@Test
public void testGetTermChildrenId4andId1() {

  // id4 has only one child term, id1: id1->id4
  Set<TermId> expected = ImmutableSet.of(id4, id1);
  assertEquals(expected, getChildTerms(ontology, id4));
  // id1 is a leaf term and thus has no children
  expected = ImmutableSet.of(id1);
  assertEquals(expected, getChildTerms(ontology, id1));
}