Youtube-dl's counter claim states that though those lines of code did not violate the DMCA, they have replaced them with videos without copyright music.
That sounds like they didn't really have any reason to make major label music videos part of the tests, it was just a developers personal preference. Though, it doesn't prove this is the case.
That commit details the replacement of the music videos with a generic test video, exactly what I said. I'm unsure how it is supposed to show it is not the case.
Incorrect. There's a single green line that has an alteration to replace a music video ID "UxxajLWwzqY" in a test case that actually only makes use of ID "BaW_jenozKc" ("Use the first video ID in the URL").
The removed "Test generic use_cipher_signature video (#897)" case did make use of ID UxxajLWwzqY.
I see what you mean, but the extractor file still features how to deal with videos containing the cipher, all that was removed was the tests. Testing the generic cipher video may have been ruled unnecessary as it's universal.
That's the partial win here - repo restored with tests referencing the RIAA related videos removed but the code dealing with the rolling cipher itself still intact.
And next time youtube makes one of their frequent changes to their website the extractor will break in some way. Somebody will work to fix it and make use of the same tests, only now some of them won't be in the public codebase.
