Things added

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

@@ -2,6 +2,6 @@ package com.zipcoder.payment;
 
 public class PaymentPresenter {
 
-
+    public
 
 }

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

@@ -0,0 +1,16 @@
+package com.zipcoder.payment;
+
+import java.util.Comparator;
+
+public class PaymentSortByPayer implements Comparator<Payment> {
+
+    public int compare(Payment o1, Payment o2) {
+        if(o1.getPayerName().compareTo(o2.getPayerName()) > 0){
+            return 1;
+        } else if(o1.getPayerName().compareTo(o2.getPayerName()) < 0){
+            return -1;
+        } else {
+            return 0;
+        }
+    }
+}

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

@@ -1,4 +1,23 @@
 package com.zipcoder.payment;
 
-public class PaymentPresenterTest {
+import org.junit.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+class PaymentPresenterTest {
+
+    @Test
+    void emptyTestOne() {
+        //When
+        Payment[] payments = new Payment[0];
+        PaymentPresenter presenter = new PaymentPresenter();
+
+        //Expect
+        String expected = "";
+
+        //Actual
+        String actual = presenter.toString(payments);
+
+        assertEquals(expected, actual);
+    }
+
 }

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

@@ -0,0 +1,56 @@
+package com.zipcoder.payment;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class PaymentSortByPayerTest {
+
+    @Test
+    void compairTest1() {
+        //When
+        PaymentSortByPayer ps = new PaymentSortByPayer();
+        Payment cc = new CreditCard(12, 4111131,"Jimmy Maidanos", 4, 11);
+        Payment pp = new Paypal(23, "Nicholas Maidanos", "nmaidanos@gmail.com");
+
+        //Expect
+        int expect = -1;
+
+        //Actual
+        int actual = ps.compare(cc, pp);
+
+        assertEquals(expect, actual);
+    }
+
+    @Test
+    void compairTest2() {
+        //When
+        PaymentSortByPayer ps = new PaymentSortByPayer();
+        Payment cc = new CreditCard(12, 4111131,"Zimmy Maidanos", 4, 11);
+        Payment pp = new Paypal(23, "Nicholas Maidanos", "nmaidanos@gmail.com");
+
+        //Expect
+        int expect = 1;
+
+        //Actual
+        int actual = ps.compare(cc, pp);
+
+        assertEquals(expect, actual);
+    }
+
+    @Test
+    void compairTest3() {
+        //When
+        PaymentSortByPayer ps = new PaymentSortByPayer();
+        Payment cc = new CreditCard(12, 4111131,"Nicholas Maidanos", 4, 11);
+        Payment pp = new Paypal(23, "Nicholas Maidanos", "nmaidanos@gmail.com");
+
+        //Expect
+        int expect = 0;
+
+        //Actual
+        int actual = ps.compare(cc, pp);
+
+        assertEquals(expect, actual);
+    }
+}