Update tests

Author: ArpitSachan

mongoengine/queryset/base.py

@@ -301,14 +301,16 @@ def first(self):
     def last(self):
         """Retrieve the latest object matching the query."""
         if not self._ordering:
-            raise OperationError("Cannot use `last()` without ordering. Use `order_by()` on the queryset first.")
+            raise OperationError(
+                "Cannot use `last()` without ordering. Use `order_by()` on the queryset first."
+            )
 
         queryset = self.clone()
         if self._none or self._empty:
             return None
 
         try:
-            result = queryset[-1]
+            result = queryset[self.count() - 1]
         except IndexError:
             result = None
         return result

tests/queryset/test_queryset.py

@@ -2605,28 +2605,28 @@ def test_last(self):
         person2 = self.Person(name="User A", age=20).save()
         person3 = self.Person(name="User C", age=30).save()
 
-        assert self.Person.objects.order_by('age').last() == person1
-        assert self.Person.objects.order_by('-age').last() == person2
+        assert self.Person.objects.order_by("age").last() == person1
+        assert self.Person.objects.order_by("-age").last() == person2
 
         person2.age = 31
         person2.save()
-        assert self.Person.objects.order_by('-age').last() == person3
-        assert self.Person.objects.order_by('age').last() == person1
+        assert self.Person.objects.order_by("-age").last() == person3
+        assert self.Person.objects.order_by("age").last() == person1
 
         person1.age = 41
         person1.save()
-        assert self.Person.objects.order_by('age').last() == person1
+        assert self.Person.objects.order_by("age").last() == person1
 
-        assert self.Person.objects.order_by('name').last() == person3
+        assert self.Person.objects.order_by("name").last() == person3
 
-        assert self.Person.objects.filter(age__lt=40).order_by('age').last() == person2
-        assert self.Person.objects.filter(age__gt=50).order_by('age').last() is None 
+        assert self.Person.objects.filter(age__lt=40).order_by("age").last() == person2
+        assert self.Person.objects.filter(age__gt=50).order_by("age").last() is None
 
         with pytest.raises(OperationError):
             self.Person.objects.last()
 
-        person4 = self.Person(name="User D", age=30).save()
-        assert self.Person.objects.order_by('-age').last() == person4
+        self.Person(name="User D", age=30).save()
+        assert self.Person.objects.order_by("-age").last() == person3
 
     def test_order_by_optional(self):
         class BlogPost(Document):