Add an annotation test

Author: WaVEV

tests/annotations_/__init__.py

@@ -0,0 +1,6 @@
+from django.db import models
+
+
+class Book(models.Model):
+    isbn = models.CharField(max_length=9)
+    name = models.CharField(max_length=255)

tests/annotations_/models.py

@@ -0,0 +1,15 @@
+from django.db.models import BooleanField, ExpressionWrapper, IntegerField, Q, Sum
+from django.db.models.functions import Cast
+from django.test import TestCase
+
+from .models import Book
+
+
+class AnnotationTestCase(TestCase):
+    def test_aggregate_over_empty_expression_annotation(self):
+        Book.objects.create(isbn="000", name="book 1")
+        Book.objects.create(isbn="001", name="book 2")
+        qs = Book.objects.annotate(
+            selected=ExpressionWrapper(Q(pk__in=[]), output_field=BooleanField()),
+        ).aggregate(selected__sum=Sum(Cast("selected", IntegerField())))
+        self.assertEqual(qs["selected__sum"], 0)