We started this chapter by first introducing the concept of an application factory and described some of the benefits and trade-offs of this approach. Next, we used our newly created application factory to set up our first test suite using py.test, which required some modification as to how our application object was created in order to ensure that we obtained a suitable instance that was configured to test scenarios.

Then, we dove headfirst into implementing the basic data models behind a typical web application that contained social features with the ability to follow other users and be followed ourselves. We briefly touched on several main implementation patterns for so-called newsfeed applications and used the simplest version for our own data models.

This then led us to discuss and explore the concept of the publish/subscribe design pattern, of which an in-process implementation can be found in the Blinker package that Flask and various Flask extensions integrate. Using this new...