@Override
  public <T> Gauge<T> newGauge(String group, Gauge<T> gauge) {
    if (!gauges.containsKey(group)) {
      gauges.put(group, new ArrayList<>());
    }
    gauges.get(group).add(gauge);
    return gauge;
  }
retrieves the Map of Timers
@return timers
samza-sql/src/test/java/org/apache/samza/sql/util/TestMetricsRegistryImpl.java