@Test
public void testCartesianProduct() {

    Poset<String> one23 = new Poset<>(new ArrayList<>(Arrays.asList("1", "2", "3")));
    List<Poset<String>> product = Poset.cartesianProduct(ABC, one23);
    assertEquals(product.size(), 9);
    assertEquals(product.get(0), new Poset(new ArrayList<>(Arrays.asList("a", "1"))));
    assertEquals(product.get(8), new Poset(new ArrayList<>(Arrays.asList("c", "3"))));        
}