Developing Upwards

In Part 1 I wrote about my method of testing the actual tag function for a custom Django template tag. I said I would follow it with a Part 2 on testing the rendering of the resulting Node . This is that follow up post for any of you who were waiting for it. Testing the rendering poses some more problems than our little tag function. Rendering is going to do a bit more, including loading the templates, resolving any variables in question, doing any processing on those results (like looking up a record from the database based on the variable value), and finally populating a new context to render the tag's template with. How do we test all of that, without actually doing any of that? This is the goal we're reaching here, for unittests. We want each test to be so specific that we test what something will do, without actually relying on those things it does. We aren't testing any of those things, just that our render() method does them. What can we mock easily? get_te...

This is an index of different articles I've written covering techniques for testing specific software components. The number is small, but will grow in time. Initially, expect a heavier lean towards Django topics. How To Test Django Template Tags Parts One and Two

I'm involved in a project that has gone for a long time without tests and everyone involved knows tests are rilly rilly important . There is a point where acknowledged best practices simply meets the reality of the development mind and it doesn't always work out like you'd hope. We know tests are important, but we need to resolve this ticket right freaking now . You understand. The point was reached that this just couldn't continue and the costs of fixing the same bugs over and over were way too obvious to ignore. Tests are now popping up for things we're fixing and new things we're writing. As it happens, I came across my first real need to create a custom template tag. Of course, I wanted to test it. So how do you test something that is so entrenched in the Django processing pipeline as a template tag? Incidentally, I'm just going to assume you either know all about testing and Django template tags or you can follow along just fine. Testing breaks ...

I'm toying with the idea of a new way to write tests. This is a cross between state and interaction based testing, and also tries to make setting up the test environments easier. I call it "Flow Testing" as it tests how the various states of the test target flow from one to the next. The idea is several-fold. We begin on the idea that we are testing names, because everything in Python starts with a name. You will test different things about names, such as type, what attributes or other properties apply to certain conditions, etc. Flow testing is very tree-oriented. For every name, you define the state you expect to begin, and branch into the state you expect for various properties. For example, you may have a state for the name 'foo' and a branch state for 'foo.bar'. These are branches within one state, while wthere are other branches across states called Interaction Branches. These states define the interactions that lead to them and the states expected. ...

Good testing influences your design. Too many developers (and managers) are stuck in the waterfall mentality of design, code, test, and deploy. Forces across the industry are pushing to move the testing phase to the beginning of this line, and many just don't understand how that works. Testing should be the first consideration, and thus is influential to all other aspects of the development process. The problem with testing as a secondary consideration is the design and architecture of the software never lends itself to proper testing when you don't plan way ahead. The consideration of testing can drive your design to be easier to test, but also can encourage generally good programming practices and well-made designs in the architecture. We can use a persisted class as a good example, because this is a use-case where testing is very important, but we have to consider the burden of a full database tied into the class we are testing. When we develop our database item class befor...