    @Test
    public void testMap() {

        // Given a list
        List<Integer> list = itemList(1, 2, 3);

        // When an increment function is mapped across it
        List<Integer> result = list.map(i -> i + 1);

        // Then each of the elements is incremented
        assert(result.equals(itemList(2, 3, 4)));
    }