public void test_containsAll2() {
   ExternalIdSearch test = ExternalIdSearch.of(_id11, _id12);
   assertEquals(true, test.containsAll(ImmutableSet.of(_id11, _id12)));
   assertEquals(true, test.containsAll(ImmutableSet.of(_id11)));
   assertEquals(true, test.containsAll(ImmutableSet.of(_id12)));
   assertEquals(false, test.containsAll(ImmutableSet.of(_id21)));
   assertEquals(true, test.containsAll(ImmutableSet.of()));
 }
 @Test(expectedExceptions = IllegalArgumentException.class)
 public void test_containsAll_null() {
   ExternalIdSearch test = ExternalIdSearch.of(_id11, _id12);
   test.containsAll(null);
 }