code: def test_contextualbanditlabel_one_label():
      df = pd.DataFrame({"a": [1], "c": [-0.5], "p": [0.1], "x": [1]})
      conv = DFtoVW(
          df=df,
          label=ContextualbanditLabel("a", "c", "p"),
          features=Feature("x"),
      )
      first_line = conv.convert_df()[0]
      assert first_line == "1:-0.5:0.1 | x:1"
  
imports: import pytest
  import pandas
  from vowpalwabbit.dftovw import ContextualbanditLabel, DFtoVW, Feature, MulticlassLabel, MultiLabel, Namespace, SimpleLabel
label_desc: Use image node_id 28 for calling a global function with example usage: test_contextualbanditlabel_one_label() without return types