### Question:
DefaultMetricsReader implements MetricsReader { private MetricValue readOperatorLatency() { MetricValue value = null; Timer operatorLatency = metricRegistry .timer(MetricName.OPERATOR_LATENCY.getName()); if (operatorLatency != null) { value = MetricValue.millis(Double.valueOf( operatorLatency.getSnapshot().getMean() / 1000000).intValue()); } return value; } DefaultMetricsReader(); @Override List<MetricName> readableNames(); @Override MetricValue readValue(MetricName name);  }### Answer:
@Test public void testReadOperatorLatency() { System.out.println("testReadOperatorLatency"); DefaultMetricsReader reader = new DefaultMetricsReader(); MetricValue value = reader.readValue(MetricName.OPERATOR_LATENCY); assertThat(value, notNullValue()); assertThat(value.getUnit(), equalTo(MetricUnit.MILLISECONDS)); assertThat(value.getValue(), greaterThanOrEqualTo(0.0)); }