Making your test doubles more resilient.
Once, a younger brother came to him, and asked, "Father, I have made and kept my little rule, my fast, my meditation and silence. I strived to cleanse my heart of thoughts, what more must I do?" The elder rose up and, stretched out his hands, his fingers became like ten lamps ablaze. He said, "Why not be totally changed into fire?" -- Desert Way, Charlie Hunter
Test doubles are sweet for isolating your unit tests, but we lost something in the translation from typed languages. Ruby doesn't have a compiler that can verify the contracts being mocked out are indeed legit. This hurts larger refactorings, since you can totally change a collaborator --- renaming methods, changing the number of arguments --- and all the mocks that were standing in for it will keep pretending everything is ok.
rspec-fire mitigates that problem, with very little change to your existing
One solution would be to disallow stubbing of methods that don't exist. This is
what mocha does with its
Mocha::Configuration.prevent(:stubbing_non_existent_method) option. The
downside is, you now have to load the collaborators/dependencies that you are
mocking, which kind of defeats the purpose of isolated testing. Not ideal.
Another solution, that
rspec-fire adopts, is a more relaxed version that only
checks that the methods exist if the doubled class has already been loaded.
No checking will happen when running the spec in isolation, but when run in the
context of the full app (either as a full spec run or by explicitly preloading
collaborators on the command line) a failure will be triggered if an invalid
method is being stubbed.
It's a gem!
gem install rspec-fire
Bit of setup in your
require 'rspec/fire' RSpec.configure do |config| config.include(RSpec::Fire) end
Specify the class being doubled in your specs:
class User < Struct.new(:notifier) def suspend! notifier.notify("suspended as") end end describe User, '#suspend!' do it 'sends a notification' do # Only this one line differs from how you write specs normally notifier = fire_double("EmailNotifier") notifier.should_receive(:notify).with("suspended as") user = User.new(notifier) user.suspend! end end
Run your specs:
# Isolated, will pass always rspec spec/user_spec.rb # Will fail if EmailNotifier#notify method is not defined rspec -Ilib/email_notifier.rb spec/user_spec.rb
Method presence/absence is checked, and if a
with is provided then so is
Using with an existing Rails project
Create a new file
unit_helper.rb that does not require
Require this file where needed for isolated tests. To run an isolated spec in
the context of your app:
rspec -r./spec/spec_helper.rb spec/unit/my_spec.rb
Using with ActiveRecord
ActiveRecord methods defined implicitly from database columns are not detected. A workaround is to explicitly define the methods you are mocking:
class User < ActiveRecord::Base # Explicit column definitions for rspec-fire def name; super; end def email; super; end end
A particularly excellent feature. You can stub out constants using
fire_replaced_class_double, removing the need to dependency inject
collaborators (a technique that can sometimes be cumbersome).
class User def suspend! EmailNotifier.notify("suspended as") end end describe User, '#suspend!' do it 'sends a notification' do # Only this one line differs from how you write specs normally notifier = fire_replaced_class_double("EmailNotifier") # Alternately, you can use this fluent interface notifier = fire_class_double("EmailNotifier").as_replaced_constant notifier.should_receive(:notify).with("suspended as") user = User.new user.suspend! end end
This will probably become the default behaviour once we figure out a better name for it.
The constant stubbing logic used when doubling class constants can be used for any constant.
class MapReduceRunner ITEMS_PER_BATCH = 1000 end describe MapReduceRunner, "when it has too many items for one batch" do it "breaks the items up into smaller batches" do # the test would be really slow if we had to make more than 1000 items, # so let's change the threshold for this one test. stub_const("MapReduceRunner::ITEMS_PER_BATCH", 10) MapReduceRunner.run_with(twenty_items) end end
Transferring nested constants to doubled constants
When you use
fire_replaced_class_double to replace a class or module
that also acts as a namespace for other classes and constants, your
access to these constants is cut off for the duration of the example
(since the doubled constant does not automatically have all of the
nested constants). The
:transfer_nested_constants option is provided
to deal with this:
module MyCoolGem class Widget end end # once you do this, you can no longer access MyCoolGem::Widget in your example... fire_replaced_class_double("MyCoolGem") # ...unless you tell rspec-fire to transfer all nested constants fire_class_double("MyCoolGem").as_replaced_constant(:transfer_nested_constants => true) # ...or give it a list of constants to transfer fire_class_double("MyCoolGem").as_replaced_constant(:transfer_nested_constants => [:Widget]) # You can also use this when using #stub_const directly stub_const("MyCoolGem", :transfer_nested_constants => true)
Doubling class methods
Particularly handy for
ActiveRecord finders. Use
fire_class_double. If you
dig into the code, you'll find you can create subclasses of
check for any set of methods.
Mocking Done Right (tm)
- Only mock methods on collaborators, not the class under test.
- Only mock public methods.
If you can't meet these criteria, your object is probably violating SOLID principles and you should either refactor or use a non-isolated test.
Only RSpec 2 is supported. Tested on all the rubies thanks to Travis CI.
git clone https://github.com/xaviershay/rspec-fire.git bundle install bundle exec rake spec
Patches welcome! I won't merge anything that isn't spec'ed, but I can help you out with that if you are getting stuck.
Still need to support
rspec-fire is pretty new and not used widely. Yet.