protected SerializableRunnableIF waitForSenderRunnable() {
    return () -> WANTestBase.waitForSenderRunningState("ln");
  }
When gateway senders starts to unqueue, stop gateway sender, and check that some evnts are
dispatched to receiving side,
but events are not removed on sending side.
geode-wan/src/distributedTest/java/org/apache/geode/internal/cache/wan/parallel/ParallelWANPersistenceEnabledGatewaySenderCheckPossibleDuplicateDUnitTest.java