@Override
  public Optional<WindowType> windowType() {
    return windowInfo.map(WindowInfo::getType);
  }
@Test
  public void shouldReturnWindowType() {
    // Given:
    givenWindowType(Optional.of(WindowType.TUMBLING));

    // Then:
    assertThat(materialization.windowType(), is(Optional.of(WindowType.TUMBLING)));
  }