code: def test_gantt_validate_colors(self):
      # validate the gantt colors variable
  
      df = [
          {
              "Task": "Job A",
              "Start": "2009-02-01",
              "Finish": "2009-08-30",
              "Complete": 75,
              "Resource": "A",
          },
          {
              "Task": "Job B",
              "Start": "2009-02-01",
              "Finish": "2009-08-30",
              "Complete": 50,
              "Resource": "B",
          },
      ]
  
      pattern = (
          "Whoops! The elements in your rgb colors tuples cannot "
          "exceed 255.0."
      )
  
      self.assertRaisesRegex(
          PlotlyError,
          pattern,
          ff.create_gantt,
          df,
          index_col="Complete",
          colors="rgb(300,1,1)",
      )
  
      self.assertRaises(
          PlotlyError,
          ff.create_gantt,
          df,
          index_col="Complete",
          colors="foo",
      )
  
      pattern2 = (
          "Whoops! The elements in your colors tuples cannot "
          "exceed 1.0."
      )
  
      self.assertRaisesRegex(
          PlotlyError,
          pattern2,
          ff.create_gantt,
          df,
          index_col="Complete",
          colors=(2, 1, 1),
      )
  
      # verify that if colors is a dictionary, its keys span all the
      # values in the index column
      colors_dict = {75: "rgb(1, 2, 3)"}
  
      pattern3 = (
          "If you are using colors as a dictionary, all of its "
          "keys must be all the values in the index column."
      )
  
      self.assertRaisesRegex(
          PlotlyError,
          pattern3,
          ff.create_gantt,
          df,
          index_col="Complete",
          colors=colors_dict,
      )
  
      # check: index is set if colors is a dictionary
      colors_dict_good = {50: "rgb(1, 2, 3)", 75: "rgb(5, 10, 15)"}
  
      pattern4 = (
          "Error. You have set colors to a dictionary but have not "
          "picked an index. An index is required if you are "
          "assigning colors to particular values in a dictionary."
      )
  
      self.assertRaisesRegex(
          PlotlyError,
          pattern4,
          ff.create_gantt,
          df,
          colors=colors_dict_good,
      )
  
      # check: number of colors is equal to or greater than number of
      # unique index string values
      pattern5 = (
          "Error. The number of colors in 'colors' must be no less "
          "than the number of unique index values in your group "
          "column."
      )
  
      self.assertRaisesRegex(
          PlotlyError,
          pattern5,
          ff.create_gantt,
          df,
          index_col="Resource",
          colors=["#ffffff"],
      )
  
      # check: if index is numeric, colors has at least 2 colors in it
      pattern6 = (
          "You must use at least 2 colors in 'colors' if you "
          "are using a colorscale. However only the first two "
          "colors given will be used for the lower and upper "
          "bounds on the colormap."
      )
  
      self.assertRaisesRegex(
          PlotlyError,
          pattern6,
          ff.create_gantt,
          df,
          index_col="Complete",
          colors=["#ffffff"],
      )
  
imports: import math
  from unittest import TestCase
  import datetime
  import plotly.figure_factory
  import plotly.io
  from plotly.exceptions import PlotlyError
  from plotly.tests.test_optional.optional_utils import NumpyTestUtilsMixin
  from plotly.graph_objs import graph_objs
  from plotly.tests.utils import TestCaseNoTemplate
label_desc: Use image node_id 3 for calling the TestGantt obj's underlying member method code with example usage: obj.test_gantt_validate_colors() without return types