WroManager implements WroConfigurationChangeListener { public final void registerCallback(final ObjectFactory<LifecycleCallback> callbackFactory) { notNull(callbackFactory); getCallbackRegistry().registerCallback(callbackFactory); } private  WroManager(final Builder builder); final void process(); final String encodeVersionIntoGroupPath(final String groupName, final ResourceType resourceType,
      final boolean minimize); @Override final void onCachePeriodChanged(final long period); @Override final void onModelPeriodChanged(final long period); final void destroy(); final HashStrategy getHashStrategy(); final WroModelFactory getModelFactory(); final ProcessorsFactory getProcessorsFactory(); final CacheStrategy<CacheKey, CacheValue> getCacheStrategy(); final UriLocatorFactory getUriLocatorFactory(); final NamingStrategy getNamingStrategy(); final GroupExtractor getGroupExtractor(); CacheKeyFactory getCacheKeyFactory(); MetaDataFactory getMetaDataFactory(); ResourceWatcher getResourceWatcher(); final void registerCallback(final ObjectFactory<LifecycleCallback> callbackFactory); LifecycleCallbackRegistry getCallbackRegistry(); ResourceAuthorizationManager getResourceAuthorizationManager();  }
@Test(expected = NullPointerException.class) public void cannotRegisterNullCallback() { final WroManager manager = new BaseWroManagerFactory().create(); manager.registerCallback(null); }