Avoided transaction.set_autocommit in tests.

It doesn't work as one might expect on a certain database backend where
autocommits_when_autocommit_is_off = True. That backend happens to be
popular for running tests.

Backport of 38bc581bc0 from master.

tests/backends/tests.py

@@ -640,8 +640,7 @@ class FkConstraintsTests(TransactionTestCase):
         """
         When constraint checks are disabled, should be able to write bad data without IntegrityErrors.
         """
-        transaction.set_autocommit(False)
-        try:
+        with transaction.atomic():
             # Create an Article.
             models.Article.objects.create(headline="Test article", pub_date=datetime.datetime(2010, 9, 4), reporter=self.r)
             # Retrive it from the DB
@@ -653,17 +652,13 @@ class FkConstraintsTests(TransactionTestCase):
                 connection.enable_constraint_checking()
             except IntegrityError:
                 self.fail("IntegrityError should not have occurred.")
-            finally:
-                transaction.rollback()
-        finally:
-            transaction.set_autocommit(True)
+            transaction.set_rollback(True)
 
     def test_disable_constraint_checks_context_manager(self):
         """
         When constraint checks are disabled (using context manager), should be able to write bad data without IntegrityErrors.
         """
-        transaction.set_autocommit(False)
-        try:
+        with transaction.atomic():
             # Create an Article.
             models.Article.objects.create(headline="Test article", pub_date=datetime.datetime(2010, 9, 4), reporter=self.r)
             # Retrive it from the DB
@@ -674,31 +669,23 @@ class FkConstraintsTests(TransactionTestCase):
                     a.save()
             except IntegrityError:
                 self.fail("IntegrityError should not have occurred.")
-            finally:
-                transaction.rollback()
-        finally:
-            transaction.set_autocommit(True)
+            transaction.set_rollback(True)
 
     def test_check_constraints(self):
         """
         Constraint checks should raise an IntegrityError when bad data is in the DB.
         """
-        try:
-            transaction.set_autocommit(False)
+        with transaction.atomic():
             # Create an Article.
             models.Article.objects.create(headline="Test article", pub_date=datetime.datetime(2010, 9, 4), reporter=self.r)
             # Retrive it from the DB
             a = models.Article.objects.get(headline="Test article")
             a.reporter_id = 30
-            try:
-                with connection.constraint_checks_disabled():
-                    a.save()
-                    with self.assertRaises(IntegrityError):
-                        connection.check_constraints()
-            finally:
-                transaction.rollback()
-        finally:
-            transaction.set_autocommit(True)
+            with connection.constraint_checks_disabled():
+                a.save()
+                with self.assertRaises(IntegrityError):
+                    connection.check_constraints()
+            transaction.set_rollback(True)
 
 
 class ThreadTests(TestCase):

tests/fixtures_model_package/tests.py

@@ -30,8 +30,7 @@ class TestNoInitialDataLoading(TransactionTestCase):
     available_apps = ['fixtures_model_package']
 
     def test_syncdb(self):
-        transaction.set_autocommit(False)
-        try:
+        with transaction.atomic():
             Book.objects.all().delete()
 
             management.call_command(
@@ -40,9 +39,6 @@ class TestNoInitialDataLoading(TransactionTestCase):
                 load_initial_data=False
             )
             self.assertQuerysetEqual(Book.objects.all(), [])
-            transaction.rollback()
-        finally:
-            transaction.set_autocommit(True)
 
 
     def test_flush(self):
@@ -54,8 +50,7 @@ class TestNoInitialDataLoading(TransactionTestCase):
             lambda a: a.name
         )
 
-        transaction.set_autocommit(False)
-        try:
+        with transaction.atomic():
             management.call_command(
                 'flush',
                 verbosity=0,
@@ -63,9 +58,6 @@ class TestNoInitialDataLoading(TransactionTestCase):
                 load_initial_data=False
             )
             self.assertQuerysetEqual(Book.objects.all(), [])
-            transaction.rollback()
-        finally:
-            transaction.set_autocommit(True)
 
 
 class FixtureTestCase(TestCase):

tests/fixtures_regress/tests.py

@@ -660,22 +660,15 @@ class TestTicket11101(TransactionTestCase):
         'django.contrib.contenttypes',
     ]
 
-    def ticket_11101(self):
-        management.call_command(
-            'loaddata',
-            'thingy.json',
-            verbosity=0,
-        )
-        self.assertEqual(Thingy.objects.count(), 1)
-        transaction.rollback()
-        self.assertEqual(Thingy.objects.count(), 0)
-        transaction.commit()
-
     @skipUnlessDBFeature('supports_transactions')
     def test_ticket_11101(self):
         """Test that fixtures can be rolled back (ticket #11101)."""
-        transaction.set_autocommit(False)
-        try:
-            self.ticket_11101()
-        finally:
-            transaction.set_autocommit(True)
+        with transaction.atomic():
+            management.call_command(
+                'loaddata',
+                'thingy.json',
+                verbosity=0,
+            )
+            self.assertEqual(Thingy.objects.count(), 1)
+            transaction.set_rollback(True)
+        self.assertEqual(Thingy.objects.count(), 0)