code: def test_multiclasslabel_negative_weight_error():
      df = pd.DataFrame({"y": [1], "w": [-0.5], "x": [2]})
      with pytest.raises(ValueError) as value_error:
          DFtoVW(
              df=df,
              label=MulticlassLabel(label="y", weight="w"),
              features=Feature("x"),
          )
      expected = "In argument 'weight' of 'MulticlassLabel', column 'w' must be >= 0."
      assert expected == str(value_error.value)
  
imports: import pytest
  import pandas
  from vowpalwabbit.dftovw import ContextualbanditLabel, DFtoVW, Feature, MulticlassLabel, MultiLabel, Namespace, SimpleLabel
label_desc: Use image node_id 23 for calling a global function with example usage: test_multiclasslabel_negative_weight_error() without return types