Web Applications

Good magic, bad magic

Philip Potter pinged me his post on Sinatra magic during the week. Mark Needham’s comment and code on solving the mocking problem is good advice to the problem as posed.

At Wazoku where we use the often equally magical Bottle framework we don’t use top-down TDD but instead outside-in functional tests (with no funky runners as we don’t need CI). This solves the whole magic issue by shifting the attention to what the public interactions of the application are. This is one of the massive benefits of using a microapp HTTP/JSON/REST-like architecture. I could flip the API from Bottle to Django or Compojure or Sinatra and my test suite can keep on rocking and telling me whether the behaviour my consumers are relying on is correct.

The major thing I felt when reading through Philip’s post was the massive amount of effort that was going into testing relatively simple behaviour. This is a bit of anti-pattern with Agile developers (or perhaps it is part of the mastery thing where rote “correct” behaviour is modified by experience and judgement). One of the massive advantages of using something like Sinatra is that you can get a whole web app with rich behaviour into less than 200 lines. If you then create thousands of lines of test code and battle with the magic for hours on end you’ve completely destroyed your productivity.

If you have a code base that you expect to be large and highly contested by a large development team you need good, layered testing and to use frameworks that support that. If you have an app that is small and when its done it is done then there is no need to agonise as to whether it was done “right”.

The idea that top-down TDD is the only correct way to write software is corrosive. When faced with a generally poorly skilled and educated workforce it is good to have rules. I have imposed a certain style of TDD on a group myself because it gives a good framework for work and achieves very consistent output.

However with skilled people on small scale projects you can kill yourself by imposing arbitrary rules. I love Sinatra and while I might be equivocal about magic I think it is ridiculous to moan about it if you are using something as unicorn-packed as Ruby. For example Philip was trying to use RSpec mocks and stubs to do his TDD. The result is kind of saying that you’re disappointed that your “good” magic for testing didn’t work with the “bad” magic of a DSL for web applications. Even if your RSpec code passed its tests you still haven’t said anything particularly deep about the production behaviour of your application as your unit testing environment was severely compromised by the manipulations of your mocking framework.

So my rule of thumb is: if its simple, do it; if it was simple, functionally test it; if it was never really simple then test-drive it with suitable tools.

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