Mocking the HttpClient with NSubstitute

While reviewing some code I noticed that a project was using both Moq and NSubstitute. It seemed strange to me to use 2 mocking libraries in the same codebase.

Turned out that there was a problem when trying to combine IHttpClientFactory and NSubstitute. The reason is that the IHttpClientFactory returns a concrete type (HttpClient) and that NSubstitute cannot mock its methods (like SendAsync()).

The trick was to create your own HttpMessageHandler instead:

	public class FakeHttpMessageHandler : HttpMessageHandler
	{
	protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
	{
	return Task.FromResult(new HttpResponseMessage(HttpStatusCode.OK));
	}
	}

view raw FakeHttpMessageHandler.cs hosted with ❤ by GitHub

The mocking code became the following:

	var httpClientFactory = Substitute.For<IHttpClientFactory>();
	var httpClient = new HttpClient(new FakeHttpMessageHandler()) { BaseAddress=new Uri("https://localhost")};
	httpClientFactory.CreateClient(Arg.Any<string>()).Returns(httpClient);

view raw NSubstitute.cs hosted with ❤ by GitHub