@pytest.mark.vcr(before_record_response=...) behaves differently when recording and playing back

[akaihola]

Describe the bug
If I use a before_record_response= callback which modifies the response, the original response is used when the response is being recorded, and the modified response when it's being played back.

To Reproduce
Steps to reproduce the behavior:

1. On this test file test_modified_response.py:

   import pytest
   import requests
   
   def modify_response(response):
       response["body"]["string"] = b"Modified response"
       return response
   
   @pytest.mark.vcr(before_record_response=[modify_response])
   def test_modified_response():
       response = requests.get(
           "https://github.com/kiwicom/pytest-recording",
           headers={"Accept-Encoding": "identity"},  # prevent compression
       )
       assert response.content == b"Modified response"

2. Run this command:

   pytest --record-mode=once test_modified_response.py

3. Observe that the test fails, while the recorded cassette .yaml file has the modified content:

     response:
       body:
         string: Modified response

4. Run this command:

   pytest test_modified_response.py

5. Observe that the test passes

Expected behavior
For the example above, both test runs should pass.

More generally, the modified response should be returned to the calling HTTP client also when it's being recorded.

Environment (please complete the following information):

• OS: Linux (NixOS 22.11)
• Python version: 3.11.2
• pytest-recording version: 0.12.2
• pytest version: 7.2.2

[akaihola]

This is actually probably better fixed on the VCRpy side – see kevin1024/vcrpy#544.