public void Empty_list_is_mapped()
            {
                Func <int, string> map = i => i.ToString();

                var elevatedMap = ListExtensions.FMap(map);

                Assert.Equal(new List <string>(), elevatedMap(new List <int>()));
            }
            public void Elements_are_mapped()
            {
                Func <int, string> map = i => i.ToString();

                var elevatedMap = ListExtensions.FMap(map);

                Assert.Equal(
                    new List <string> {
                    map(1), map(2), map(3)
                },
                    elevatedMap(new List <int> {
                    1, 2, 3
                }));
            }