Half way

src/main/java/com/zipcoder/payment/Check.java

     public String getAccountNumber() {
     return accountNumber;
     }
+
+    public int compareTo(Payment o) {
+        return 0;
+    }
 }

src/main/java/com/zipcoder/payment/CreditCard.java

     String number;
     int expiredMonth;
     int expiredYear;
+    int compare;
 
     public  CreditCard(){
         id = 12345;
         number = "4551";
         expiredMonth = 10;
         expiredYear = 2019;
+        int compare = 0;
     }
 
     public Long getId() {
     public int getExpiredYear() {
         return expiredYear;
     }
+
+    public int compareTo(Payment o) {
+        if (this.getShortDescription().compareTo(o.getShortDescription()) < 0){
+            compare = -1;
+        }
+        else if (this.getShortDescription().compareTo(o.getShortDescription()) > 0){
+            compare = 1;
+        }
+
+        else{
+            compare = 0;
+        }
+
+        return compare;
+    }
 }

src/main/java/com/zipcoder/payment/PayPal.java

     }
 
     public String getShortDescription() {
-        return null;
+        return ("PayPal" + payerName + email);
     }
 
     public void setId(long id) {
     public String getEmail() {
         return email;
     }
+
+    public int compareTo(Payment o) {
+        return 0;
+    }
 }

src/main/java/com/zipcoder/payment/Payment.java

 package com.zipcoder.payment;
 
-public interface Payment {
+public interface Payment extends Comparable<Payment> {
 
     Long getId();
 

src/test/java/com/zipcoder/payment/CheckTest.java

 
     @Test
     public void getShortDescription() {
+        Check check = new Check();
+        String getShortDescription = ("Check" + check.getPayerName() + check.getAccountNumber());
+        String expectedGetShortDescription = ("Check" + check.getPayerName() + check.getAccountNumber());
+        String actualGetShortDescription = check.getShortDescription();
+        assertEquals(expectedGetShortDescription, actualGetShortDescription);
+    }
+
+
+    @Test
+    public void compareTo1() {
+        CreditCard creditCard = new CreditCard();
+        Check check = new Check();
+        int expectedCompareTo = 1;
+        int actualCompareTo = check.compareTo(creditCard);
+        assertEquals(expectedCompareTo, actualCompareTo);
+    }
 
+    @Test
+    public void compareTo2() {
+        Check check = new Check();
+        PayPal payPal = new PayPal();
+        int expectedCompareTo = -1;
+        int actualCompareTo = check.compareTo(payPal);
+        assertEquals(expectedCompareTo, actualCompareTo);
+    }
+
+    @Test
+    public void compareTo3() {
+        Check check = new Check();
+        int expectedCompareTo = 0;
+        int actualCompareTo = check.compareTo(check);
+        assertEquals(expectedCompareTo, actualCompareTo);
     }
 }

src/test/java/com/zipcoder/payment/CreditCardTest.java

 
     @org.junit.Test
     public void getShortDescription() {
+        CreditCard creditCard = new CreditCard();
+        String getShortDescription = ("CC" + creditCard.getPayerName() + creditCard.getNumber() + creditCard.getExpiredMonth() + "/" + creditCard.getExpiredYear());
+        String expectedGetShortDescription = ("CC" + creditCard.payerName + creditCard.getNumber() + creditCard.getExpiredMonth() + "/" + creditCard.getExpiredYear());
+        String actualGetShortDescription = creditCard.getShortDescription();
+        assertEquals(expectedGetShortDescription, actualGetShortDescription);
+    }
+
+    @Test
+    public void compareTo1() {
+        CreditCard creditCard = new CreditCard();
+        Check check = new Check();
+        int expectedCompareTo = -1;
+        int actualCompareTo = creditCard.compareTo(check);
+        assertEquals(expectedCompareTo, actualCompareTo);
+    }
+
+    @Test
+    public void compareTo2() {
+        CreditCard creditCard = new CreditCard();
+        PayPal payPal = new PayPal();
+        int expectedCompareTo = -1;
+        int actualCompareTo = creditCard.compareTo(payPal);
+        assertEquals(expectedCompareTo, actualCompareTo);
     }
 
+    @Test
+    public void compareTo3() {
+        CreditCard creditCard = new CreditCard();
+        int expectedCompareTo = 0;
+        int actualCompareTo = creditCard.compareTo(creditCard);
+        assertEquals(expectedCompareTo, actualCompareTo);
+    }
 }

src/test/java/com/zipcoder/payment/PayPalTest.java

 
     @Test
     public void getShortDescription() {
+        PayPal payPal = new PayPal();
+        String getShortDescription = ("PayPal" + payPal.payerName + payPal.email);
+         String expectedGetShortDescription = ("PayPal" + payPal.payerName + payPal.email);
+         String actualGetShortDescription = payPal.getShortDescription();
+        assertEquals(expectedGetShortDescription, actualGetShortDescription);
     }
 }