public void test_withExternalIdsAdded_iterable() {
   ExternalIdSearch base = ExternalIdSearch.of(ExternalId.of("A", "B"));
   assertEquals(1, base.size());
   ExternalIdSearch test =
       base.withExternalIdsAdded(Arrays.asList(ExternalId.of("A", "C"), ExternalId.of("D", "E")));
   assertEquals(1, base.size());
   assertEquals(3, test.size());
   assertTrue(test.getExternalIds().contains(ExternalId.of("A", "B")));
   assertTrue(test.getExternalIds().contains(ExternalId.of("A", "C")));
   assertTrue(test.getExternalIds().contains(ExternalId.of("D", "E")));
 }
 public void test_withExternalIdsAdded_iterable_null() {
   ExternalIdSearch test = ExternalIdSearch.of(ExternalId.of("A", "B"));
   assertThrows(
       () -> test.withExternalIdsAdded((Iterable<ExternalId>) null),
       IllegalArgumentException.class);
 }