code: def test_NonUniformImage_scale_monotonicity():
      x = [1.0, 0.0, 10.0]
      y = [1.0, 2.0, 4.0]
      X, Y = np.meshgrid(x, y, indexing="ij")
      Z = X * Y
  
      for args in [(x, y, Z), (y, x, Z)]:
          with pytest.raises(Exception) as ex:
              NonUniformImage(*args)
          assert (
              "The values in x and y must be monotonically increasing."
              in str(ex)
          )
  
file_path: pyqtgraph/tests/graphicsItems/test_NonUniformImage.py
imports: import numpy
  import pytest
  import pyqtgraph
  import pyqtgraph.functions
  from pyqtgraph.colormap import ColorMap
  from pyqtgraph.graphicsItems.NonUniformImage import NonUniformImage
  from pyqtgraph.Qt import QtTest
  from tests.image_testing import assertImageApproved
label_desc: Use image node_id 2 for calling a global function with example usage: test_NonUniformImage_scale_monotonicity() without return types