code: def test_validate_gantt(self):
      # validate the basic gantt inputs
  
      df = [
          {
              "Task": "Job A",
              "Start": "2009-02-01",
              "Finish": "2009-08-30",
              "Complete": "a",
          }
      ]
  
      pattern2 = (
          "In order to use an indexing column and assign colors to "
          "the values of the index, you must choose an actual "
          "column name in the dataframe or key if a list of "
          "dictionaries is being used."
      )
  
      self.assertRaisesRegex(
          PlotlyError, pattern2, ff.create_gantt, df, index_col="foo"
      )
  
      df = "foo"
  
      pattern3 = (
          "You must input either a dataframe or a list of "
          "dictionaries."
      )
  
      self.assertRaisesRegex(PlotlyError, pattern3, ff.create_gantt, df)
  
      df = []
  
      pattern4 = (
          "Your list is empty. It must contain at least one "
          "dictionary."
      )
  
      self.assertRaisesRegex(PlotlyError, pattern4, ff.create_gantt, df)
  
      df = ["foo"]
  
      pattern5 = "Your list must only include dictionaries."
  
      self.assertRaisesRegex(PlotlyError, pattern5, ff.create_gantt, df)
  
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 1 for calling the TestGantt obj's underlying member method code with example usage: obj.test_validate_gantt() without return types