@Test
  public void testIsEmpty() {
    CustomEntryConcurrentHashMap empty = new CustomEntryConcurrentHashMap();
    CustomEntryConcurrentHashMap map = map5();
    assertTrue(empty.isEmpty());
    assertFalse(map.isEmpty());
  }
isEmpty is true of empty map and false for non-empty
geode-core/src/integrationTest/java/org/apache/geode/internal/util/concurrent/cm/ConcurrentHashMapJUnitTest.java