code: def test_get_prev_widget_value_nonexistent(self):
      session_state = SessionState()
      self.assertRaises(
          KeyError, lambda: session_state["fake_widget_id"]
      )
  
imports: import inspect
  import unittest
  from unittest.mock import ANY, MagicMock, call, patch
  from parameterized import parameterized
  import streamlit
  from streamlit import errors
  from streamlit.proto.Common_pb2 import StringTriggerValue
  from streamlit.proto.WidgetStates_pb2 import WidgetStates
  from streamlit.runtime.scriptrunner.script_run_context import get_script_run_ctx
  from streamlit.runtime.state import coalesce_widget_states
  from streamlit.runtime.state.common import GENERATED_WIDGET_ID_PREFIX, compute_widget_id
  from streamlit.runtime.state.session_state import SessionState, WidgetMetadata
  from streamlit.runtime.state.widgets import user_key_from_widget_id
  from tests.delta_generator_test_case import DeltaGeneratorTestCase
label_desc: Use image node_id 3 for calling the WidgetManagerTests obj's underlying member method code with example usage: obj.test_get_prev_widget_value_nonexistent() without return types