Fixed #20579 -- Improved TransactionTestCase.available_apps.

Also moved its documentation to the 'advanced' section. It doesn't
belong to the 'overview'. Same for TransactionTestCase.reset_sequences.

When available_apps is set, after a TransactionTestCase, the database
is now totally empty. post_syncdb is fired at the beginning of the next
TransactionTestCase.

Refs #20483.

2 files changed, 40 insertions, 23 deletions

diff --git a/django/core/management/commands/flush.py b/django/core/management/commands/flush.py
index 7054187e45..95dd634d08 100644
--- a/django/core/management/commands/flush.py
+++ b/django/core/management/commands/flush.py
@@ -32,9 +32,10 @@ class Command(NoArgsCommand):
         connection = connections[db]
         verbosity = int(options.get('verbosity'))
         interactive = options.get('interactive')
-        # 'reset_sequences' and 'allow_cascade' are stealth options
+        # The following are stealth options used by Django's internals.
         reset_sequences = options.get('reset_sequences', True)
         allow_cascade = options.get('allow_cascade', False)
+        inhibit_post_syncdb = options.get('inhibit_post_syncdb', False)
 
         self.style = no_style()
 
@@ -75,16 +76,9 @@ Are you sure you want to do this?
                     "Hint: Look at the output of 'django-admin.py sqlflush'. That's the SQL this command wasn't able to run.\n"
                     "The full error: %s") % (connection.settings_dict['NAME'], e)
                 six.reraise(CommandError, CommandError(new_msg), sys.exc_info()[2])
-            # Emit the post sync signal. This allows individual
-            # applications to respond as if the database had been
-            # sync'd from scratch.
-            all_models = []
-            for app in models.get_apps():
-                all_models.extend([
-                    m for m in models.get_models(app, include_auto_created=True)
-                    if router.allow_syncdb(db, m)
-                ])
-            emit_post_sync_signal(set(all_models), verbosity, interactive, db)
+
+            if not inhibit_post_syncdb:
+                self.emit_post_syncdb(verbosity, interactive, db)
 
             # Reinstall the initial_data fixture.
             if options.get('load_initial_data'):
@@ -93,3 +87,15 @@ Are you sure you want to do this?
 
         else:
             self.stdout.write("Flush cancelled.\n")
+
+    @staticmethod
+    def emit_post_syncdb(verbosity, interactive, database):
+        # Emit the post sync signal. This allows individual applications to
+        # respond as if the database had been sync'd from scratch.
+        all_models = []
+        for app in models.get_apps():
+            all_models.extend([
+                m for m in models.get_models(app, include_auto_created=True)
+                if router.allow_syncdb(database, m)
+            ])
+        emit_post_sync_signal(set(all_models), verbosity, interactive, database)
diff --git a/django/test/testcases.py b/django/test/testcases.py
index 1dbb82e352..984d21ce18 100644
--- a/django/test/testcases.py
+++ b/django/test/testcases.py
@@ -24,6 +24,7 @@ from django.core.exceptions import ValidationError, ImproperlyConfigured
 from django.core.handlers.wsgi import WSGIHandler
 from django.core.management import call_command
 from django.core.management.color import no_style
+from django.core.management.commands import flush
 from django.core.servers.basehttp import (WSGIRequestHandler, WSGIServer,
     WSGIServerException)
 from django.core.urlresolvers import clear_url_caches, set_urlconf
@@ -196,9 +197,9 @@ class SimpleTestCase(ut2.TestCase):
     def _pre_setup(self):
         """Performs any pre-test setup. This includes:
 
-           * If the Test Case class has a 'urls' member, replace the
-             ROOT_URLCONF with it.
-           * Clearing the mail test outbox.
+        * Creating a test client.
+        * If the class has a 'urls' attribute, replace ROOT_URLCONF with it.
+        * Clearing the mail test outbox.
         """
         self.client = self.client_class()
         self._urlconf_setup()
@@ -212,6 +213,10 @@ class SimpleTestCase(ut2.TestCase):
             clear_url_caches()
 
     def _post_teardown(self):
+        """Performs any post-test things. This includes:
+
+        * Putting back the original ROOT_URLCONF if it was changed.
+        """
         self._urlconf_teardown()
 
     def _urlconf_teardown(self):
@@ -732,13 +737,17 @@ class TransactionTestCase(SimpleTestCase):
     def _pre_setup(self):
         """Performs any pre-test setup. This includes:
 
-           * Flushing the database.
-           * If the Test Case class has a 'fixtures' member, installing the
-             named fixtures.
+        * If the class has an 'available_apps' attribute, restricting the app
+          cache to these applications, then firing post_syncdb -- it must run
+          with the correct set of applications for the test case.
+        * If the class has a 'fixtures' attribute, installing these fixtures.
         """
         super(TransactionTestCase, self)._pre_setup()
         if self.available_apps is not None:
             cache.set_available_apps(self.available_apps)
+            for db_name in self._databases_names(include_mirrors=False):
+                flush.Command.emit_post_syncdb(
+                        verbosity=0, interactive=False, database=db_name)
         try:
             self._fixture_setup()
         except Exception:
@@ -782,9 +791,9 @@ class TransactionTestCase(SimpleTestCase):
     def _post_teardown(self):
         """Performs any post-test things. This includes:
 
-           * Putting back the original ROOT_URLCONF if it was changed.
-           * Force closing the connection, so that the next test gets
-             a clean cursor.
+        * Flushing the contents of the database, to leave a clean slate. If
+          the class has an 'available_apps' attribute, post_syncdb isn't fired.
+        * Force-closing the connection, so the next test gets a clean cursor.
         """
         try:
             self._fixture_teardown()
@@ -801,12 +810,14 @@ class TransactionTestCase(SimpleTestCase):
             cache.unset_available_apps()
 
     def _fixture_teardown(self):
-        # Allow TRUNCATE ... CASCADE when flushing only a subset of the apps
-        allow_cascade = self.available_apps is not None
+        # Allow TRUNCATE ... CASCADE and don't emit the post_syncdb signal
+        # when flushing only a subset of the apps
         for db_name in self._databases_names(include_mirrors=False):
             call_command('flush', verbosity=0, interactive=False,
                          database=db_name, skip_validation=True,
-                         reset_sequences=False, allow_cascade=allow_cascade)
+                         reset_sequences=False,
+                         allow_cascade=self.available_apps is not None,
+                         inhibit_post_syncdb=self.available_apps is not None)
 
     def assertQuerysetEqual(self, qs, values, transform=repr, ordered=True):
         items = six.moves.map(transform, qs)