Correct usage of Flask's app context during testing - fix #90

Don't create an application context during testing.  See #90 for
more info on the reason why this was problematic.  Adjust test
fixtures to compensate.

BREAKING CHANGE
---------------

No longer initializing an app context means that flask.current_app
as well as keg.db.db operations may fail where they did not
previously.  You will need to adjust your test fixtures to either
get the app instance directly or create the app context as needed.

The changes to our tests in this commit will provide good examples
of different kinds of fixture usage that can be used to work around
this change.

keg/app.py

@@ -214,26 +214,27 @@ def environ_key(cls, key):
     @classmethod
     def testing_prep(cls, **config):
         """
-            Make sure an instance of this class exists in a state that is ready for testing to
-            commence.
-
-            Trigger `signal.testing_run_start` the first time this method is called for an app.
+            1. Instantiate the app class.
+            2. Cache the app instance after creation so that it's only instantiated once per Python
+                process.
+            3. Trigger `signal.testing_run_start` the first time this method is called for an app
+                class.
         """
         # For now, do the import here so we don't have a hard dependency on WebTest
         from keg.testing import ContextManager
         if cls is Keg:
             raise TypeError('Don\'t use testing_prep() on Keg.  Create a subclass first.')
         cm = ContextManager.get_for(cls)
 
-        # if the context manager's app isn't ready, that means this will be the first time the app
+        # If the context manager's app isn't ready, that means this will be the first time the app
         # is instantiated.  That seems like a good indicator that tests are just beginning, so it's
         # safe to trigger the signal.  We don't want the signal to fire every time b/c
         # testing_prep() can be called more than once per test run.
-        trigger_signal = not cm.is_ready()
-        cm.ensure_current(config)
-
-        if trigger_signal:
-            signals.testing_run_start.send(cm.app)
+        if not cm.is_ready():
+            app = cm.make_ready(config)
+            # Setup an app context so that DB operations will work without error.
+            with app.app_context():
+                signals.testing_run_start.send(app)
 
         return cm.app
 

keg/testing.py

@@ -6,7 +6,6 @@
 from flask_webtest import TestApp
 import six
 
-from keg import current_app
 from keg.utils import app_environ_get
 
 
@@ -26,23 +25,13 @@ class ContextManager(object):
     def __init__(self, appcls):
         self.appcls = appcls
         self.app = None
-        self.ctx = None
-
-    def ensure_current(self, config):
 
+    def make_ready(self, config):
         if not self.app:
             self.app = self.appcls().init(use_test_profile=True, config=config)
-            self.ctx = self.app.app_context()
-            self.ctx.push()
-
-        if current_app._get_current_object is not self.app:
-            self.ctx.push()
 
         return self.app
 
-    def cleanup(self):
-        self.ctx.pop()
-
     def is_ready(self):
         return self.app is not None
 
@@ -112,4 +101,4 @@ class WebBase(object):
     @classmethod
     def setup_class(cls):
         cls.app = cls.appcls.testing_prep()
-        cls.testapp = TestApp(flask.current_app)
+        cls.testapp = TestApp(cls.app)

keg/tests/test_assets.py

@@ -5,19 +5,23 @@
 import pytest
 import six
 
-import keg
 from keg.assets import AssetManager, AssetException
 from keg_apps.templating.app import TemplatingApp
 
 
-def setup_module(module):
-    TemplatingApp.testing_prep()
+@pytest.fixture(scope='module')
+def app():
+    return TemplatingApp.testing_prep()
+
+
+@pytest.fixture
+def am(app):
+    return AssetManager(app)
 
 
 class TestAssets(object):
 
-    def test_load_related(self):
-        am = AssetManager(keg.current_app)
+    def test_load_related(self, am):
         am.load_related('assets_in_template.html')
 
         assert len(am.content['js']) == 1
@@ -36,14 +40,12 @@ def test_load_related(self):
         )
         assert content.strip() == '/* assets_in_template css file */'
 
-    def test_load_related_none_found(self):
+    def test_load_related_none_found(self, am):
         with pytest.raises(AssetException) as e:
-            am = AssetManager(keg.current_app)
             am.load_related('_not_there.html')
             assert six.text_type(e) == 'Could not find related assets for template: _not_there.html'
 
