made some fixtures yield, and restructured django_db_blocker fixture

pytest_django/fixtures.py

@@ -84,7 +84,7 @@ def django_db_createdb(request):
 def django_db_setup(
     request,
     django_test_environment,
-    django_db_blocker,
+    _django_db_blocker,
     django_db_use_migrations,
     django_db_keepdb,
     django_db_createdb,
@@ -101,15 +101,16 @@ def django_db_setup(
     if django_db_keepdb and not django_db_createdb:
         setup_databases_args["keepdb"] = True
 
-    with django_db_blocker.unblock():
+    with _django_db_blocker.unblock():
         db_cfg = setup_databases(
             verbosity=request.config.option.verbose,
             interactive=False,
             **setup_databases_args
         )
 
-    def teardown_database():
-        with django_db_blocker.unblock():
+    yield
+    if not django_db_keepdb:
+        with _django_db_blocker.unblock():
             try:
                 teardown_databases(db_cfg, verbosity=request.config.option.verbose)
             except Exception as exc:
@@ -119,9 +120,6 @@ def teardown_database():
                     )
                 )
 
-    if not django_db_keepdb:
-        request.addfinalizer(teardown_database)
-
 
 def _django_db_fixture_helper(
     request, django_db_blocker, transactional=False, reset_sequences=False
@@ -191,7 +189,7 @@ def _set_suffix_to_test_databases(suffix):
 
 
 @pytest.fixture(scope="function")
-def db(request, django_db_setup, django_db_blocker):
+def db(request, django_db_blocker):
     """Require a django test database.
 
     This database will be setup with the default fixtures and will have
@@ -429,13 +427,15 @@ def _live_server_helper(request):
     It will also override settings only for the duration of the test.
     """
     if "live_server" not in request.fixturenames:
+        yield
         return
 
     request.getfixturevalue("transactional_db")
 
     live_server = request.getfixturevalue("live_server")
     live_server._live_server_modified_settings.enable()
-    request.addfinalizer(live_server._live_server_modified_settings.disable)
+    yield
+    live_server._live_server_modified_settings.disable()
 
 
 @contextmanager

pytest_django/plugin.py

@@ -462,7 +462,7 @@ def django_test_environment(request):
 
 
 @pytest.fixture(scope="session")
-def django_db_blocker():
+def _django_db_blocker():
     """Wrapper around Django's database access.
 
     This object can be used to re-enable database access.  This fixture is used
@@ -481,6 +481,28 @@ def django_db_blocker():
     return _blocking_manager
 
 
+@pytest.fixture(scope="session")
+def django_db_blocker(django_db_setup, _django_db_blocker):
+    """Wrapper around _django_db_blocker to serve as convenience reference.
+
+    The ``_django_db_blocker`` fixture must be available for the ``django_db_setup``
+    fixture, so ``django_db_setup`` must request the ``_django_db_blocker`` fixture. But
+    in order for ``_django_db_blocker`` to be used, ``django_db_setup`` must also have
+    been executed, suggesting that ``_django_db_blocker`` should request
+    ``django_db_setup``, especially since it is possible for ``_django_db_blocker`` to
+    be needed when ``django_db_setup`` wouldn't normally have been run (e.g. if a test
+    isn't marked with ``pytest.mark.django_db``).
+
+    This would normally cause a catch-22, but to circumvent this, the
+    `_django_db_blocker`` fixture is used behind the scenes, while ``django_db_blocker``
+    serves as the fixture used by everything that would normally need the blocker (aside
+    from ``django_db_setup``). This fixture helps coordinate between both
+    ``django_db_setup`` and ``_django_db_blocker``, so that whenever
+    ``django_db_blocker`` gets used, it ensures ``django_db_setup`` is run first.
+    """
+    return _django_db_blocker
+
+
 @pytest.fixture(autouse=True)
 def _django_db_marker(request):
     """Implement the django_db marker, internal to pytest-django.
@@ -500,7 +522,7 @@ def _django_db_marker(request):
 
 
 @pytest.fixture(autouse=True, scope="class")
-def _django_setup_unittest(request, django_db_blocker):
+def _django_setup_unittest(request, _django_db_blocker):
     """Setup a django unittest, internal to pytest-django."""
     if not django_settings_is_configured() or not is_django_unittest(request):
         yield
@@ -525,7 +547,7 @@ def non_debugging_runtest(self):
 
     cls = request.node.cls
 
-    with django_db_blocker.unblock():
+    with _django_db_blocker.unblock():
         if _handle_unittest_methods:
             _restore_class_methods(cls)
             cls.setUpClass()
@@ -736,7 +758,7 @@ def __exit__(self, exc_type, exc_value, traceback):
 class _DatabaseBlocker(object):
     """Manager for django.db.backends.base.base.BaseDatabaseWrapper.
 
-    This is the object returned by django_db_blocker.
+    This is the object returned by _django_db_blocker and django_db_blocker.
     """
 
     def __init__(self):

tests/test_db_access_in_repr.py

@@ -5,7 +5,7 @@ def test_db_access_with_repr_in_report(django_testdir):
 
         from .app.models import Item
 
-        def test_via_db_blocker(django_db_setup, django_db_blocker):
+        def test_via_db_blocker(django_db_blocker):
             with django_db_blocker.unblock():
                 Item.objects.get(name='This one is not there')
 

tests/test_fixtures.py

@@ -617,15 +617,13 @@ def test_block_with_block(self, django_db_blocker):
             with pytest.raises(RuntimeError):
                 Item.objects.exists()
 
-    @pytest.mark.django_db
     def test_unblock_manually(self, django_db_blocker):
         try:
             django_db_blocker.unblock()
             Item.objects.exists()
         finally:
             django_db_blocker.restore()
 
-    @pytest.mark.django_db
     def test_unblock_with_block(self, django_db_blocker):
         with django_db_blocker.unblock():
             Item.objects.exists()