test: Add test_linked_list.py

Author: yyossy5

test/test_linked_list.py

@@ -0,0 +1,35 @@
+"""
+Test cases for linked list operations.
+"""
+
+import unittest
+
+from src.linked_list import ListNode, reverse_linked_list
+
+
+class TestLinkedList(unittest.TestCase):
+    def test_reverse_linked_list(self):
+        """Test reversing a normal linked list with multiple nodes [1->2->3]."""
+        head = ListNode(1)
+        head.next = ListNode(2)
+        head.next.next = ListNode(3)
+
+        reversed_head = reverse_linked_list(head)
+
+        self.assertEqual(reversed_head.val, 3)
+        self.assertEqual(reversed_head.next.val, 2)
+        self.assertEqual(reversed_head.next.next.val, 1)
+        self.assertIsNone(reversed_head.next.next.next)
+
+    def test_reverse_single_node(self):
+        """Test reversing a linked list with a single node [1]."""
+        head = ListNode(1)
+        reversed_head = reverse_linked_list(head)
+
+        self.assertEqual(reversed_head.val, 1)
+        self.assertIsNone(reversed_head.next)
+
+    def test_reverse_empty_list(self):
+        """Test reversing an empty linked list."""
+        reversed_head = reverse_linked_list(None)
+        self.assertIsNone(reversed_head)