Store test class on test suite object.

This prevents a mysterious bug in which the tests get confused about
which model class is being referenced in the unit tests.

tests/test_creating.py

@@ -998,9 +998,13 @@ class Tag(self.Base):
             id = Column(Integer, primary_key=True)
             name = Column(Unicode)
 
+        # HACK It seems that if we don't persist the Article class then
+        # the test sometimes gets confused about which Article class is
+        # being referenced in requests made in the test methods below.
+        self.Article = Article
         self.Tag = Tag
         self.Base.metadata.create_all()
-        self.manager.create_api(Article, methods=['POST'])
+        self.manager.create_api(self.Article, methods=['POST'])
         # HACK Need to create APIs for these other models because otherwise
         # we're not able to create the link URLs to them.
         #
@@ -1033,6 +1037,8 @@ def test_create(self):
             }
         }
         response = self.app.post('/api/article', data=dumps(data))
+        print(dir(self.Article))
+        print(response.data)
         assert response.status_code == 201
         document = loads(response.data)
         article = document['data']