Simplified illustrative example of 'collaboration' tests between two objects in RSpec

account.rb

class Account
  attr_writer :logger, :username, :password

  def logger logger
    @logger ||= logger
  end

  def login
    # do authentication stuff...
    begin
      @logger.log('Invalid login')
    rescue
      # alternative logging
    end
  end

end

account_logger_collaboration_spec.rb

describe Account do

  describe "logging account activity" do

    context "when an invalid login attempt is made" do

      it "logs the failed attempt" do
        logger = double('Logger')
        logger.should_receive(:log).with('Invalid login')

        account = Account.new
        account.logger = logger

        account.username = 'invalid'
        account.password = 'invalid'

        account.login
      end

    end

    context "when its logger encounters a problem" do

      it "handles any errors raised" do
        logger = double('Logger')
        logger.stub(:log).and_raise "Logging unavailable"

        account = Account.new
        account.logger = logger

        account.username = 'irrelevant'
        account.password = 'irrelevant'

        expect { account.login }.to_not raise_error
      end

    end

  end

end

These tests focus on the collaboration between the Account and Logger objects, from the perspective of the Account object. At the same time, we're defining an implicit contract between Account and Logger, which we should test separately.

The trick is to keep track of all the, as yet, unimplemented conditions of the contract between all collaborators as we design.

I find these kind of collaboration tests, involving test doubles, guide me towards a clearer separation of concerns and nicer interfaces.

What if RSpec could tell us whenever we use a test double without implementing and/or checking that the real object does what we expect?

Could the proposed Undefined method stub report help us here?