### Question:
Accumulators { public static Reducer<Long, Long> longAdditionAccumulator() { return new Reducer<Long, Long>() { @Override public Long accumulate(Long accumulator, Long element) { return accumulator + element; } }; } private  Accumulators(); static Reducer<Integer, Integer> integerAdditionAccumulator(); static Reducer<Long, Long> longAdditionAccumulator(); static Reducer<Double, Double> doubleAdditionAccumulator(); static Reducer<Float, Float> floatAdditionAccumulator(); static Reducer<BigDecimal, BigDecimal> bigDecimalAdditionAccumulator(); static Reducer<BigInteger, BigInteger> bigIntegerAdditionAccumulator(); static Reducer<Integer, Integer> integerMultiplicationAccumulator(); static Reducer<Long, Long> longMultiplicationAccumulator(); static Reducer<BigInteger, BigInteger> bigIntegerMultiplicationAccumulator(); static Reducer<Double, Double> doubleMultiplicationAccumulator(); static Reducer<Float, Float> floatMultiplicationAccumulator(); static Reducer<BigDecimal, BigDecimal> bigDecimalMultiplicationAccumulator();  }### Answer:
@Test public void shouldReturnAnAccumulatorThatAddsTheSuppliedLongInputToTheSuppliedAccumulatorValue() throws Exception { Reducer<Long, Long> longAdditionAccumulator = Accumulators.longAdditionAccumulator(); Long result = longAdditionAccumulator.accumulate(10L, 5L); assertThat(result, is(15L)); }