[Scripting Question] Looking for an item with an event modifier

[Telemetius]

Hi forum, so I have a question, how can I code an event modifier that checks if the first pkm of my opponent has a specific item?

I know about ".setItem" but what i need is just to check if the pkm already has that item.
Here's what I tried to do:

Events.onTrainerPartyLoad+=proc {|sender,e|
  if e[0] # Trainer data should exist to be loaded, but may not exist somehow
    trainer=e[0][0] # A PokeBattle_Trainer object of the loaded trainer
    items=e[0][1]   # An array of the trainer's items they can use
    party=e[0][2]   # An array of the trainer's Pokémon
    if party[0].isConst?(@item,PBItems,:TESTITEM)
     party[0].form=1
    end
  end
}

Any help?