code: def test_monotonicity():
      """Test for monotonicity operator"""
      tensor = T.tensor(np.random.rand(20, 10))
      # Monotone increasing
      tensor_monoton = monotonicity_prox(tensor)
      assert_(np.all(np.diff(tensor_monoton, axis=0) >= 0))
      # Monotone decreasing
      tensor_monoton = monotonicity_prox(tensor, decreasing=True)
      assert_(np.all(np.diff(tensor_monoton, axis=0) <= 0))
  
imports: import numpy
  from ...None import backend
  from ..proximal import svd_thresholding, smoothness_prox, soft_thresholding, hals_nnls, fista, active_set_nnls, procrustes, hard_thresholding, soft_sparsity_prox, simplex_prox, normalized_sparsity_prox, monotonicity_prox, unimodality_prox, l2_prox, l2_square_prox, admm
  from ...testing import assert_, assert_array_equal, assert_array_almost_equal
  from tensorly import tensor_to_vec, truncated_svd
  import pytest
label_desc: Use image node_id 6 for calling a global function with example usage: test_monotonicity() without return types