new ImmutableRangeMap.Builder<Integer, Integer>().put(rangeOne, 1).put(rangeTwo, 6).build();
    CollectorTester.of(
            ImmutableRangeMap.<Range<Integer>, Integer, Integer>toImmutableRangeMap(
                k -> k, k -> k.lowerEndpoint()))
        .expectCollects(rangeMap, rangeOne, rangeTwo);
  }