CollectorTester.of(collector)
        .expectCollects(ImmutableTable.of())
        .expectCollects(ImmutableTable.of("one", "uno", 1), immutableCell("one", "uno", 1));
  }

  public void testToImmutableTableMergingSanityTest() {
    Collector<Cell<String, String, Integer>, ?, ImmutableTable<String, String, Integer>> collector =
        toImmutableTable(Cell::getRowKey, Cell::getColumnKey, Cell::getValue, Integer::sum);