DataflowElementExecutionTracker extends ElementExecutionTracker { @Override public void exit() { executionWriter.doneProcessing(); } private  DataflowElementExecutionTracker(CounterFactory counterFactory); static ElementExecutionTracker create(
      CounterFactory counterFactory, PipelineOptions options); @Override void enter(NameContext step); @Override void exit(); @Override void takeSample(long millisSinceLastSample); @VisibleForTesting
  static final String TIME_PER_ELEMENT_EXPERIMENT; }
@Test public void testThrowsOnExitBeforeEnter() { thrown.expect(IllegalStateException.class); tracker.exit(); }