### Question:
GraphStoreCatalog { public static int graphStoresCount() { return userCatalogs .values() .stream() .mapToInt(userCatalog -> userCatalog.getGraphStores().values().size()) .sum(); } private  GraphStoreCatalog(); static GraphStoreWithConfig get(String username, NamedDatabaseId databaseId, String graphName); static void set(GraphCreateConfig config, GraphStore graphStore); static Optional<Graph> getUnion(String username, NamedDatabaseId databaseId, String graphName); static boolean exists(String username, NamedDatabaseId databaseId, String graphName); static void remove(
        String username,
        NamedDatabaseId databaseId,
        String graphName,
        Consumer<GraphStoreWithConfig> removedGraphConsumer,
        boolean failOnMissing
    ); static int graphStoresCount(); static int graphStoresCount(NamedDatabaseId databaseId); static Optional<Map<String, Object>> getDegreeDistribution(String username, NamedDatabaseId databaseId, String graphName); static void setDegreeDistribution(String username, NamedDatabaseId databaseId, String graphName, Map<String, Object> degreeDistribution); static void removeAllLoadedGraphs(); static Map<GraphCreateConfig, GraphStore> getGraphStores(String username); static Map<GraphCreateConfig, GraphStore> getGraphStores(String username, NamedDatabaseId databaseId);  }### Answer:
@Test void graphStoresCount() { assertEquals(0, GraphStoreCatalog.graphStoresCount(DATABASE_ID)); GraphStoreCatalog.set(CONFIG, graphStore); assertEquals(1, GraphStoreCatalog.graphStoresCount(DATABASE_ID)); GraphStoreCatalog.remove(USER_NAME, DATABASE_ID, GRAPH_NAME, graphStoreWithConfig -> {}, true); assertEquals(0, GraphStoreCatalog.graphStoresCount(DATABASE_ID)); }