bankaccounts

src/main/java/rocks/zipcode/quiz5/objectorientation/account/BankAccount.java

 
 
     public void deposit(Double amountToIncreaseBy) {
-        balance += amountToIncreaseBy;
+        if(amountToIncreaseBy >= 0) {
+            balance += amountToIncreaseBy;
+        } else {
+            throw new IllegalArgumentException();
+        }
     }
 
     public void withdrawal(Double amountToDecreaseBy) {