@Override
  public NestedFieldFilterScope<T> getFilterScope() {
    return filterScope;
  }
@Test
  public void getFilterScope_always_returns_the_same_instance() {
    String fieldName = randomAlphabetic(5);
    String nestedFieldName = randomAlphabetic(6);
    String value = randomAlphabetic(7);
    boolean sticky = RANDOM.nextBoolean();
    NestedFieldTopAggregationDefinition<String> underTest = new NestedFieldTopAggregationDefinition<>(fieldName + "." + nestedFieldName, value, sticky);

    Set<TopAggregationDefinition.FilterScope> filterScopes = IntStream.range(0, 2 + RANDOM.nextInt(200))
      .mapToObj(i -> underTest.getFilterScope())
      .collect(Collectors.toSet());

    assertThat(filterScopes).hasSize(1);
  }