How to pass in a mocked HttpClient in a .NET test?



Answers

I know that this is an old question but I stumbled with it during a search on this topic and found a very nice solution to make testing HttpClient easier.

It is available via nuget:

https://github.com/richardszalay/mockhttp

PM> Install-Package RichardSzalay.MockHttp

Here is a quick look on the usage:

var mockHttp = new MockHttpMessageHandler();

// Setup a respond for the user api (including a wildcard in the URL)
mockHttp.When("http://localost/api/user/*")
        .Respond("application/json", "{'name' : 'Test McGee'}"); // Respond with JSON

// Inject the handler or client into your application code
var client = new HttpClient(mockHttp);

var response = await client.GetAsync("http://localost/api/user/1234");
// or without await: var response = client.GetAsync("http://localost/api/user/1234").Result;

var json = await response.Content.ReadAsStringAsync();

// No network connection required
Console.Write(json); // {'name' : 'Test McGee'}

More info on the github project page. Hope this can be useful.

Question

I have a service which uses Microsoft.Net.Http to retrieve some Json data. Great!

Of course, I don't want my unit test hitting the actual server (otherwise, that's an integration test).

Here's my service ctor (which uses dependency injection...)

public Foo(string name, HttpClient httpClient = null)
{
...
}

I'm not sure how I can mock this with ... say .. Moq or FakeItEasy.

I want to make sure that when my service calls GetAsync or PostAsync .. then i can fake those calls.

Any suggestions how I can do that?

I'm -hoping- i don't need to make my own Wrapper .. cause that's crap :( Microsoft can't have made an oversight with this, right?

(yes, it's easy to make wrappers .. i've done them before ... but it's the point!)




You can use classes instead of interfaces with both Moq and Rhino.Mocks, but the mocked methods must be virtual. Mark Rushakoff's answer on TypeMock is correct (+1).

The best option is to refactor your existing code for testability (which may take time). I'd recommend reading Working Effectively with Legacy Code by Michael Feathers.




Use the Decorator or Interceptor pattern.

Example concrete decorator:

public class CustomDelegatingHandlerTokenRefresher() : DelegatingHandler
{
    public CustomDelegatingHandlerTokenRefresher(DelegatingHandler handler)
    {
        InnerHandler = handler;
    }

    protected override async Task<HttpResponseMessage> SendAsync(
      HttpRequestMessage request, CancellationToken cancellationToken)
    {
        RefreshToken();
        return await InnerHandler.SendAsync(request, cancellationToken);
    }
}



You can use Flurl instead of currently used HttpClient. It has testing capabilities. http://tmenier.github.io/Flurl/testable-http/, E.g.

using (var httpTest = new HttpTest()) {
        // Flurl is now in test mode 
       sut.CallThingThatUsesFlurlHttp(); // HTTP calls are faked!
}



Non Interface dependent Mocking Frameworks for C#

Microsoft Research has developed Moles for this, which is a part of Pex but can be installed independently. And it's free. There's a good introductory article (pdf) on the website that explains how to mock a static method. It takes some time before they get to the stuff you want (page 16, Task 3).

Here and here (Channel 9) you can find an example on how to stub DateTime.Now. Using Moles, you can mock anything you want.




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