@Test(expected = QuorumException.class)
 public void testPutIfAbsentOperationThrowsExceptionWhenQuorumSizeNotMet() {
   cache4.putIfAbsent(1, "");
 }
 @Test
 public void testPutIfAbsentOperationSuccessfulWhenQuorumSizeMet() {
   cache1.putIfAbsent(1, "");
 }