code: def test_to_vw_file(model, df):
      expected = [
          "1 0|user 1 |item 8",
          "5 1|user 3 |item 7",
          "3 2|user 2 |item 7",
      ]
      model.to_vw_file(df, train=True)
      with open(model.train_file, "r") as f:
          assert f.read().splitlines() == expected
      del model
  
file_path: recommenders/tests/unit/recommenders/models/test_vowpal_wabbit.py
imports: import os
  import pytest
  from unittest import mock
  import pandas
  from recommenders.models.vowpal_wabbit.vw import VW
label_desc: Use image node_id 7 for calling a global function with example usage: test_to_vw_file(model, df) without return types