code: def test_add_lag_features(snarimax, Y, errors, expected):
      features = snarimax._add_lag_features(x=None, Y=Y, errors=errors)
      assert features == expected
  
file_path: river/river/time_series/test_snarimax.py
imports: from __future__ import annotations
  import calendar
  import math
  import random
  import pytest
  import sympy
  from river import compose, datasets, metrics, time_series
  from river.time_series.snarimax import Differencer
label_desc: Use image node_id 4 for calling a global function with example usage: test_add_lag_features(snarimax, Y, errors, expected) without return types