### Question:
ModelCatalog { public static Collection<Model<?, ?>> list(String username) { return getUserCatalog(username).list(); } private  ModelCatalog(); static void set(Model<?, ?> model); static Model<D, C> get(
        String username, String modelName, Class<D> dataClass, Class<C> configClass
    ); static boolean exists(String username, String modelName); static Optional<String> type(String username, String modelName); static Model<?, ?> drop(String username, String modelName); static Collection<Model<?, ?>> list(String username); static Model<?, ?> list(String username, String modelName); static void removeAllLoadedModels();  }### Answer:
@Test void shouldReturnEmptyList() { assertEquals(0, ModelCatalog.list(USERNAME).size()); }