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