Updated the addAt(index,data) function & its tests

Author: Prashansa-K

javatests/com/williamfiset/algorithms/datastructures/linkedlist/LinkedListTest.java

@@ -62,6 +62,20 @@ public void testAddLast() {
     list.addLast(5);
     assertEquals(list.size(), 2);
   }
+  
+  @Test
+  public void testAddAt() throws Exception {
+    list.addAt(0, 1);
+    assertEquals(list.size(), 1);
+    list.addAt(1, 2);
+    assertEquals(list.size(), 2);
+    list.addAt(1, 3);
+    assertEquals(list.size(), 3);
+    list.addAt(2, 4);
+    assertEquals(list.size(), 4);
+    list.addAt(1, 8);
+    assertEquals(list.size(), 5);
+  }
 
   @Test
   public void testRemoveFirst() {