code: public int getNumFaultyTrackers() {
      int count = 0;
      synchronized (this) {
        for (String trackerName : usageReports.keySet()) {
          if (isFaulty(trackerName)) {
            count++;
          }
        }
      }
      return count;
    }
docs: Get the number of faulty trackers.
  @return the number of faulty trackers.