VerifiedDouble

VerifiedDouble would record any mock made in the test suite. It would then verify if the mock is valid by checking if there is a test against it.

For example, let's say I mocked the save method of a model like so:

item = VerifiedDouble.of_instance(Item)
item.should_receive(:save).and_return(true)

Calling VerifiedDouble.of_instance would record the :save interaction on item. When running the tests, the gem would look for a test that confirms if you can indeed call #save on Item. The test should also ensure that the method indeed returns a boolean value. Since this is hard to automate, the gem would just look for a test with the tag saying it verifies that contract:

it "tests something", verifies_contract: 'Item#save => Boolean' do
  #...
end

If this test does not exist, the gem would complain that the mock is not verified.

This is an implementation of contract tests. Notes about the presentation here.

There's already a gem that implements contract tests (bogus). However, I think there's room for an alternative because:

It's not clear from the Bogus documentation whether the gem verifies actual arguments/return values or just the types of those values. While the argument/return types are enough in most cases, sometimes the actual argument/return values are important. For example, if I mock Item.where(conditions), the actual conditions are important in verifying the validity of the where call.
By design, a Bogus fake would return itself to all its methods. I prefer rspec-mock's approach of raising an error if a method is not declared as part of the double, since this raises errors earlier than later.

Installation

Add this line to your application's Gemfile:

gem 'verified_double'

And then execute:

$ bundle

Or install it yourself as:

$ gem install verified_double

Contributing

Fork it
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Add some feature')
Push to the branch (git push origin my-new-feature)
Create new Pull Request