LinearId implements Id { @Override public int getCount() { return data_ == null ? 0 : data_.length; } LinearId();  LinearId(String id);  LinearId(String parent, String tail);  LinearId(String... id);  LinearId(String[] ids, IdAggregator aggregator); private  LinearId(String[] ids, IdAggregator aggregator, Void private_constructor); @NonNull static LinearId of(@NonNull Id id); @Override String get(int index); @Override LinearId extend(String tail); @Override LinearId parent(); @Override int getCount(); @Override boolean equals(Object obj); @Override int hashCode(); @Override String toString(); @Override String[] toArray();  }
@Test public void testGetCount() { assertThat(empty.getCount()).isEqualTo(0); assertThat(single.getCount()).isEqualTo(1); assertThat(dual.getCount()).isEqualTo(2); }