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Intamin do pull through tests on their coaster. The train is pictured here slowly being pulled through the circuit and once this is done, they will start testing by running complete trains through (likely with dummies). The arch you noticed is used to test the safety envelope to make sure things like supports and scenery are not too close.
I find it strange that there’s no testing dummy as that should be a priority or maybe not at that moment, but did you see how there’s some arch thing in there? I think that has to do with some effects in the coaster and that is what they're testing.
Did they confirm Manta as the name for the launch coaster or is it just a rumor?