Stop using development mode

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Stop using development mode. by @tomstuart, at Railsberry, in Kraków, on 2012-04-20.

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How to develop a Rails application:

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RAILS_ENV=development

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conﬁg/environments/ development.rb: config.cache_classes = false

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$ rails server

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(That was 2005.)

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Development mode is what ﬁrst got me excited about Rails.

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Reload-driven development ™

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What’s wrong with this methodology?

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cowboy programming testless programming inside-out programming it encourages:

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Cowboy programming

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programming before thinking pressing reload until it looks like it’s working writing the code you want to write

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Testless programming

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why write tests when you can press reload?

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PRESSING RELOAD DOESN’T SCALE

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why write tests when you can press reload? the app works! now write tests so you don’t feel guilty the app broke! now write tests so it doesn’t break again

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THE DEFINITION OF WORKING IS THAT THE TESTS PASS

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Inside-out programming

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write a migration write a model write a controller write a template write a route press reload

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database.

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database. model.

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database. model. controller.

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database. model. controller. template.

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database. model. controller. template. route. user.

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You build each layer before you’ve built the layer that uses it.

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You are imagining what the next layer will need this one to do.

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If you love imagining things that much,

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move to Los Angeles

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and become a Scientologist.

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Development mode doesn’t let you see anything working until you’ve completed a full vertical slice through the application.

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This makes it easier to write badly designed code.

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If Rails has a development mode, shouldn’t I use it?

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What’s a “web framework”?

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“A collection of libraries, utilities and conventions to make web application development easier.”

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You are right and good.

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“A note from my mother excusing me from responsibility for every decision.”

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YOUR FAULT YOU ARE WRONG AND BAD EVERYTHING IS

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Rails is software. It doesn’t care about you.

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Be mindful. Use judgement.

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There is a better way.

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Two related ideas:

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1. Work outside-in.

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Start by writing an acceptance test to explain the ultimate goal.

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(An automated one.)

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Drill down into the application by writing unit tests to set intermediate goals.

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Make progress towards the ultimate goal by getting unit tests to pass, not by pressing reload.

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Reach the ultimate goal by getting the acceptance test to pass, not by pressing reload.

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(During development, your primary clients are automated tests, not web browsers.)

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How is this possible? How can you test the controller before writing the model?

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2. Use mocking.

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Ruby is inspired by Smalltalk.

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Smalltalk says: a program is a network of collaborating objects.

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Reboot your brain to think in terms of object collaboration.

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Drive out the design of objects using mocking, not guessing.

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mock these unit test this

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You can implement an object before its collaborators exist.

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By the time you start implementing them, you’ll already know what they need to do.

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It’s not about coverage, it’s about driving your design directly at every level.

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The only limitation is your acceptance tests.

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Some automated tests are too hard, or impossible, to write.

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Fine: use development mode to run those acceptance tests with your eyes and brain.