Add support for serialized rollback

Author: luzfcb

.gitignore

@@ -16,3 +16,4 @@ _build
 .Python
 .eggs
 *.egg
+.idea/

docs/changelog.rst

@@ -1,6 +1,17 @@
 Changelog
 =========
 
+NEXT
+----
+
+Features
+^^^^^^^^
+* Add support for serialized rollback in transactional tests. (#721)
+  Thanks to Piotr Karkut for `the bug report
+  <https://github.com/pytest-dev/pytest-django/issues/329>`_.
+
+
+
 3.6.0 (2019-10-17)
 ------------------
 

docs/helpers.rst

@@ -16,7 +16,7 @@ on what marks are and for notes on using_ them.
 ``pytest.mark.django_db`` - request database access
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-.. :py:function:: pytest.mark.django_db([transaction=False, reset_sequences=False]):
+.. :py:function:: pytest.mark.django_db([transaction=False, reset_sequences=False, serialized_rollback=False]):
 
 This is used to mark a test function as requiring the database. It
 will ensure the database is set up correctly for the test. Each test
@@ -47,6 +47,14 @@ test will fail when trying to access the database.
  effect.  Please be aware that not all databases support this feature.
  For details see :py:attr:`django.test.TransactionTestCase.reset_sequences`.
 
+:type serialized_rollback: bool
+:param serialized_rollback:
+ The ``serialized_rollback`` argument enables `rollback emulation`_.
+ After a `django.test.TransactionTestCase`_ runs, the database is
+ flushed, destroying data created in data migrations. This is the
+ default behavior of Django. Setting ``serialized_rollback=True``
+ tells Django to restore that data.
+
 .. note::
 
   If you want access to the Django database *inside a fixture*
@@ -63,6 +71,7 @@ test will fail when trying to access the database.
  Test classes that subclass Python's ``unittest.TestCase`` need to have the
  marker applied in order to access the database.
 
+.. _rollback emulation: https://docs.djangoproject.com/en/stable/topics/testing/overview/#rollback-emulation
 .. _django.test.TestCase: https://docs.djangoproject.com/en/dev/topics/testing/overview/#testcase
 .. _django.test.TransactionTestCase: https://docs.djangoproject.com/en/dev/topics/testing/overview/#transactiontestcase
 
@@ -242,6 +251,17 @@ sequences (if your database supports it). This is only required for
 fixtures which need database access themselves. A test function should
 normally use the ``pytest.mark.django_db`` mark with ``transaction=True`` and ``reset_sequences=True``.
 
