[TestMethod] 
 public void TestCase1() 

 {
     
 var mc = new MasterCard(100m); 
 var visa = new Visa(100m); 
 var disc = new Discover(100m); 

 wallet.Cards = new List <Card> {
         mc, visa, disc
     }; 
 person.Wallets = new List <Wallet> {
         wallet
     }; 

 Assert.AreEqual(16, person.CalculateInterest()); 

 Assert.AreEqual(10, visa.CalculateInterest()); 
 Assert.AreEqual(5, mc.CalculateInterest()); 
 Assert.AreEqual(1, disc.CalculateInterest()); 

 }