public void allowSleepCalls(int numCalls) {
    sleepCallsAllowed.updateAndGet(prev -> prev == null ? new Semaphore(0) : prev).release(numCalls);
  }
Give permission to allow {@code numCalls} sleep calls to proceed unblocked. Calling this for the first time enables
the feature. If this method is never called, sleep calls proceed unblocked.
@param numCalls the number of sleep calls to allow.
ambry-test-utils/src/main/java/com/github/ambry/utils/MockTime.java