code: def test_pauli_word_prefactor_raises_error(op):
      """Test that an error is raised when the operator provided is not a valid PauliWord."""
      with pytest.raises(
          ValueError, match="Expected a valid Pauli word, got"
      ):
          pauli_word_prefactor(op)
  
imports: import pytest
  import pennylane
  from pennylane.pauli import pauli_word_prefactor
label_desc: Use image node_id 2 for calling a global function with example usage: test_pauli_word_prefactor_raises_error(op) without return types