fix(cache): preserve get defaults and LRU order

Author: Vl4dC

aws_lambda_powertools/shared/cache_dict.py

@@ -3,8 +3,8 @@
 
 class LRUDict(OrderedDict):
     """
-    Cache implementation based on ordered dict with a maximum number of items. Last accessed item will be evicted
-    first. Currently used by idempotency utility.
+    Cache implementation based on ordered dict with a maximum number of items. Least recently used item will be
+    evicted first. Currently used by idempotency utility.
     """
 
     def __init__(self, max_items=1024, *args, **kwargs):
@@ -26,6 +26,6 @@ def __setitem__(self, key, value):
 
     def get(self, key, *args, **kwargs):
         item = super().get(key, *args, **kwargs)
-        if item:
+        if key in self:
             self.move_to_end(key=key)
         return item

tests/unit/test_lru_cache.py

@@ -43,6 +43,26 @@ def test_cache_order_get(populated_cache):
     assert last_item == f"key_{random_value}"
 
 
+def test_cache_get_missing_key_returns_default():
+    cache = LRUDict(max_items=2)
+    cache["existing"] = "value"
+
+    assert cache.get("missing", "fallback") == "fallback"
+    assert list(cache) == ["existing"]
+
+
+@pytest.mark.parametrize("value", [False, 0, None, ""])
+def test_cache_get_falsey_value_updates_recency(value):
+    cache = LRUDict(max_items=2)
+    cache["falsey"] = value
+    cache["other"] = "value"
+
+    assert cache.get("falsey") == value
+    cache["new"] = "value"
+
+    assert list(cache) == ["falsey", "new"]
+
+
 def test_cache_evict_over_max_items(populated_cache):
     assert "key_0" in populated_cache
     assert len(populated_cache) == MAX_CACHE_ITEMS