In a package named "execution", implement the following classes: • class Valuable • • Constructor takes one variable as a parameter named "item" of type Valuable (use var) • This class represents someone with a valuable item they are wiling to trade. Each trader can only own 1 item at a time which is stored in the "item" state variable • class TradeAgreement • Constructor takes 2 objects of type Trader • One method named "executeTrade" that take no parameters and returns Unit • When this method is called, swap the items belonging to the 2 traders from the constructor (ie. When a TradeAgreement is created, 2 people are agreeing to a trade. When executeTrade is called, they physically trade those items) • The agreement can only be executed once. If this method is called more than once for a single agreement, additional trades are not made (ie. The people do not trade back to their original items if this method is called twice)

Testing: In a package named "tests" create a Scala class named "TestTrading" as a test suite that tests all the functionality listed above