@Override
  public Counter newCounter(String group, Counter counter) {
    if (!counters.containsKey(group)) {
      counters.put(group, new ArrayList<>());
    }
    counters.get(group).add(counter);
    return counter;
  }
TestMetricsRegistryImpl implements the MetricRegistry interface and adds get APIs
for testing Translators.
samza-sql/src/test/java/org/apache/samza/sql/util/TestMetricsRegistryImpl.java