test: add edge case and complex value tests for LruCache

- Verify that updating existing keys correctly refreshes their MRU status
- Test edge case for a cache with a limit of one
- Add test for retrieving non-existent keys (returning None)
- Confirm support for complex data types like lists and dictionaries

Author: Iswanna

Sprint-2/implement_lru_cache/lru_cache_test.py

@@ -54,6 +54,40 @@ def test_eviction_order_after_gets(self):
         self.assertEqual(cache.get("a"), 1)
         self.assertEqual(cache.get("c"), 3)
 
+    def test_update_existing_key(self):
+        cache = LruCache(limit=2)
+        cache.set("a", 1)
+        cache.set("b", 2)
+        
+        # Update "a" - it should stay in the cache but change value
+        cache.set("a", 100)
+        self.assertEqual(cache.get("a"), 100)
+        
+        # Adding "c" should now evict "b", because "a" was recently updated
+        cache.set("c", 3)
+        self.assertIsNone(cache.get("b"))
+        self.assertEqual(cache.get("a"), 100)
+
+    def test_limit_of_one(self):
+        cache = LruCache(limit=1)
+        cache.set("a", 1)
+        self.assertEqual(cache.get("a"), 1)
+        
+        cache.set("b", 2) # This should immediately kick out "a"
+        self.assertIsNone(cache.get("a"))
+        self.assertEqual(cache.get("b"), 2)
+
+    def test_get_non_existent_key(self):
+        cache = LruCache(limit=5)
+        # Testing "None" return for keys never added
+        self.assertIsNone(cache.get("missing_key"))
+
+    def test_complex_values(self):
+        cache = LruCache(limit=2)
+        # Testing that we can store lists or dictionaries, not just strings
+        cache.set("list", [1, 2, 3])
+        self.assertEqual(cache.get("list"), [1, 2, 3])
+
 
 if __name__ == "__main__":
     unittest.main()