code: def test_flatten_unflatten():
      """Unit tests for the flatten and unflatten methods."""
      H = 2.0 * qml.PauliX(0) @ qml.PauliY(1) + 3.0 * qml.PauliY(
          0
      ) @ qml.PauliZ(1)
      time = 0.5
      frequencies = (2, 4)
      shifts = (1, 0.5)
      op = qml.CommutingEvolution(
          H, time, frequencies=frequencies, shifts=shifts
      )
      data, metadata = op._flatten()
  
      assert hash(metadata)
  
      assert len(data) == 2
      assert data[1] is H
      assert data[0] == time
      assert metadata == (frequencies, shifts)
  
      new_op = type(op)._unflatten(*op._flatten())
      assert qml.equal(op, new_op)
      assert op is not new_op
  
file_path: pennylane/tests/templates/test_subroutines/test_commuting_evolution.py
imports: import pytest
  from scipy.linalg import expm
  import pennylane
  from pennylane import numpy
label_desc: Use image node_id 2 for calling a global function with example usage: test_flatten_unflatten() without return types