[1.6.x] Fixed #19940 -- Made test.runner.setup_databases properly handle aliases for default db.

Thanks simonpercivall.

Backport of 2cbd579efe from master.

django/test/runner.py

@@ -238,6 +238,7 @@ def setup_databases(verbosity, interactive, **kwargs):
     mirrored_aliases = {}
     test_databases = {}
     dependencies = {}
+    default_sig = connections[DEFAULT_DB_ALIAS].creation.test_db_signature()
     for alias in connections:
         connection = connections[alias]
         if connection.settings_dict['TEST_MIRROR']:
@@ -259,7 +260,7 @@ def setup_databases(verbosity, interactive, **kwargs):
                 dependencies[alias] = (
                     connection.settings_dict['TEST_DEPENDENCIES'])
             else:
-                if alias != DEFAULT_DB_ALIAS:
+                if alias != DEFAULT_DB_ALIAS and connection.creation.test_db_signature() != default_sig:
                     dependencies[alias] = connection.settings_dict.get(
                         'TEST_DEPENDENCIES', [DEFAULT_DB_ALIAS])
 

tests/test_runner/tests.py

@@ -290,6 +290,31 @@ class DummyBackendTest(unittest.TestCase):
             db.connections = old_db_connections
 
 
+class AliasedDefaultTestSetupTest(unittest.TestCase):
+    def test_setup_aliased_default_database(self):
+        """
+        Test that setup_datebases() doesn't fail when 'default' is aliased
+        """
+        runner_instance = runner.DiscoverRunner(verbosity=0)
+        old_db_connections = db.connections
+        try:
+            db.connections = db.ConnectionHandler({
+                'default': {
+                    'NAME': 'dummy'
+                },
+                'aliased': {
+                    'NAME': 'dummy'
+                }
+            })
+            old_config = runner_instance.setup_databases()
+            runner_instance.teardown_databases(old_config)
+        except Exception as e:
+            self.fail("setup_databases/teardown_databases unexpectedly raised "
+                      "an error: %s" % e)
+        finally:
+            db.connections = old_db_connections
+
+
 class DeprecationDisplayTest(AdminScriptTestCase):
     # tests for 19546
     def setUp(self):