ASP.NET Core mock HttpClient with custom HttpClientHandler

Question

I have trouble mocking with Moq. Normally having a HttpClient I would mock it by injecting the HttpClient in the base class like this:

public class MyClass
{
    private readonly HttpClient httpClient;

    public MyClass(HttpClient httpClient)
    {
        this.httpClient = httpClient;
    }
}

But now I have different functions in my class MyClass that need a custom HttpClientHandler like this:

HttpClientHandler httpClientHandler = new HttpClientHandler();
...
using var client = new HttpClient(httpClientHandler);

If I'd simply inject a HttpClient in MyClassTest with var service = new MyClass(httpMock.Object);, then the httpClient would be overwritten.

What would be the right way to test my functions and not making a real HTTP-call?

You should look in to IHttpClientFactory and typed/named HttpClient injection. — Andy
– Andy, Commented Nov 13, 2020 at 22:35
1) Create a test-only overload where you can pass in a custom handler. I've used this approach with great success for years. 2) Abstract the class to an HttpClient and inject that instead. In theory your abstractions should be designed to interfaces and you can hide the fact they even use HTTP. — No Refunds No Returns
– No Refunds No Returns, Commented Nov 13, 2020 at 23:26
I went with public MyClass(HttpClientHandler httpClientHandler = null) and then called it with a mock: var mockHttpMessageHandler = new Mock<HttpClientHandler>();. It does the job, I'm just not sure, how "clean" or "best practice" it is. — user3079834
– user3079834, Commented Nov 15, 2020 at 16:00

Peter Csala · Accepted Answer · 2020-11-16 08:50:56Z

1

I suppose you are using typed client approach of the IHttpClientFactory. That's why your MyClass ctor receives an HttpClient instance.

If you need to mock that HttpClient then I suggest you to follow Hamid Mosalla's advice.

In short there is a helper class, which makes HttpMessageHandler's SendAsync mockable (without the need to use the Moq.Protected).

public class FakeHandler: HttpMessageHandler
{
    public virtual HttpResponseMessage Send(HttpRequestMessage request)
    {
        throw new NotImplementedException();
    }

    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        return Task.FromResult(Send(request));
    }
}

You can use this helper class like this to mock any HttpClient call:

var httpResponse = new HttpResponseMessage
{
    Content = new StringContent(JsonConvert.SerializeObject(responseObject))
};

var mockHandler = new Mock<FakeHandler> { CallBase = true };
mockHandler
    .Setup(handler => handler.Send(It.IsAny<HttpRequestMessage>()))
    .Returns(httpResponse);

var mockHttpClient = new HttpClient(mockHandler.Object);
var SUT = new MyClass(mockHttpClient);

answered Nov 16, 2020 at 8:50

Peter Csala

23.7k16 gold badges51 silver badges96 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

user3079834 Over a year ago

This is the same approach that @Andy suggested. I'll definitely have a look into this, when I have more time as this seems more "clean".

belgaard · Accepted Answer · 2020-11-17 09:53:01Z

1

What would be the right way to test my functions and not making a real HTTP-call?

Maybe not what you are looking for, but I suggest you consider Andrew Lock's wisdom - don't unit-test API/MVC controllers in ASP.NET Core.

For .NET Core (and .NET 5) you should avoid mocking HttpClient if you are testing a controller class.

If a controller class is not your SUT, I would wrap the HttpClient in a facade interface and mock that.

answered Nov 17, 2020 at 9:53

belgaard

214 bronze badges

1 Comment

user3079834 Over a year ago

Well I am testing the underlying Service Class to the Controller. Like fetching and processing data from another page. The result is then given to the Controller. The controller itself is tested against the mocked interface of the Service Layer. The Service Class should be tested in my opinion and to do that I need the HttpClient-mock

Collectives™ on Stack Overflow

ASP.NET Core mock HttpClient with custom HttpClientHandler

2 Answers 2

1 Comment

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related