@Override
      public Object call() throws Exception {
        final Region r = getCache().getRegion(regionName);
        assertNull(r.putIfAbsent("key0", "value"));
        assertTrue(r.containsKeyOnServer("key0"));
        Object v = r.get("key0");
        assertNull("expected null but was " + v, v);
        return null;
      }
tests for the concurrentMapOperations. there are more tests in ClientServerMiscDUnitTest
geode-core/src/distributedTest/java/org/apache/geode/internal/cache/ConcurrentMapOpsDUnitTest.java