### Question:
IdStack implements Iterable<String> { public boolean isEmpty() { return deque.isEmpty(); }  void push(String id, E item); E peek(); E pop(); boolean isEmpty(); int size(); String peekId(); void clear(); E get(final String id); boolean containsId(final String id); E remove(final String id); boolean isTop(final String id); @NonNull @Override Iterator<String> iterator(); Collection<E> values();  }### Answer:
@Test public void isEmpty() throws Exception { assertThat(uut.isEmpty()).isTrue(); uut.push("123", 123); assertThat(uut.isEmpty()).isFalse(); }