### Question:
SumFunction extends AggregateFunction<JsonNode, Double> { @Override public Double compute() { return sum; }  @Override AggregateFunction addValue(JsonNode value); @Override Double compute(); @Override AggregateFunction<JsonNode, Double> merge(AggregateFunction<JsonNode, Double> newValue);  }### Answer:
@Test public void shouldReturnZeroWhenNoValue() { SumFunction sumFunction =new SumFunction(); assertThat(sumFunction.compute()).isEqualTo(0); }