assertEquals("google.com", InternetDomainName.from("www.google.com").parent().toString());

    assertThrows(IllegalStateException.class, () -> InternetDomainName.from("com").parent());
  }

  public void testChild() {
    InternetDomainName domain = InternetDomainName.from("foo.com");

    assertEquals("www.foo.com", domain.child("www").toString());

    assertThrows(IllegalArgumentException.class, () -> domain.child("www."));