this.queue = new ArrayBlockingQueue<>(1);
      assertTrue(queue.offer("blocksPutCallsUntilRemoved"));
      this.completed = new Completion(countdownInMillis);
      scheduleEnableWrites(this.queue, countdownInMillis);
    }

    /** Perform a {@code put} and assert that operation completed in the expected timeframe. */
    void putSuccessfully() {
      putUninterruptibly(queue, "");