1. Use TDD to code two classes that interact with each other.

We're going to build a BankAccount class where one instance of the class can transfer money to another instance through a Transfer class. The Transfer class acts as a space for a transaction between two instances of the bank account class. Think of it this way: you can't just transfer money to another account without the bank running checks first. Transfer instances will do all of this, as well as check the validity of the accounts before the transaction occurs. Transfer instances should be able to reject a transfer if the accounts aren't valid or if the sender doesn't have the money.

Transfers start out in a "pending" status. They can be executed and go to a "complete" state. They can also go to a "rejected" status. A completed transfer can also be reversed and go into a "reversed" status.

Pass the tests. They are deliberatively vague; your design is up to you! Read the test output and test files very carefully to get through this one.

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