Write a class to keep track of a balance in a bank account with a varying annual interest rate. The constructor will set both the balance and the annual interest rate to some initial values (with defaults of zero). The class should have member functions to change or retrieve the current balance or interest rate. There should also be functions to make a deposit (add to the balance) or a withdrawal (subtract from the balance). Finally, there should be a function that adds interest to the balance at the current interest rate. This function should have a parameter indicating how many years worth of interest are to be added (for example, 0.5 years indicates that the account should have six months interest added). Do not construct an interactive program. Instead, create a test program using assertions. The test program needs to check all the functionality of each class using assertions.