diff --git a/linked-lists/kth-to-last-elem.ipynb b/linked-lists/kth-to-last-elem.ipynb
index c9de9c5..444dab5 100644
--- a/linked-lists/kth-to-last-elem.ipynb
+++ b/linked-lists/kth-to-last-elem.ipynb
@@ -13,26 +13,31 @@
    "source": [
     "## Problem: Find the kth to last element of a linked list\n",
     "\n",
-    "* [Clarifying Questions](#Clarifying-Questions)\n",
+    "* [Constraints and Assumptions](#Constraints-and-Assumptions)\n",
     "* [Test Cases](#Test-Cases)\n",
     "* [Algorithm](#Algorithm)\n",
-    "* [Code](#Code)"
+    "* [Code](#Code)\n",
+    "* [Unit Test](#Unit-Test)"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Clarifying Questions\n",
+    "## Constraints and Assumptions\n",
     "\n",
-    "* Is k an integer?\n",
+    "*Problem statements are often intentionally ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
+    "\n",
+    "* Can we assume k is a valid integer?\n",
     "    * Yes\n",
     "* If k = 0, does this return the last element?\n",
     "    * Yes\n",
     "* What happens if k is greater than or equal to the length of the linked list?\n",
     "    * Return None\n",
     "* Can you use additional data structures?\n",
-    "    * No"
+    "    * No\n",
+    "* Can we assume we already have a linked list class that can be used for this problem?\n",
+    "    * Yes"
    ]
   },
   {
@@ -54,7 +59,6 @@
    "source": [
     "## Algorithm\n",
     "\n",
-    "* Check for edge cases above, returning None for errors\n",
     "* Setup two pointers, current and previous\n",
     "* Give current a headstart, incrementing it once for k = 1, twice for k = 2, etc\n",
     "* Increment both pointers until current reaches the end\n",
@@ -74,7 +78,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 1,
    "metadata": {
     "collapsed": true
    },
@@ -85,7 +89,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 2,
    "metadata": {
     "collapsed": false
    },
@@ -95,49 +99,89 @@
     "    def kth_to_last_elem(self, k):\n",
     "        if self.head is None:\n",
     "            return\n",
-    "        if type(k) != int:\n",
-    "            raise ValueError('')\n",
     "        if k >= len(self):\n",
     "            return\n",
     "        curr = self.head\n",
     "        prev = self.head\n",
     "        counter = 0\n",
+    "        \n",
+    "        # Give current a headstart, incrementing it \n",
+    "        # once for k = 1, twice for k = 2, etc\n",
     "        while counter < k:\n",
     "            curr = curr.next\n",
     "            counter += 1\n",
     "            if curr is None:\n",
     "                return\n",
+    "            \n",
+    "        # Increment both pointers until current reaches the end\n",
     "        while curr.next is not None:\n",
     "            curr = curr.next\n",
     "            prev = prev.next\n",
     "        return prev.data"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "*It is important to identify and run through general and edge cases from the [Test Cases](#Test-Cases) section by hand.  You generally will not be asked to write a unit test like what is shown below.*"
+   ]
+  },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 3,
    "metadata": {
     "collapsed": false
    },
-   "outputs": [],
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Test: Empty list\n",
+      "Test: k >= len(list)\n",
+      "Test: One element, k = 0\n",
+      "Test: General case\n",
+      "Success: test_kth_to_last_elem\n"
+     ]
+    }
+   ],
    "source": [
-    "# Empty list\n",
-    "linked_list = MyLinkedList(None)\n",
-    "print(linked_list.kth_to_last_elem(0))\n",
-    "# k is not an integer\n",
-    "print(linked_list.kth_to_last_elem('a'))\n",
-    "# k is >= the length of the linked list\n",
-    "print(linked_list.kth_to_last_elem(100))\n",
-    "# One element, k = 0\n",
-    "head = Node(2)\n",
-    "linked_list = MyLinkedList(head)\n",
-    "print(linked_list.kth_to_last_elem(0))\n",
-    "# General case with many elements, k < length of linked list\n",
-    "linked_list.insert_to_front(1)\n",
-    "linked_list.insert_to_front(3)\n",
-    "linked_list.insert_to_front(5)\n",
-    "linked_list.insert_to_front(7)\n",
-    "print(linked_list.kth_to_last_elem(2))"
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "class Test(object):\n",
+    "    def test_kth_to_last_elem(self):\n",
+    "        print('Test: Empty list')\n",
+    "        linked_list = MyLinkedList(None)\n",
+    "        assert_equal(linked_list.kth_to_last_elem(0), None)\n",
+    "        \n",
+    "        print('Test: k >= len(list)')\n",
+    "        assert_equal(linked_list.kth_to_last_elem(100), None)\n",
+    "        \n",
+    "        print('Test: One element, k = 0')\n",
+    "        head = Node(2)\n",
+    "        linked_list = MyLinkedList(head)\n",
+    "        assert_equal(linked_list.kth_to_last_elem(0), 2)\n",
+    "        \n",
+    "        print('Test: General case')\n",
+    "        linked_list.insert_to_front(1)\n",
+    "        linked_list.insert_to_front(3)\n",
+    "        linked_list.insert_to_front(5)\n",
+    "        linked_list.insert_to_front(7)\n",
+    "        assert_equal(linked_list.kth_to_last_elem(2), 3)\n",
+    "        \n",
+    "        print('Success: test_kth_to_last_elem')\n",
+    "\n",
+    "if __name__ == '__main__':\n",
+    "    test = Test()\n",
+    "    test.test_kth_to_last_elem()"
    ]
   }
  ],