code: def client() -> TestClient:
      config = GatewayConfig(
          **{
              "routes": [
                  {
                      "name": "completions-gpt4",
                      "route_type": "llm/v1/completions",
                      "model": {
                          "name": "gpt-4",
                          "provider": "openai",
                          "config": {
                              "openai_api_key": "mykey",
                              "openai_api_base": "https://api.openai.com/v1",
                              "openai_api_version": "2023-05-10",
                              "openai_api_type": "openai",
                          },
                      },
                  },
                  {
                      "name": "chat-gpt4",
                      "route_type": "llm/v1/chat",
                      "model": {
                          "name": "gpt-4",
                          "provider": "openai",
                          "config": {
                              "openai_api_key": "MY_API_KEY",
                          },
                      },
                  },
              ]
          }
      )
      app = create_app_from_config(config)
      return TestClient(app)
  
file_path: mlflow/tests/gateway/test_gateway_app.py
imports: from unittest import mock
  import pytest
  from fastapi.testclient import TestClient
  from mlflow.exceptions import MlflowException
  from mlflow.gateway.app import create_app_from_config, create_app_from_env
  from mlflow.gateway.config import GatewayConfig
  from mlflow.gateway.constants import MLFLOW_GATEWAY_CRUD_ROUTE_BASE, MLFLOW_GATEWAY_ROUTE_BASE
  from tests.gateway.tools import MockAsyncResponse
label_desc: Use image node_id 1 for calling a global function with example usage: client() and returns: TestClient