Reorganized comparison db function tests.

tests/db_functions/comparison/test_coalesce.py

@@ -0,0 +1,72 @@
+from django.db.models import TextField
+from django.db.models.functions import Coalesce, Lower
+from django.test import TestCase
+from django.utils import timezone
+
+from ..models import Article, Author
+
+lorem_ipsum = """
+    Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod
+    tempor incididunt ut labore et dolore magna aliqua."""
+
+
+class CoalesceTests(TestCase):
+
+    def test_basic(self):
+        Author.objects.create(name='John Smith', alias='smithj')
+        Author.objects.create(name='Rhonda')
+        authors = Author.objects.annotate(display_name=Coalesce('alias', 'name'))
+        self.assertQuerysetEqual(
+            authors.order_by('name'), ['smithj', 'Rhonda'],
+            lambda a: a.display_name
+        )
+
+    def test_gt_two_expressions(self):
+        with self.assertRaisesMessage(ValueError, 'Coalesce must take at least two expressions'):
+            Author.objects.annotate(display_name=Coalesce('alias'))
+
+    def test_mixed_values(self):
+        a1 = Author.objects.create(name='John Smith', alias='smithj')
+        a2 = Author.objects.create(name='Rhonda')
+        ar1 = Article.objects.create(
+            title='How to Django',
+            text=lorem_ipsum,
+            written=timezone.now(),
+        )
+        ar1.authors.add(a1)
+        ar1.authors.add(a2)
+        # mixed Text and Char
+        article = Article.objects.annotate(
+            headline=Coalesce('summary', 'text', output_field=TextField()),
+        )
+        self.assertQuerysetEqual(
+            article.order_by('title'), [lorem_ipsum],
+            lambda a: a.headline
+        )
+        # mixed Text and Char wrapped
+        article = Article.objects.annotate(
+            headline=Coalesce(Lower('summary'), Lower('text'), output_field=TextField()),
+        )
+        self.assertQuerysetEqual(
+            article.order_by('title'), [lorem_ipsum.lower()],
+            lambda a: a.headline
+        )
+
+    def test_ordering(self):
+        Author.objects.create(name='John Smith', alias='smithj')
+        Author.objects.create(name='Rhonda')
+        authors = Author.objects.order_by(Coalesce('alias', 'name'))
+        self.assertQuerysetEqual(
+            authors, ['Rhonda', 'John Smith'],
+            lambda a: a.name
+        )
+        authors = Author.objects.order_by(Coalesce('alias', 'name').asc())
+        self.assertQuerysetEqual(
+            authors, ['Rhonda', 'John Smith'],
+            lambda a: a.name
+        )
+        authors = Author.objects.order_by(Coalesce('alias', 'name').desc())
+        self.assertQuerysetEqual(
+            authors, ['John Smith', 'Rhonda'],
+            lambda a: a.name
+        )