Curious to know if it was not possible for YouTube-dl to create content which was ‘similar’ to the infringing ones & upload it on YouTube for their test cases?

AFAIK the features they're testing are only available to specific partners. I can't be sure, but it isn't obvious how they could go about doing this.

Or they could have had the YouTube links in another file, not part of the repo, and only download and parse it when tests are run.

Best thing would be for them to just upload their own test videos with the various formats and test against those.

Most of this comment chain has been about why they couldn't do that. They were testing against special features that are only available to select partners.

One solution would be to load those links from environment variables, similar to how it's done with API access keys and other sensitive data. This would mildly inconvenience the devs by having to copy the links to those types of content by hand and set the vars before running the tests, but none of the "infringing" links would be present in the repo itself.

Hi Nullc, long time no see! :-) And shoot, that is annoying.

It makes for really bad optics though. Gforz's suggestion to upload test video with similar parameters is -in 20/20 hindsight- probably the better plan. Definitely better than giving bad ideas to copyright lawyers.