docstr: Test 'matrices' key pair is not a list.
docstr_tok: ["Test","'matrices","'","key","pair","is","not","a","list","."]
code: def test_cache_matrices_not_list(self, mat, op):
      """Test 'matrices' key pair is not a list."""
      assert op.label(cache={"matrices": 0}) == "U"
  
imports: import pytest
  import numpy
  from scipy.stats import unitary_group
  from gate_data import TSWAP
  import pennylane
  from pennylane.wires import Wires
  from pennylane.operation import DecompositionUndefinedError
label_desc: Use image node_id 3 for calling the TestUnitaryLabels obj's underlying member method code with example usage: obj.test_cache_matrices_not_list(mat, op) without return types