I don't know if TestAmenT really followed Metallica on The Ritual. I'd rather say it was the opposite way. TestAmenT was first to release melodic albums (Practice, Souls) and Metallica simply put it to a next level (losing most of the metallic sound, unlike TestAmenT)- of course only if metallica ever heard testament, because if they don't know this band, they cannot be accused of following them and probably just had similar ideas, only some time later.
Black album is obviousely more melodic and softer than these two, but some similarities cannot be denied (so I don't really find metallica's self-titled album that innovative and groundbreaking).
As for The Ritual, I'd say it was a logical step forward for TestAmenT after Souls- it had nothing to do with copying anyone's ideas- they were going further on the path they had paved a couple of years before Metallica decided to change musically (or sell out). That's how I see it.