[c#] Mocking HttpClient in unit tests

You could use RichardSzalay MockHttp library which mocks the HttpMessageHandler and can return an HttpClient object to be used during tests.

GitHub MockHttp

PM> Install-Package RichardSzalay.MockHttp

From the GitHub documentation

MockHttp defines a replacement HttpMessageHandler, the engine that drives HttpClient, that provides a fluent configuration API and provides a canned response. The caller (eg. your application's service layer) remains unaware of its presence.

Example from GitHub

 var mockHttp = new MockHttpMessageHandler();

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

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

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

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

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