@Override
  public void setRegionUsage(Map<RegionInfo, Long> regionUsage) {
    wlock.lock();
    try {
      this.regionUsage = Objects.requireNonNull(regionUsage);
    } finally {
      wlock.unlock();
    }
  }
Fetches the namespace quota. Visible for mocking/testing.
hbase-server/src/main/java/org/apache/hadoop/hbase/quotas/NamespaceQuotaSnapshotStore.java