@Test
  public void unregisterClientMissingClientIsDoesNotIncrementStat() {
    ClientProxyMembershipID mockId = mock(ClientProxyMembershipID.class);
    clientHealthMonitor.registerClient(mockId);

    clientHealthMonitor.unregisterClient(mockId, null, true, null);
    clientHealthMonitor.unregisterClient(mockId, null, true, null);
    assertThat(clientHealthMonitor.getClientHeartbeats()).doesNotContainKey(mockId);

    // incremented 1 time for the initial unregisterClient.
    verify(mockStats).incClientUnRegisterRequests();
  }
This is a functional-test for <code>ClientHealthMonitor</code>.
geode-core/src/test/java/org/apache/geode/internal/cache/tier/sockets/ClientHealthMonitorTest.java