code: def test_update_model_cost():
      try:
          litellm.register_model(
              {
                  "gpt-4": {
                      "max_tokens": 8192,
                      "input_cost_per_token": 0.00002,
                      "output_cost_per_token": 0.00006,
                      "litellm_provider": "openai",
                      "mode": "chat",
                  },
              }
          )
          assert (
              litellm.model_cost["gpt-4"]["input_cost_per_token"]
              == 0.00002
          )
      except Exception as e:
          pytest.fail(f"An error occurred: {e}")
  
imports: import sys, os
  import traceback
  import pytest
  import litellm
label_desc: Use image node_id 1 for calling a global function with example usage: test_update_model_cost() without return types