code: def test_label_to_array_raises_error():
      # Pandas DataFrame should have only one column
      y = pd.DataFrame({"a": [0, 1], "b": [2, 3]})
      with pytest.raises(ValueError):
          validation.labels_to_array(y)
  
imports: from cleanlab.internal import validation
  import numpy
  import pandas
  import pytest
label_desc: Use image node_id 3 for calling a global function with example usage: test_label_to_array_raises_error() without return types