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Rails special sauce: Test::Unit setup and teardown


Rails adds plenty of special sauce to Ruby standard library.

Being a fan of testing and all that, let me show you what I found while spelunking around the Rails supporting test cases:

The revelation

module ActionMailer
  class TestCase < ActiveSupport::TestCase
    setup :initialize_test_deliveries
    protected
      def initialize_test_deliveries
        # ... snip ...
      end
    # ... snip ...
  end
end

The shock

What the?!?! I thought you had to def setup for setup methods…. but here, it’s a method call, that takes a symbol.

The realization

This reminds me of something

class Subscription < ActiveRecord::Base
  before_create :record_signup

  private
    def record_signup
      self.signed_up_on = Date.today
    end
end

Shocking to say, but they are similar, because they both use ActiveSupport::Callbacks. Basically, this allows us to specify setup and teardown blocks the same way we’ve been specifying ActionController filters and ActiveRecord callbacks:

  • Using a method name as a symbol
  • Using a block
  • Using a method
  • Using conditions
  • Determined by a lambda
  • Determined by a method name as a symbol

The experiment

Let’s try using these all together:

require 'rubygems'
require 'active_support'
require 'active_support/test_case'
require 'test/unit'

class ExampleTest < Test::Unit::TestCase
  def setup
    puts "called from def setup"
  end
  
  setup :setup_with_symbol
  setup :setup_never_called, :if => :never
  setup :setup_never_called, :if => lambda { false }

  setup do
    puts "called from a block"
  end
  
  def setup_with_symbol
    puts "called by using symbol of a method name"
  end
  
  def test_nothing
    puts "I am testing nothing"
    assert true
  end
  
  def setup_never_called
    flunk "Should never be displayed"
  end
  
  def never
    false
  end
end

This outputs:

Loaded suite test-test
Started
called by using symbol of a method name
called from a setup block
called from def setup
I am testing nothing
.
Finished in 0.000371 seconds.

1 tests, 1 assertions, 0 failures, 0 errors

The conclusion

So why is this significant?

  • Isolate related setup into their own methods
  • Have setup and teardown be conditionally done
  • Allows superclasses to give default setup and teardown, while allowing subclasses to have their own, without needing to call super
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