code: def test_as_type_in_features():
      df = pd.DataFrame({"y": [1], "a": [2], "b": [3], "c": ["4"]})
      features = [
          Feature("a", as_type="categorical"),
          Feature("b"),
          Feature("c", as_type="numerical"),
      ]
      conv = DFtoVW(label=SimpleLabel("y"), features=features, df=df)
      first_line = conv.convert_df()[0]
      assert first_line == "1 | a=2 b:3 c:4"
  
imports: import pytest
  import pandas
  from vowpalwabbit.dftovw import ContextualbanditLabel, DFtoVW, Feature, MulticlassLabel, MultiLabel, Namespace, SimpleLabel
label_desc: Use image node_id 10 for calling a global function with example usage: test_as_type_in_features() without return types