Fixed #29979, Refs #17337 -- Extracted AutoField field logic into a mixin and refactored AutoFields.

This reduces duplication by allowing AutoField, BigAutoField and
SmallAutoField to inherit from IntegerField, BigIntegerField and
SmallIntegerField respectively. Doing so also allows for enabling the
max_length warning check and minimum/maximum value validation for auto
fields, as well as providing a mixin that can be used for other possible
future auto field types such as a theoretical UUIDAutoField.

4 files changed, 41 insertions, 23 deletions

diff --git a/tests/invalid_models_tests/test_ordinary_fields.py b/tests/invalid_models_tests/test_ordinary_fields.py
index a3231ee36a..5bb1847a70 100644
--- a/tests/invalid_models_tests/test_ordinary_fields.py
+++ b/tests/invalid_models_tests/test_ordinary_fields.py
@@ -38,6 +38,21 @@ class AutoFieldTests(SimpleTestCase):
             ),
         ])
 
+    def test_max_length_warning(self):
+        class Model(models.Model):
+            auto = models.AutoField(primary_key=True, max_length=2)
+
+        field = Model._meta.get_field('auto')
+        self.assertEqual(field.check(), [
+            DjangoWarning(
+                "'max_length' is ignored when used with %s."
+                % field.__class__.__name__,
+                hint="Remove 'max_length' from field",
+                obj=field,
+                id='fields.W122',
+            ),
+        ])
+
 
 @isolate_apps('invalid_models_tests')
 class BinaryFieldTests(SimpleTestCase):
diff --git a/tests/model_fields/test_autofield.py b/tests/model_fields/test_autofield.py
index 73220ae62b..db8e79e34b 100644
--- a/tests/model_fields/test_autofield.py
+++ b/tests/model_fields/test_autofield.py
@@ -1,32 +1,32 @@
-from django.test import TestCase
+from django.db import models
+from django.test import SimpleTestCase
 
 from .models import AutoModel, BigAutoModel, SmallAutoModel
+from .test_integerfield import (
+    BigIntegerFieldTests, IntegerFieldTests, SmallIntegerFieldTests,
+)
 
 
-class AutoFieldTests(TestCase):
+class AutoFieldTests(IntegerFieldTests):
     model = AutoModel
 
-    def test_invalid_value(self):
-        tests = [
-            (TypeError, ()),
-            (TypeError, []),
-            (TypeError, {}),
-            (TypeError, set()),
-            (TypeError, object()),
-            (TypeError, complex()),
-            (ValueError, 'non-numeric string'),
-            (ValueError, b'non-numeric byte-string'),
-        ]
-        for exception, value in tests:
-            with self.subTest(value=value):
-                msg = "Field 'value' expected a number but got %r." % (value,)
-                with self.assertRaisesMessage(exception, msg):
-                    self.model.objects.create(value=value)
 
-
-class BigAutoFieldTests(AutoFieldTests):
+class BigAutoFieldTests(BigIntegerFieldTests):
     model = BigAutoModel
 
 
-class SmallAutoFieldTests(AutoFieldTests):
+class SmallAutoFieldTests(SmallIntegerFieldTests):
     model = SmallAutoModel
+
+
+class AutoFieldInheritanceTests(SimpleTestCase):
+
+    def test_isinstance_of_autofield(self):
+        for field in (models.BigAutoField, models.SmallAutoField):
+            with self.subTest(field.__name__):
+                self.assertIsInstance(field(), models.AutoField)
+
+    def test_issubclass_of_autofield(self):
+        for field in (models.BigAutoField, models.SmallAutoField):
+            with self.subTest(field.__name__):
+                self.assertTrue(issubclass(field, models.AutoField))
diff --git a/tests/model_fields/test_integerfield.py b/tests/model_fields/test_integerfield.py
index c72cb48015..c0bb7627cf 100644
--- a/tests/model_fields/test_integerfield.py
+++ b/tests/model_fields/test_integerfield.py
@@ -125,7 +125,7 @@ class IntegerFieldTests(TestCase):
                         ranged_value_field.run_validators(max_backend_value + 1)
 
     def test_types(self):
-        instance = self.model(value=0)
+        instance = self.model(value=1)
         self.assertIsInstance(instance.value, int)
         instance.save()
         self.assertIsInstance(instance.value, int)
diff --git a/tests/validation/models.py b/tests/validation/models.py
index 953370bc37..e8e18cfbce 100644
--- a/tests/validation/models.py
+++ b/tests/validation/models.py
@@ -130,4 +130,7 @@ try:
         auto2 = models.AutoField(primary_key=True)
 except AssertionError as exc:
     assertion_error = exc
-assert str(assertion_error) == "Model validation.MultipleAutoFields can't have more than one AutoField."
+assert str(assertion_error) == (
+    "Model validation.MultipleAutoFields can't have more than one "
+    "auto-generated field."
+)