code: def test_cp_to_vec():
      """Test for cp_to_vec"""
      U1 = np.reshape(np.arange(1, 10, dtype=float), (3, 3))
      U2 = np.reshape(np.arange(10, 22, dtype=float), (4, 3))
      U3 = np.reshape(np.arange(22, 28, dtype=float), (2, 3))
      U4 = np.reshape(np.arange(28, 34, dtype=float), (2, 3))
      U = [tl.tensor(t) for t in [U1, U2, U3, U4]]
      cp_tensor = CPTensor((tl.ones(3), U))
      full_tensor = cp_to_tensor(cp_tensor)
      true_res = tensor_to_vec(full_tensor)
      res = cp_to_vec(cp_tensor)
      assert_array_equal(
          true_res,
          res,
          err_msg="khatri_rao product converted incorrectly to vec.",
      )
  
imports: import numpy
  import tensorly
  from ..tenalg import khatri_rao, mode_dot
  from ..cp_tensor import cp_to_tensor, cp_to_unfolded, cp_to_vec, _validate_cp_tensor, cp_normalize, CPTensor, cp_mode_dot, cp_norm, cp_flip_sign, _cp_n_param, validate_cp_rank, cp_lstsq_grad, cp_permute_factors
  from ..base import unfold, tensor_to_vec
  from tensorly.random import random_cp
  from tensorly.testing import assert_equal, assert_raises, assert_, assert_array_equal, assert_array_almost_equal
  import pytest
label_desc: Use image node_id 7 for calling a global function with example usage: test_cp_to_vec() without return types