@Override
    public List<String> getAllDatabaseNames() {
        return get(databaseNamesCache, "");
    }
@Test
    public void testGetAllDatabaseNames() {
        CachingDeltaLakeMetastore cachingDeltaLakeMetastore =
                CachingDeltaLakeMetastore.createCatalogLevelInstance(metastore, executor, expireAfterWriteSec,
                        refreshAfterWriteSec, 100);

        List<String> databaseNames = cachingDeltaLakeMetastore.getAllDatabaseNames();
        Assert.assertEquals(Lists.newArrayList("db1", "db2"), databaseNames);
        CachingDeltaLakeMetastore queryLevelCache = CachingDeltaLakeMetastore.
                createQueryLevelInstance(cachingDeltaLakeMetastore, 100);
        Assert.assertEquals(Lists.newArrayList("db1", "db2"), queryLevelCache.getAllDatabaseNames());
    }