@Override
  public String toString() {
    StringBuilder builder = new StringBuilder("AfterProcessingTime.pastFirstElementInPane()");
    for (SerializableFunction<Instant, Instant> delayFn : timestampMappers) {
      builder.append(".plusDelayOf(").append(delayFn).append(")");
    }

    return builder.toString();
  }
@Test
  public void testToString() {
    TriggerStateMachine trigger = AfterProcessingTimeStateMachine.pastFirstElementInPane();
    assertEquals("AfterProcessingTime.pastFirstElementInPane()", trigger.toString());
  }