### Question:
Iterators { public static int failFast1() { ArrayList<Integer> numbers = new ArrayList<>(); numbers.add(10); numbers.add(20); numbers.add(30); numbers.add(40); Iterator<Integer> iterator = numbers.iterator(); while (iterator.hasNext()) { Integer number = iterator.next(); numbers.add(50); } return numbers.size(); }  static int failFast1(); static int failFast2(); static int failSafe1();  }### Answer:
@Test public void whenFailFast_ThenThrowsException() { assertThatThrownBy(() -> { failFast1(); }).isInstanceOf(ConcurrentModificationException.class); }