public long cardinality() {
      HLLRepresentation representation = store();
      return representation == null ? 0 : representation.cardinality();
   }
@Test(dataProvider = "representations")
   public void testSingleThreadOperationsRepresentation(HLLRepresentation representation, long expected) {
      assertThat(representation.cardinality()).isEqualTo(0L);
      for (int i = 0; i < 1000; i++) {
         representation.set(("zt-" + i).getBytes(StandardCharsets.US_ASCII));
      }

      for (int i = 0; i < 1000; i++) {
         representation.set(("tt-" + i).getBytes(StandardCharsets.US_ASCII));
      }

      assertThat(representation.cardinality()).isEqualTo(expected);
   }