public async Task EnsuresArgumentsNotNull()
        {
            var connection = Substitute.For<IApiConnection>();
            var client = new GistsClient(connection);

            Assert.Throws<ArgumentNullException>(() => client.Delete(null));
        }
        public void PostsToTheCorrectUrl()
        {
            var connection = Substitute.For<IApiConnection>();
            var client = new GistsClient(connection);

            client.Delete("1");

            connection.Received().Delete(Arg.Is<Uri>(u => u.ToString() == "gists/1"));
        }