dweebd

A little-known and very useful feature Rails brings to the table in terms of testing is a pair of callback hooks for Test::Unit::TestCase setup and teardown.

The callback chains were introduced as part of the move toward a custom ActiveSupport::TestCase, but all the functionality of ActiveSupport::TestCase is exposed to Test::Unit::TestCase if you’re running Rails.

Having these hooks exposed allows you to inject setup and teardown behavior without stepping on the toes of any individual test.

class Test::Unit::TestCase
  def self.does_not_perform_validations klass
    setup do
      @preserved_validations = klass.validate.clone
      klass.validate.clear
    end
    teardown do
      @preserved_validations.each do |validation|
        klass.validate << validation
      end
    end
  end
end

Obviously this example is a little contrived, but perhaps you see how this can be used.

class MarshmallowTest < Test::Unit::TestCase
  does_not_perform_validations Marshmallow
  …
end

Now with a single macro, we can inject setup and teardown behavior for a model. The same technique can be used to inject teardown hooks from within individual tests, but beware, hooks injected in this way need to remove themselves from the callback chain when executing, or else they’ll be executed for every subsequent test teardown.