MockHelixManager manager = new MockHelixManager();
ResourceMonitor monitor = new ResourceMonitor(_clusterName, _dbName);
HelixDataAccessor helixDataAccessor = manager.getHelixDataAccessor();
Builder keyBuilder = helixDataAccessor.keyBuilder();
ExternalView externalView = helixDataAccessor.getProperty(keyBuilder.externalView(_dbName));
IdealState idealState = helixDataAccessor.getProperty(keyBuilder.idealStates(_dbName));
monitor.updateExternalView(externalView, idealState);
AssertJUnit.assertEquals(monitor.getDifferenceWithIdealStateGauge(), 0);