@Override
          public <T> void gauge(Gauge<T> gauge) {
            Double num = (Double) gauge.getValue();
            Assert.assertNotEquals(0D, (Double) gauge.getValue(), 0.0001);
          }
Make sure that the histograms can record the key value size and we can use a
{@link MetricsVisitor} to get access to the value store in the histograms
samza-test/src/test/java/org/apache/samza/storage/kv/TestKeyValueSizeHistogramMetric.java