-    def test_load_single_asset(self):
-        am = AssetManager(keg.current_app)
+    def test_load_single_asset(self, am):
         am.load_related('assets_include_single.html')
 
         assert len(am.content['js']) == 1

keg/tests/test_cli.py

@@ -39,12 +39,12 @@ def test_default_exception_handling(self):
 
 class TestCLI2(CLIBase):
 
-    @classmethod
-    def setup_class(cls):
-        CLIBase.setup_class()
+    @pytest.fixture(scope='class', autouse=True)
+    def setup_app(self):
         # Use this, instead of setting app_cls on the testing class, in order to test that the
         # machinery in place for using the current app is working.
-        CLI2App.testing_prep()
+        with CLI2App.testing_prep().app_context():
+            yield
 
     def test_invoke(self):
         result = self.invoke('hello1')

keg/tests/test_db.py

@@ -11,19 +11,17 @@
 from keg_apps.db2 import DB2App
 
 
-@pytest.fixture(autouse=True)
-def db_session_prep():
-    """
-        Rollback the session after every test.
-    """
-    db.session.rollback()
-
-
 class TestDB(object):
 
-    @classmethod
-    def setup_class(cls):
-        DBApp.testing_prep()
+    @pytest.fixture(scope="class", autouse=True)
+    def setup_app(self):
+        app = DBApp.testing_prep()
+        # Setup an app context that clears itself when this class's tests are finished.
+        with app.app_context():
+            yield
+
+    def teardown(self):
+        db.session.rollback()
 
     def test_primary_db_entity(self):
         assert ents.Blog.query.count() == 0
@@ -57,9 +55,16 @@ def test_init_without_db_binds(self):
 
 
 class TestDatabaseManager(object):
-    @classmethod
-    def setup_class(cls):
-        DBApp.testing_prep()
+
+    @pytest.fixture(scope="class", autouse=True)
+    def setup_app(self):
+        app = DBApp.testing_prep()
+        # Setup an app context that clears itself when this class's tests are finished.
+        with app.app_context():
+            yield
+
+    def teardown(self):
+        db.session.rollback()
 
     def test_db_init_with_clear(self):
         # have to use self here to enable the inner functions to adjust an outer-context variable

keg/tests/test_db_dialects.py

@@ -8,8 +8,12 @@
 from keg_apps.db.app import DBApp
 
 
-def setup_module(module):
-    DBApp.testing_prep()
+@pytest.fixture(scope="module", autouse=True)
+def app():
+    app = DBApp.testing_prep()
+    # Setup an app context that clears itself when this module's tests are finished.
+    with app.app_context():
+        yield
 
 
 @pytest.fixture(autouse=True)
@@ -24,11 +28,6 @@ class DialectExam(object):
     bind_name = None
     obj_names_sql = None
 
-    @classmethod
-    def setup_class(cls):
-        # passing None as the app just because on_testing_start() doesn't use it
-        current_app.db_manager.on_testing_start(None)
-
     @classmethod
     def dialect(cls):
         return current_app.db_manager.bind_dialect(cls.bind_name)

keg/tests/test_templating.py

@@ -6,28 +6,32 @@
 import pytest
 import six
 
-from keg import current_app
 from keg_apps.templating.app import TemplatingApp
 
 
-def setup_module(module):
-    TemplatingApp.testing_prep()
+@pytest.fixture(scope="module")
+def app():
+    return TemplatingApp.testing_prep()
 
 
 class TestAssetsInclude(object):
-    def render(self, filename):
-        template = current_app.jinja_env.get_template(filename)
-        return template.render()
 
-    def setup_method(self, method):
-        self.ctx = current_app.test_request_context()
+    @pytest.fixture(autouse=True)
+    def setup_teardown(self, app):
+        # setup
+        self.ctx = app.test_request_context()
         self.ctx.push()
         self.assets = self.ctx.assets
-
-    def teardown_method(self, method):
+        self.app = app
+        yield
+        # teardown
         self.ctx.pop()
 
-    def test_include(self):
+    def render(self, filename):
+        template = self.app.jinja_env.get_template(filename)
+        return template.render()
+
+    def test_include(self, app):
         resp = self.render('assets_in_template.html')
         assert resp.strip() == ''