public void PostsToTheCorrectUrl()
        {
            var connection = Substitute.For<IApiConnection>();
            var client = new GistsClient(connection);

            var newGist = new NewGist();
            newGist.Description = "my new gist";
            newGist.Public = true;

            newGist.Files.Add("myGistTestFile.cs", "new GistsClient(connection).Create();");
            
            client.Create(newGist);

            connection.Received().Post<Gist>(Arg.Is<Uri>(u => u.ToString() == "gists"), Arg.Any<object>());
        }