private static void unregisterKeyOnly(Object key) {
    Region r = cache.getRegion(SEPARATOR + REGION_NAME);
    assertNotNull(r);
    r.unregisterInterest(key);
  }
exercises the ClientSession interface to register interest in a server on behalf of a client

@param clientId the DM of the client
@param key the key that the client is interested in
geode-core/src/distributedTest/java/org/apache/geode/internal/cache/tier/sockets/InterestListDUnitTest.java