code: def test_multiple_lines():
      df = pd.DataFrame({"y": [1, -1], "x": [1, 2]})
      conv = DFtoVW(
          label=SimpleLabel("y"), features=Feature(value="x"), df=df
      )
      lines_list = conv.convert_df()
      assert lines_list == ["1 | x:1", "-1 | x:2"]
  
imports: import pytest
  import pandas
  from vowpalwabbit.dftovw import ContextualbanditLabel, DFtoVW, Feature, MulticlassLabel, MultiLabel, Namespace, SimpleLabel
label_desc: Use image node_id 8 for calling a global function with example usage: test_multiple_lines() without return types