Fix cache panel miss counting

The cache panel was not counting misses for the get_many() cache method,
because it assumed that all keys would be present in the returned dict
(with a value of None if not present in the cache) while in reality only
keys present in the cache are present in the returned dict.  Correct the
miss counting logic, and add a test for tracking hits and misses.

Author: living180

debug_toolbar/panels/cache.py

@@ -101,11 +101,12 @@ def _store_call_info(
             else:
                 self.hits += 1
         elif name == "get_many":
-            for key, value in return_value.items():
-                if value is None:
-                    self.misses += 1
-                else:
-                    self.hits += 1
+            if "keys" in kwargs:
+                keys = kwargs["keys"]
+            else:
+                keys = args[0]
+            self.hits += len(return_value)
+            self.misses += len(keys) - len(return_value)
         time_taken *= 1000
 
         self.total_time += time_taken

docs/changes.rst

@@ -8,6 +8,8 @@ Change log
   instances isn't a valid use of Django but, again, django-debug-toolbar
   shouldn't crash.
 * Added pyflame (for flame graphs) to the list of third-party panels.
+* Fixed the cache panel to correctly count cache misses from the get_many()
+  cache method.
 
 3.4.0 (2022-05-03)
 ------------------

tests/panels/test_cache.py

@@ -26,6 +26,23 @@ def test_recording_caches(self):
         second_cache.get("foo")
         self.assertEqual(len(self.panel.calls), 2)
 
+    def test_hits_and_misses(self):
+        cache.cache.clear()
+        cache.cache.get("foo")
+        self.assertEqual(self.panel.hits, 0)
+        self.assertEqual(self.panel.misses, 1)
+        cache.cache.set("foo", 1)
+        cache.cache.get("foo")
+        self.assertEqual(self.panel.hits, 1)
+        self.assertEqual(self.panel.misses, 1)
+        cache.cache.get_many(["foo", "bar"])
+        self.assertEqual(self.panel.hits, 2)
+        self.assertEqual(self.panel.misses, 2)
+        cache.cache.set("bar", 2)
+        cache.cache.get_many(keys=["foo", "bar"])
+        self.assertEqual(self.panel.hits, 4)
+        self.assertEqual(self.panel.misses, 2)
+
     def test_get_or_set_value(self):
         cache.cache.get_or_set("baz", "val")
         self.assertEqual(cache.cache.get("baz"), "val")