private static void unregisterKeyForClient(DistributedMember clientId, Object key) {
    try {
      ClientSession cs = server.getClientSession(clientId);
      if (cs.isPrimary()) {
        cs.unregisterInterest(SEPARATOR + REGION_NAME, key, false);
      }
    } catch (Exception ex) {
      Assert.fail("failed while un-registering key(" + key + ") for client " + clientId, ex);
    }
  }
unregister a key for a particular client in the server

@param clientId the client's ID
@param key the key it's no longer interest in
geode-core/src/distributedTest/java/org/apache/geode/internal/cache/tier/sockets/InterestListDUnitTest.java