added reverselookup

src/main/java/com/zipcodewilmington/phonebook/PhoneBook.java

 
  public String lookup(String name){
         return contacts.get(name);
-
  }
 
  public String listNames(){
         StringBuilder namesnumbers = new StringBuilder();
         Set<String> keys = contacts.keySet();
         for(String key: keys)
-
         {
-
             namesnumbers.append(key+" "+contacts.get(key)+"\n");
         }
         return namesnumbers.toString();
     }
 
+    public String reverselookup(String number){
+        Set<String> names = contacts.keySet();
+        for(String name: names)
+        {
+            if (contacts.get(name).equals(number)){
+                return name;
+            }
+        }
+        return null;
+    }
+
+
 
 }

src/test/java/com/zipcodewilmington/phonebook/PhoneBookTest.java

         String actual = testbook.listNames();
         Assert.assertEquals(expected, actual);
     }
-
-
+    @Test
+    public void testPhoneBookReverseLookUp() {
+        PhoneBook testbook = new PhoneBook();
+        testbook.add("Keith", "555-666-7777");
+        testbook.add("John", "555-612-7777");
+        testbook.add("Mike", "555-623-7777");
+        testbook.add("Steve", "555-645-7777");
+        String testnumber = testbook.reverselookup("555-666-7777");
+        Assert.assertEquals("Keith", testnumber);
+    }
 }