docstr: Test that ops with a period of 2 raised to an even power are empty lists.
docstr_tok: ["Test","that","ops","with","a","period","of","2","raised","to","an","even","power","are","empty","lists","."]
code: def test_period_two_pow_even(self, op, n):
      """Test that ops with a period of 2 raised to an even power are empty lists."""
      assert len(op.pow(n)) == 0
  
imports: import copy
  import numpy
  import pytest
  from scipy.linalg import fractional_matrix_power
  from scipy.sparse import csr_matrix
  from scipy.stats import unitary_group
  from gate_data import CY, CZ
  import pennylane
  from pennylane.wires import Wires
  from pennylane.operation import AnyWires
  from pennylane.ops.qubit.matrix_ops import QubitUnitary
label_desc: Use image node_id 2 for calling the TestPowMethod obj's underlying member method code with example usage: obj.test_period_two_pow_even(op, n) without return types