Art Cashin says the Dow is facing a big test and is in trouble if can't hold this level

Art Cashin
Adam Jeffery | CNBC

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UBS floor director Art Cashin said Friday that the dip in markets this week had the potential to be a longer-term sell-off. 

"I think we're in a testing period here. The bulls are clearly on the defensive," Cashin said on "Squawk Alley."