@VisibleForTesting
  List<Page> getAllPages() {
    return requireNonNull(pages, "Pages haven't been initialized yet");
  }
@Test
  public void fail_if_pages_called_before_server_startup() {
    assertThatThrownBy(() -> underTest.getAllPages())
      .isInstanceOf(NullPointerException.class)
      .hasMessageContaining("Pages haven't been initialized yet");
  }