Honestly? Gift or test, who cares? Either way, you're going to take it with you, if it's a test and she's still hanging around, you'll return it to her, and if it's a gift, then you may as well keep it. Something like this will be tremendously helpful for you in the future after all, the ability to effectively become invisible even to those with senses as sharp as Arcueid or Lugh... though to be fair on those two, Ciel was a fair distance from the two of them already by the time they searched for her so it's not like you'd actually be able to sneak up on either of them with the shroud. Same goes against somebody like Mordred, who should be able to prevent any and all sneak attacks from working against her thanks to her Instinct warning her of any attacks.

Part 18