@Override
  public void addChildren(Deque<Expression> expressions) {
    if (expression != null) {
      expression.addChildren(expressions);
    }
  }
@Test
  public void addChildren() {
    @SuppressWarnings("unchecked")
    Deque<Expression> expressions = mock(Deque.class);
    test.addChildren(expressions);
    verify(expr).addChildren(expressions);
    verifyNoMoreInteractions(expr);
  }