code: def test_custom_headers(custom_pages_client):
      response = custom_pages_client.get("/headers")
      assert response.status == 200
      assert response.headers["x-this-is-foo"] == "foo"
      assert response.headers["x-this-is-bar"] == "bar"
      assert response.text == "FOOBAR"
  
file_path: datasette/tests/test_custom_pages.py
imports: import pathlib
  import pytest
  from .fixtures import make_app_client
label_desc: Use image node_id 8 for calling a global function with example usage: test_custom_headers(custom_pages_client) without return types