@Override
    public boolean evaluate() throws Exception {
      SpaceQuotaSnapshot snapshot;
      if (null == ns) {
        snapshot = (SpaceQuotaSnapshot) conn.getAdmin().getCurrentSpaceQuotaSnapshot(tn);
      } else {
        snapshot = (SpaceQuotaSnapshot) conn.getAdmin().getCurrentSpaceQuotaSnapshot(ns);
      }

      LOG.debug("Saw quota snapshot for " + (null == tn ? ns : tn) + ": " + snapshot);
      if (null == snapshot) {
        return false;
      }
      return evaluate(snapshot);
    }
Abstraction to simplify the case where a test needs to verify a certain state on a
{@code SpaceQuotaSnapshot}. This class fails-fast when there is no such snapshot obtained from
the Master. As such, it is not useful to verify the lack of a snapshot.
hbase-server/src/test/java/org/apache/hadoop/hbase/quotas/SpaceQuotaHelperForTests.java