Ask them to explain how a smoke test is going to help - because I doubt that it will. But if you report the specific code people could say more. If it is P0453, as Caddyman suggests, then the first thing to check is the sensor’s wiring.
IF, in fact, there is an actual evap system problem, it will be a system blockage - not a leak. In a smoke test you just pump smoke into the lines and look for where it escapes. If there’s a blockage, there will be no escape.
What kind of a shop did you bring it to.