Test num queries of latest_of_each()

simple_history/tests/tests/test_manager.py

@@ -3,7 +3,7 @@
 
 import django
 from django.contrib.auth import get_user_model
-from django.db import IntegrityError
+from django.db import IntegrityError, connection
 from django.test import TestCase, override_settings, skipUnlessDBFeature
 
 from simple_history.manager import SIMPLE_HISTORY_REVERSE_ATTR_NAME
@@ -151,33 +151,40 @@ def test_historical_query_set(self):
         """
         Demonstrates how the HistoricalQuerySet works to provide as_of functionality.
         """
+        backend = connection.vendor
+        is_mysql = backend == "mysql"
+
         document1 = RankedDocument.objects.create(rank=42)
         document2 = RankedDocument.objects.create(rank=84)
         document2.rank = 51
         document2.save()
         document1.delete()
         t2 = datetime.now()
 
-        # look for historical records, get back a queryset
+        # Look for historical records, get back a queryset
         with self.assertNumQueries(1):
             queryset = RankedDocument.history.filter(history_date__lte=t2)
             self.assertEqual(queryset.count(), 4)
 
-        # only want the most recend records (provided by HistoricalQuerySet)
-        self.assertEqual(queryset.latest_of_each().count(), 2)
+        # Only want the most recent records (provided by HistoricalQuerySet)
+        with self.assertNumQueries(2 if is_mysql else 1):
+            self.assertEqual(queryset.latest_of_each().count(), 2)
 
-        # want to see the instances as of that time?
-        self.assertEqual(queryset.latest_of_each().as_instances().count(), 1)
+        # Want to see the instances as of that time?
+        with self.assertNumQueries(2 if is_mysql else 1):
+            self.assertEqual(queryset.latest_of_each().as_instances().count(), 1)
 
-        # these new methods are idempotent
-        self.assertEqual(
-            queryset.latest_of_each()
-            .latest_of_each()
-            .as_instances()
-            .as_instances()
-            .count(),
-            1,
-        )
+        # These new methods are idempotent
+        # (One extra query per call to `latest_of_each()` when using MySQL)
+        with self.assertNumQueries(3 if is_mysql else 1):
+            self.assertEqual(
+                queryset.latest_of_each()
+                .latest_of_each()
+                .as_instances()
+                .as_instances()
+                .count(),
+                1,
+            )
 
         # that was all the same as calling as_of!
         self.assertEqual(