code: def test_file_schema(app, client):
      @app.get("/image")
      @app.output(
          FileSchema(type="string", format="binary"),
          content_type="image/png",
          description="An image file",
      )
      def get_image():
          return "file"
  
      rv = client.get("/openapi.json")
      assert rv.status_code == 200
      content = rv.json["paths"]["/image"]["get"]["responses"]["200"][
          "content"
      ]
      assert "image/png" in content
      assert content["image/png"]["schema"] == {
          "type": "string",
          "format": "binary",
      }
  
imports: import pytest
  from openapi_spec_validator import validate_spec
  from apiflask.schemas import EmptySchema
  from apiflask.schemas import FileSchema
label_desc: Use image node_id 1 for calling a global function with example usage: test_file_schema(app, client) and returns: str