title: TumblingProcessingTimeWindows processing with event time characteristic is not triggered
body: <p>My use-case is quite simple I receive events that contain "event timestamp", and want them to be aggregated based on event time. and the output is a periodical processing time tumbling window every 10min. </p>
  
  <p>More specific, the stream of data that is keyed and need to compute counts for 7 seconds.</p>
  
  <ol>
  <li>a tumbling window of 1 second</li>
  <li>a sliding window for counting 7 seconds with an advance of 1 second </li>
  <li>a windowall to output all counts every 1s</li>
  </ol>
  
  <p>I am not able to integration test it (i.e., similar to unit test but an end-to-end testing) as the input has fake event time, which won't trigger </p>
  
  <p>Here is my snippet</p>
  
  <pre><code>env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime)
  
  val oneDayCounts = data
    .map(t =&gt; (t.key1, t.key2, 1L, t.timestampMs))
    .keyBy(0, 1)
    .timeWindow(Time.seconds(1))
    .sum(2)
  
  val sevenDayCounts = oneDayCounts
    .keyBy(0,1)
    .timeWindow(Time.seconds(3), Time.seconds(1))
    .sum(2)
  
  // single reducer
  sevenDayCounts
    .windowAll(TumblingProcessingTimeWindows.of(Time.seconds(1)))
    .process(...)
  </code></pre>
  
  <p>I use EventTime as timestamp and set up an integration test code with <code>MiniClusterWithClientResource</code>. also created some fake data with some event timestamp like 1234l, 4567l, etc.</p>
  
  <p>EventTimeTrigger is able to be fired for sum computation but the following TumblingProcessingTimeWindow is not able to trigger. I had a Thread.sleep of 30s in the IT test code but still not triggered after the 30s</p>