mocking frameworks such as Moq .

Another thing I recently did was I added an overloaded constructor (dependency injection) that takes a HttpMessageInvoker object (note HttpClient derives from this). This way I could instantiate the class with my own response message:

public class MyLoader()
{
    protected HttpMessageInvoker MessageInvoker { get; set; }
    private HttpRequestMessage requestMessage;

    public MyLoader()    // default constructor
    {
        MessageInvoker = new HttpClient();
    }

    public MyLoader(HttpMessageInvoker httpMessageInvoker)
    {
        MessageInvoker = httpMessageInvoker;
    }

    public object DoSomething()
    {
        var response = await MessageInvoker.SendAsync(requestMessage, cancellationTokenSource.Token);
    }

Here is my mock message invoker:

public class MockMessageInvoker : HttpMessageInvoker
{
    public string ResponseString { get; set; }

    public MockMessageInvoker(string responseString)
        : base(new HttpClientHandler())
    {
        ResponseString = responseString;
    }

    public override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
    {
        return Task.Run<HttpResponseMessage>(() =>
        {
            HttpResponseMessage responseMessage = new HttpResponseMessage(
                System.Net.HttpStatusCode.OK);

            var bytes = Encoding.ASCII.GetBytes(ResponseString);
            var stream = new System.IO.MemoryStream(bytes);

            responseMessage.Content = new StreamContent(stream);
            return responseMessage;
        });

    }
}

I can call it all like so:

MyLoader loader = new MyLoader(new MockMessageInvoker(validJsonResponse));
loader.DoSomething() // I've removed the dependency on the service and have control of the content in the response

It's quick and dirty, but does the trick.

Hope this helps.