code: def test_non_default_index():
      df = pd.DataFrame({"y": [0], "x": [1]}, index=[1])
      conv = DFtoVW(
          df=df, label=SimpleLabel("y"), features=Feature("x")
      )
      first_line = conv.convert_df()[0]
      assert first_line == "0 | x:1"
  
imports: import pytest
  import pandas
  from vowpalwabbit.dftovw import ContextualbanditLabel, DFtoVW, Feature, MulticlassLabel, MultiLabel, Namespace, SimpleLabel
label_desc: Use image node_id 17 for calling a global function with example usage: test_non_default_index() without return types