code: def test_json_spec_mimetype(app, client):
      rv = client.get("/openapi.json")
      assert rv.status_code == 200
      assert rv.mimetype == "application/json"
  
      app.config["JSON_SPEC_MIMETYPE"] = "application/custom.json"
  
      rv = client.get("/openapi.json")
      assert rv.status_code == 200
      assert rv.mimetype == "application/custom.json"
  
file_path: apiflask/tests/test_settings_openapi_spec.py
imports: import json
  import pytest
  from apiflask import APIFlask
  from apiflask.commands import spec_command
label_desc: Use image node_id 1 for calling a global function with example usage: test_json_spec_mimetype(app, client) without return types