Added the starting point of a linked_list implementation with tests.

Author: sbauer

.vscode/settings.json

@@ -0,0 +1,4 @@
+{
+    "python.linting.enabled": false,
+    "python.pythonPath": "/usr/local/bin/python3.6"
+}

__init__.py

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+class Node(object):
+    def __init__(self, data, next = None):
+        self.next = next
+        self.data = data
+
+class LinkedList(object):
+    def __init__(self, head = None):
+        self.head = head
+
+    def insert(self, data):
+        new_head = Node(data, self.head)
+        self.head = new_head
+
+    def append(self, data):
+        new_node = Node(data)
+        
+        if self.head is None:
+            self.head = new_node
+            return
+        
+        current_node = self.head
+
+        while current_node.next is not None:
+            current_node = current_node.next
+
+        current_node.next = new_node
+
+
+    def is_empty(self):
+        return self.head == None

linked_lists/linked_list.py

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+import unittest
+from linked_list import *
+
+class LinkedListTests(unittest.TestCase):
+
+    def test_empty_list_should_have_no_head(self):
+        list = LinkedList()
+        self.assertIsNone(list.head)
+
+    def test_adding_one_value_should_create_head(self):
+        list = LinkedList()
+        list.insert("First")
+        self.assertIsNotNone(list.head)
+        self.assertEqual(list.head.data, "First")
+
+    def test_inserting_second_value_should_replace_head(self):
+        list = LinkedList()
+        list.insert("First")
+        list.insert("Second")
+        self.assertEqual(list.head.data, "Second")
+
+    def test_inserting_second_value_should_move_existing_head_to_next(self):
+        list = LinkedList()
+        list.insert("First")
+        list.insert("Second")
+        self.assertEqual(list.head.next.data, "First")
+
+    def test_appending_first_value_should_set_head(self):
+        list = LinkedList()
+        list.append("First")
+        self.assertEqual(list.head.data, "First")
+
+    def test_appending_second_value_should_set_head_next(self):
+        list = LinkedList()
+        list.append("First")
+        list.append("Second")
+        self.assertEqual(list.head.next.data, "Second")
+
+    def test_is_empty_should_be_true_if_no_head(self):
+        list = LinkedList()
+        self.assertTrue(list.is_empty())
+
+if __name__ == '__main__':
+    unittest.main()