### Question:
PageCacheArrayFactoryMonitor implements NumberArrayFactory.Monitor { public String pageCacheAllocationOrNull() { String failure = failedFactoriesDescription.get(); if ( failure != null ) { failedFactoriesDescription.compareAndSet( failure, null ); } return failure; }  @Override void allocationSuccessful( long memory, NumberArrayFactory successfulFactory,
            Iterable<NumberArrayFactory.AllocationFailure> attemptedAllocationFailures ); String pageCacheAllocationOrNull();  }### Answer:
@Test public void shouldReturnNullFailureOnNoFailure() { assertNull( monitor.pageCacheAllocationOrNull() ); }