code: def test_darken():
      """Test darken color function"""
      assert darken("#800", 20) == "#200"
      assert darken("#800e", 20) == "#200e"
      assert darken("#800", 0) == "#800"
      assert darken("#ffffff", 10) == "#e6e6e6"
      assert darken("#000000", 10) == "#000000"
      assert darken("#f3148a", 25) == "#810747"
      assert darken("#f3148aab", 25) == "#810747ab"
      assert darken("#121212", 1) == "#0f0f0f"
      assert darken("#999999", 100) == "#000000"
      assert darken("#99999999", 100) == "#00000099"
      assert darken("#1479ac", 8) == "#105f87"
      assert darken("rgb(136, 0, 0)", 20) == "rgb(34, 0, 0)"
      assert (
          darken("rgba(20, 121, 172, .13)", 8)
          == "rgba(16, 95, 135, 0.13)"
      )
  
imports: from __future__ import division
  from pygal.colors import darken, desaturate, hsl_to_rgb, lighten, parse_color, rgb_to_hsl, rotate, saturate, unparse_color
label_desc: Use image node_id 3 for calling a global function with example usage: test_darken() without return types