+``django_db_serialized_rollback``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+ When the ``transactional_db`` fixture is enabled, this fixture can be
+added to trigger `rollback emulation`_ and thus restores data created
+in data migrations after each transaction test.  This is only required
+for fixtures which need to enforce this behavior.  A test function
+would use :py:func:`~pytest.mark.django_db(serialized_rollback=True)`
+to request this behavior.
+
+
 ``live_server``
 ~~~~~~~~~~~~~~~
 
@@ -251,6 +271,12 @@ or by requesting it's string value: ``unicode(live_server)``.  You can
 also directly concatenate a string to form a URL: ``live_server +
 '/foo``.
 
+Since the live server and the tests run in different threads, they
+cannot share a database transaction. For this reason, ``live_server``
+depends on the ``transactional_db`` fixture. If tests depend on data
+created in data migrations, you should add the ``serialized_rollback``
+fixture.
+
 .. note:: Combining database access fixtures.
 
   When using multiple database fixtures together, only one of them is

pytest_django/fixtures.py

@@ -18,6 +18,7 @@
     "db",
     "transactional_db",
     "django_db_reset_sequences",
+    "django_db_serialized_rollback",
     "admin_user",
     "django_user_model",
     "django_username_field",
@@ -124,7 +125,8 @@ def teardown_database():
 
 
 def _django_db_fixture_helper(
-    request, django_db_blocker, transactional=False, reset_sequences=False
+    request, django_db_blocker, transactional=False, reset_sequences=False,
+    serialized_rollback=False
 ):
     if is_django_unittest(request):
         return
@@ -149,6 +151,7 @@ class ResetSequenceTestCase(django_case):
         from django.test import TestCase as django_case
 
     test_case = django_case(methodName="__init__")
+    test_case.serialized_rollback = serialized_rollback
     test_case._pre_setup()
     request.addfinalizer(test_case._post_teardown)
 
@@ -207,13 +210,16 @@ def db(request, django_db_setup, django_db_blocker):
     """
     if "django_db_reset_sequences" in request.fixturenames:
         request.getfixturevalue("django_db_reset_sequences")
+    if "django_db_serialized_rollback" in request.fixturenames:
+        request.getfixturevalue("django_db_serialized_rollback")
     if (
         "transactional_db" in request.fixturenames
         or "live_server" in request.fixturenames
     ):
         request.getfixturevalue("transactional_db")
     else:
-        _django_db_fixture_helper(request, django_db_blocker, transactional=False)
+        _django_db_fixture_helper(request, django_db_blocker, transactional=False,
+                                  serialized_rollback=False)
 
 
 @pytest.fixture(scope="function")
@@ -232,6 +238,8 @@ def transactional_db(request, django_db_setup, django_db_blocker):
     """
     if "django_db_reset_sequences" in request.fixturenames:
         request.getfixturevalue("django_db_reset_sequences")
+    if "django_db_serialized_rollback" in request.fixturenames:
+        request.getfixturevalue("django_db_serialized_rollback")
     _django_db_fixture_helper(request, django_db_blocker, transactional=True)
 
 
@@ -253,6 +261,20 @@ def django_db_reset_sequences(request, django_db_setup, django_db_blocker):
     )
 
 
+@pytest.fixture(scope="function")
+def django_db_serialized_rollback(request, django_db_setup, django_db_blocker):
+    """Enable serialized rollback after transaction test cases
+
+    This fixture only has an effect when the ``transactional_db``
+    fixture is active, which happen as a side-effect of requesting
+    ``live_server``.
+
+    """
+    _django_db_fixture_helper(
+        request, django_db_blocker, transactional=True, serialized_rollback=True
+    )
+
+
 @pytest.fixture()
 def client():
     """A Django test client instance."""

pytest_django/plugin.py

@@ -34,6 +34,7 @@
 from .fixtures import django_username_field  # noqa
 from .fixtures import live_server  # noqa
 from .fixtures import django_db_reset_sequences  # noqa
+from .fixtures import django_db_serialized_rollback  # noqa
 from .fixtures import rf  # noqa
 from .fixtures import settings  # noqa
 from .fixtures import transactional_db  # noqa
@@ -497,14 +498,17 @@ def django_db_blocker():
 def _django_db_marker(request):
     """Implement the django_db marker, internal to pytest-django.
 
-    This will dynamically request the ``db``, ``transactional_db`` or
-    ``django_db_reset_sequences`` fixtures as required by the django_db marker.
+    This will dynamically request the ``db``, ``transactional_db``,
+    ``django_db_reset_sequences`` or ``django_db_serialized_rollback``
+     fixtures as required by the django_db marker.
     """
     marker = request.node.get_closest_marker("django_db")
     if marker:
-        transaction, reset_sequences = validate_django_db(marker)
+        transaction, reset_sequences, serialized_rollback = validate_django_db(marker)
         if reset_sequences:
             request.getfixturevalue("django_db_reset_sequences")
+        elif serialized_rollback:
+            request.getfixturevalue("django_db_serialized_rollback")
         elif transaction:
             request.getfixturevalue("transactional_db")
         else:
@@ -805,15 +809,16 @@ def restore(self):
 def validate_django_db(marker):
     """Validate the django_db marker.
 
-    It checks the signature and creates the ``transaction`` and
-    ``reset_sequences`` attributes on the marker which will have the
-    correct values.
+    It checks the signature and creates the ``transaction``,
+    ``reset_sequences`` and ``serialized_rollback`` attributes on
+    the marker which will have the correct values.
 
     A sequence reset is only allowed when combined with a transaction.
+    A serialized rollback is only allowed when combined with a transaction.
     """
 
-    def apifun(transaction=False, reset_sequences=False):
-        return transaction, reset_sequences
+    def apifun(transaction=False, reset_sequences=False, serialized_rollback=False):
+        return transaction, reset_sequences, serialized_rollback
 
     return apifun(*marker.args, **marker.kwargs)
 

tests/test_database.py

@@ -50,10 +50,13 @@ def non_zero_sequences_counter(db):
 class TestDatabaseFixtures:
     """Tests for the different database fixtures."""
 
-    @pytest.fixture(params=["db", "transactional_db", "django_db_reset_sequences"])
+    @pytest.fixture(params=["db", "transactional_db", "django_db_reset_sequences",
+                            "django_db_serialized_rollback"])
     def all_dbs(self, request):
         if request.param == "django_db_reset_sequences":
             return request.getfixturevalue("django_db_reset_sequences")
+        elif request.param == "django_db_serialized_rollback":
+            return request.getfixturevalue("django_db_serialized_rollback")
         elif request.param == "transactional_db":
             return request.getfixturevalue("transactional_db")
         elif request.param == "db":
@@ -215,6 +218,16 @@ def test_reset_sequences_enabled(self, request):
         marker = request.node.get_closest_marker("django_db")
         assert marker.kwargs["reset_sequences"]
 
+    @pytest.mark.django_db
+    def test_serialized_rollback_disabled(self, request):
+        marker = request.node.get_closest_marker("django_db")
+        assert not marker.kwargs
+
+    @pytest.mark.django_db(serialized_rollback=True)
+    def test_serialized_rollback_enabled(self, request):
+        marker = request.node.get_closest_marker("django_db")
+        assert marker.kwargs["serialized_rollback"]
+
 
 def test_unittest_interaction(django_testdir):
     "Test that (non-Django) unittests cannot access the DB."