code: def test_desaturate():
      """Test color desaturation function"""
      assert desaturate("#000", 20) == "#000"
      assert desaturate("#fff", 20) == "#fff"
      assert desaturate("#8a8", 100) == "#999"
      assert desaturate("#855", 20) == "#726b6b"
  
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 6 for calling a global function with example usage: test_desaturate() without return types