private void queueIsDrained() {
    assertThat(unprocessedTokensSize("ln"))
        .as("number of unprocessed tokens in queue")
        .isEqualTo(0);
  }
Test to validate that the maximum number of senders plus one fails to be created.
geode-wan/src/distributedTest/java/org/apache/geode/internal/cache/wan/serial/SerialGatewaySenderQueueDistributedTest.java