### Question:
AliasBlurFilterCache extends BlurFilterCache { @Override public Filter fetchPreFilter(String table, String filterStr) { FilterKey filterKey = new FilterKey(table, filterStr); return _preFilterCacheMap.get(filterKey); } AliasBlurFilterCache(BlurConfiguration configuration); @Override Filter storePreFilter(String table, String filterStr, Filter filter, FilterParser filterParser); @Override Filter storePostFilter(String table, String filterStr, Filter filter, FilterParser filterParser); @Override Filter fetchPreFilter(String table, String filterStr); @Override Filter fetchPostFilter(String table, String filterStr); @Override void closing(String table, String shard, BlurIndex index); @Override void opening(String table, String shard, BlurIndex index);  }### Answer:
@Test public void testFetchPreFilterEmpty() throws IOException { BlurConfiguration configuration = new BlurConfiguration(); AliasBlurFilterCache defaultBlurFilterCache = new AliasBlurFilterCache(configuration); Filter fetchPreFilter = defaultBlurFilterCache.fetchPreFilter(TABLE, TEST_FILTER); assertNull(fetchPreFilter); }