fix: ensure config has no app when constructor finishes

had to move `make_engine_from_config()` out of app handler and define
as a separate function, so that `get_engines()` did not need to
instantiate the app handler.  because if it did, then config
extensions would lose the ability to set a default app handler - er,
they could do it but it would be ignored

tests/db/test_conf.py

@@ -7,6 +7,8 @@ from unittest import TestCase
 
 import sqlalchemy as sa
 from sqlalchemy import orm
+from sqlalchemy.engine import Engine
+from sqlalchemy.pool import NullPool
 
 from wuttjamaican.db import conf
 from wuttjamaican.conf import WuttaConfig
@@ -93,3 +95,38 @@ class TestGetSetting(TestCase):
     def test_missing_value(self):
         value = conf.get_setting(self.session, 'foo')
         self.assertIsNone(value)
+
+
+class TestMakeEngineFromConfig(TestCase):
+
+    def test_basic(self):
+        engine = conf.make_engine_from_config({
+            'sqlalchemy.url': 'sqlite://',
+        })
+        self.assertIsInstance(engine, Engine)
+
+    def test_poolclass(self):
+
+        engine = conf.make_engine_from_config({
+            'sqlalchemy.url': 'sqlite://',
+        })
+        self.assertNotIsInstance(engine.pool, NullPool)
+
+        engine = conf.make_engine_from_config({
+            'sqlalchemy.url': 'sqlite://',
+            'sqlalchemy.poolclass': 'sqlalchemy.pool:NullPool',
+        })
+        self.assertIsInstance(engine.pool, NullPool)
+
+    def test_pool_pre_ping(self):
+
+        engine = conf.make_engine_from_config({
+            'sqlalchemy.url': 'sqlite://',
+        })
+        self.assertFalse(engine.pool._pre_ping)
+
+        engine = conf.make_engine_from_config({
+            'sqlalchemy.url': 'sqlite://',
+            'sqlalchemy.pool_pre_ping': 'true',
+        })
+        self.assertTrue(engine.pool._pre_ping)

tests/test_app.py

@@ -9,8 +9,6 @@ from unittest.mock import patch, MagicMock
 
 import sqlalchemy as sa
 from sqlalchemy import orm
-from sqlalchemy.engine import Engine
-from sqlalchemy.pool import NullPool
 
 from wuttjamaican import app, db
 from wuttjamaican.conf import WuttaConfig
@@ -47,38 +45,6 @@ class TestAppHandler(TestCase):
         self.assertEqual(len(os.listdir(tempdir)), 3)
         shutil.rmtree(tempdir)
 
-    def test_make_engine_from_config_basic(self):
-        engine = self.app.make_engine_from_config({
-            'sqlalchemy.url': 'sqlite://',
-        })
-        self.assertIsInstance(engine, Engine)
-
-    def test_make_engine_from_config_poolclass(self):
-
-        engine = self.app.make_engine_from_config({
-            'sqlalchemy.url': 'sqlite://',
-        })
-        self.assertNotIsInstance(engine.pool, NullPool)
-
-        engine = self.app.make_engine_from_config({
-            'sqlalchemy.url': 'sqlite://',
-            'sqlalchemy.poolclass': 'sqlalchemy.pool:NullPool',
-        })
-        self.assertIsInstance(engine.pool, NullPool)
-
-    def test_make_engine_from_config_pool_pre_ping(self):
-
-        engine = self.app.make_engine_from_config({
-            'sqlalchemy.url': 'sqlite://',
-        })
-        self.assertFalse(engine.pool._pre_ping)
-
-        engine = self.app.make_engine_from_config({
-            'sqlalchemy.url': 'sqlite://',
-            'sqlalchemy.pool_pre_ping': 'true',
-        })
-        self.assertTrue(engine.pool._pre_ping)
-
     def test_make_session(self):
         session = self.app.make_session()
         self.assertIsInstance(session, db.Session.class_)
@@ -118,7 +84,7 @@ class TestAppProvider(TestCase):
     def setUp(self):
         self.config = WuttaConfig(appname='wuttatest')
         self.app = app.AppHandler(self.config)
-        self.config.app = self.app
+        self.config._app = self.app
 
     def test_constructor(self):
 
@@ -198,7 +164,7 @@ class TestGenericHandler(TestCase):
     def setUp(self):
         self.config = WuttaConfig(appname='wuttatest')
         self.app = app.AppHandler(self.config)
-        self.config.app = self.app
+        self.config._app = self.app
 
     def test_constructor(self):
         handler = app.GenericHandler(self.config)

tests/test_conf.py

@@ -228,6 +228,17 @@ configure_logging = true
             config = conf.WuttaConfig(files=[myfile])
             logging.config.fileConfig.assert_called_once()
 
+    def test_config_has_no_app_after_init(self):
+
+        # initial config should *not* have an app yet, otherwise
+        # extensions cannot specify a default app handler
+        config = conf.WuttaConfig()
+        self.assertFalse(hasattr(config, '_app'))
+
+        # but after that we can get an app okay
+        app = config.get_app()
+        self.assertIs(app, config._app)
+
     def test_setdefault(self):
         config = conf.WuttaConfig()