code: def test_index_trigger(self):
      slider = SelectionSlider(options=["a", "b", "c"])
      observations = []
  
      def f(change):
          observations.append(change.new)
  
      slider.observe(f, "index")
      assert slider.index == 0
      slider.options = [4, 5, 6]
      assert slider.index == 0
      assert slider.value == 4
      assert slider.label == "4"
      assert observations == [0]
  
file_path: catboost/contrib/python/ipywidgets/py2/ipywidgets/widgets/tests/test_widget_selection.py
imports: import inspect
  import warnings
  from unittest import TestCase
  from traitlets import TraitError
  from ipywidgets import Dropdown, SelectionSlider, Select
label_desc: Use image node_id 2 for calling the TestSelectionSlider obj's underlying member method code with example usage: obj.test_index_trigger() without return types