If you have an HTTP Client unit test, you can try the option of making a Wrapper interface in your solution like this here: http://stackoverflow.com/questions/10693955/stubbing-or-mocking-asp-net-web-api-httpclient. As for two parameters in the unit test, you can do the following..
Guid id = Guid.NewGuid(); string baseUri = ConfigurationManager.AppSettings["BaseUrl"] + @"/" + ConfigurationManager.AppSettings["ApiVersion"] + @"/"; Dto responseDto = new Dto(); httpClient.Setup(x => x.PostAsync(new Uri(baseUri + "AdditionalUrlHere/Stuff"), It.IsAny ())) .Callback ((uri, dto) => responseDto = dto) .ReturnsAsync(id);