@Override
  protected void after() throws Throwable {
    invoker().invokeInEveryVMAndController(this::invokeAfter);
  }
DistributedBlackboard provides mailboxes and synchronization gateways for distributed tests.

<p>
Tests may use the blackboard to pass objects and status between JVMs with mailboxes instead of
using static variables in classes. The caveat being that the objects will be serialized using
Java serialization.

<p>
Gates may be used to synchronize operations between distributed test JVMs. Combined with
Awaitility these can be used to test for conditions being met, actions having happened, etc.

<p>
Look for references to the given methods in your IDE for examples.
geode-dunit/src/main/java/org/apache/geode/test/dunit/rules/DistributedBlackboard.java