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.
