Unit tests for `_post_process_results`

[AetherUnbound]

Description

Add unit tests for the _post_process_results function:

https://github.com/WordPress/openverse-api/blob/v2.5.10/api/catalog/api/controllers/search_controller.py#L107

Additional context

Part of a series of unit test issues (see #871 & #872)

Implementation

• [ ] 🙋 I would be interested in implementing this feature.

[sourav25998]

Hello @dhruvkb . Can you please assign this issue to me

[dhruvkb]

Sure @sourav25998, assigning the issue to you. If you need help, feel free to comment here or send a message to the #openverse channel in the Making WordPress Slack workspace.