code: def test_source():
      o = src.copy()
      o[0, :2] = clear
      np.testing.assert_equal(source(src, clear), o)
      o[0, :2] = clear_white
      np.testing.assert_equal(source(src, clear_white), o)
      o[0, :2] = half_blue
      np.testing.assert_equal(source(src, half_blue), o)
  
imports: from __future__ import annotations
  import numpy
  from datashader.composite import add, saturate, over, source
label_desc: Use image node_id 1 for calling a global function with example usage: test_source() without return types