Reorganized text db function tests.

tests/db_functions/text/test_substr.py

@@ -0,0 +1,53 @@
+from django.db.models import CharField, Value as V
+from django.db.models.functions import Lower, StrIndex, Substr, Upper
+from django.test import TestCase
+
+from ..models import Author
+
+
+class SubstrTests(TestCase):
+
+    def test_basic(self):
+        Author.objects.create(name='John Smith', alias='smithj')
+        Author.objects.create(name='Rhonda')
+        authors = Author.objects.annotate(name_part=Substr('name', 5, 3))
+        self.assertQuerysetEqual(
+            authors.order_by('name'), [' Sm', 'da'],
+            lambda a: a.name_part
+        )
+        authors = Author.objects.annotate(name_part=Substr('name', 2))
+        self.assertQuerysetEqual(
+            authors.order_by('name'), ['ohn Smith', 'honda'],
+            lambda a: a.name_part
+        )
+        # If alias is null, set to first 5 lower characters of the name.
+        Author.objects.filter(alias__isnull=True).update(
+            alias=Lower(Substr('name', 1, 5)),
+        )
+        self.assertQuerysetEqual(
+            authors.order_by('name'), ['smithj', 'rhond'],
+            lambda a: a.alias
+        )
+
+    def test_start(self):
+        Author.objects.create(name='John Smith', alias='smithj')
+        a = Author.objects.annotate(
+            name_part_1=Substr('name', 1),
+            name_part_2=Substr('name', 2),
+        ).get(alias='smithj')
+
+        self.assertEqual(a.name_part_1[1:], a.name_part_2)
+
+    def test_pos_gt_zero(self):
+        with self.assertRaisesMessage(ValueError, "'pos' must be greater than 0"):
+            Author.objects.annotate(raises=Substr('name', 0))
+
+    def test_expressions(self):
+        Author.objects.create(name='John Smith', alias='smithj')
+        Author.objects.create(name='Rhonda')
+        substr = Substr(Upper('name'), StrIndex('name', V('h')), 5, output_field=CharField())
+        authors = Author.objects.annotate(name_part=substr)
+        self.assertQuerysetEqual(
+            authors.order_by('name'), ['HN SM', 'HONDA'],
+            lambda a: a.name_part
+        )