2 files changed, 99 insertions, 3 deletions
diff --git a/tests/test_utils/models.py b/tests/test_utils/models.py
index c40801f81b..b0497f12b9 100644
--- a/tests/test_utils/models.py
+++ b/tests/test_utils/models.py
@@ -12,4 +12,4 @@ class Person(models.Model):
 
 class PossessedCar(models.Model):
     car = models.ForeignKey(Car, models.CASCADE)
-    belongs_to = models.ForeignKey(Person, models.CASCADE)
+    belongs_to = models.ForeignKey(Person, models.CASCADE, related_name='possessed_cars')
diff --git a/tests/test_utils/test_testcase.py b/tests/test_utils/test_testcase.py
index 853aba7c22..5ec71f84d0 100644
--- a/tests/test_utils/test_testcase.py
+++ b/tests/test_utils/test_testcase.py
@@ -1,7 +1,11 @@
+from functools import wraps
+
 from django.db import IntegrityError, connections, transaction
-from django.test import TestCase, skipUnlessDBFeature
+from django.test import TestCase, ignore_warnings, skipUnlessDBFeature
+from django.test.testcases import TestData
+from django.utils.deprecation import RemovedInDjango41Warning
 
-from .models import Car, PossessedCar
+from .models import Car, Person, PossessedCar
 
 
 class TestTestCase(TestCase):
@@ -38,3 +42,95 @@ class TestTestCase(TestCase):
         )
         with self.assertRaisesMessage(AssertionError, message):
             Car.objects.using('other').get()
+
+
+class NonDeepCopyAble:
+    def __deepcopy__(self, memo):
+        raise TypeError
+
+
+def assert_no_queries(test):
+    @wraps(test)
+    def inner(self):
+        with self.assertNumQueries(0):
+            test(self)
+    return inner
+
+
+class TestDataTests(TestCase):
+    # setUpTestData re-assignment are also wrapped in TestData.
+    jim_douglas = None
+
+    @classmethod
+    def setUpTestData(cls):
+        cls.jim_douglas = Person.objects.create(name='Jim Douglas')
+        cls.car = Car.objects.create(name='1963 Volkswagen Beetle')
+        cls.herbie = cls.jim_douglas.possessed_cars.create(
+            car=cls.car,
+            belongs_to=cls.jim_douglas,
+        )
+        cls.non_deepcopy_able = NonDeepCopyAble()
+
+    @assert_no_queries
+    def test_class_attribute_equality(self):
+        """Class level test data is equal to instance level test data."""
+        self.assertEqual(self.jim_douglas, self.__class__.jim_douglas)
+
+    @assert_no_queries
+    def test_class_attribute_identity(self):
+        """
+        Class level test data is not identical to instance level test data.
+        """
+        self.assertIsNot(self.jim_douglas, self.__class__.jim_douglas)
+
+    @assert_no_queries
+    def test_identity_preservation(self):
+        """Identity of test data is preserved between accesses."""
+        self.assertIs(self.jim_douglas, self.jim_douglas)
+
+    @assert_no_queries
+    def test_known_related_objects_identity_preservation(self):
+        """Known related objects identity is preserved."""
+        self.assertIs(self.herbie.car, self.car)
+        self.assertIs(self.herbie.belongs_to, self.jim_douglas)
+
+    @ignore_warnings(category=RemovedInDjango41Warning)
+    def test_undeepcopyable(self):
+        self.assertIs(self.non_deepcopy_able, self.__class__.non_deepcopy_able)
+
+    def test_undeepcopyable_warning(self):
+        msg = (
+            "Assigning objects which don't support copy.deepcopy() during "
+            "setUpTestData() is deprecated. Either assign the "
+            "non_deepcopy_able attribute during setUpClass() or setUp(), or "
+            "add support for deepcopy() to "
+            "test_utils.test_testcase.TestDataTests.non_deepcopy_able."
+        )
+        with self.assertRaisesMessage(RemovedInDjango41Warning, msg):
+            self.non_deepcopy_able
+
+    def test_repr(self):
+        self.assertEqual(
+            repr(TestData('attr', 'value')),
+            "<TestData: name='attr', data='value'>",
+        )
+
+
+class SetupTestDataIsolationTests(TestCase):
+    """
+    In-memory data isolation is respected for model instances assigned to class
+    attributes during setUpTestData.
+    """
+    @classmethod
+    def setUpTestData(cls):
+        cls.car = Car.objects.create(name='Volkswagen Beetle')
+
+    def test_book_name_deutsh(self):
+        self.assertEqual(self.car.name, 'Volkswagen Beetle')
+        self.car.name = 'VW sKäfer'
+        self.car.save()
+
+    def test_book_name_french(self):
+        self.assertEqual(self.car.name, 'Volkswagen Beetle')
+        self.car.name = 'Volkswagen Coccinelle'
+        self.car.save()