wp_add_id3_tag_data() unit test coverage

[rollybueno]

Separating the discussions from https://core.trac.wordpress.org/ticket/63529,
wp_add_id3_tag_data() does not have a test unit coverage which would be great to have as per https://core.trac.wordpress.org/ticket/63529#comment:13

The test unit can go be inside tests/phpunit/tests/media

[ankitkumarshah]

Hi @rollybueno,
Thank you for separating the issue — I’d be glad to help by working on the unit tests for it!
https://core.trac.wordpress.org/ticket/63529#comment:19

[SirLouen]

@rollybueno
Why have you separated this?
It's better to ship patches with their respective unit tests all in one because this could end lost in oblivion, while a needs-unit-test in the original report can serve as a blocker to avoid this happening.
Can we move the work back to #63529?