Unit tests for HttpClient using HttpMessageHandler

You can unit test a class that uses HttpClient by giving that HttpClient a mock HttpMessageHandler. This way, you can capture the request and prevent it from actually going over the wire.

Here is an example using Moq. HttpClient depends on HttpMessageHandler’s SendAsync() method, so give SendAsync() a stub implementation and use Moq’s Callback() to capture arguments.

var handler = new Mock<HttpMessageHandler>();

handler.Protected()

    .Setup<Task<HttpResponseMessage>>("SendAsync", ItExpr.IsAny<HttpRequestMessage>(), ItExpr.IsAny<CancellationToken>())

    .Returns(Task<HttpResponseMessage>.Factory.StartNew(() =>

    {

        return new HttpResponseMessage(HttpStatusCode.OK);

    }))

    .Callback<HttpRequestMessage, CancellationToken>((r, c) =>

    {

        Assert.AreEqual(HttpMethod.Get, r.Method);

    });

 

using (var client = new HttpClient(handler.Object))

{

    var request = new HttpRequestMessage(HttpMethod.Get, "http://www.google.com");

    var response = client.SendAsync(request).Result;

    Console.WriteLine(response.StatusCode);

}