code: def test_mixed_type_features():
      df = pd.DataFrame({"y": [1], "x1": ["a"], "x2": [2]})
      conv = DFtoVW(
          label=SimpleLabel("y"),
          features=[Feature(value=colname) for colname in ["x1", "x2"]],
          df=df,
      )
      first_line = conv.convert_df()[0]
      assert first_line == "1 | x1=a x2:2"
  
imports: import pytest
  import pandas
  from vowpalwabbit.dftovw import ContextualbanditLabel, DFtoVW, Feature, MulticlassLabel, MultiLabel, Namespace, SimpleLabel
label_desc: Use image node_id 9 for calling a global function with example usage: test_mixed_type_features() without return types