Testing a ruby class without the required module files - ruby

Question

I'm working on a project in Ruby on Rails. We have a controller action that uses a module within a gem. This gem isn't finished yet and it isn't on the file system.
I was told to mock the module in order to test the controller. Is there a way to test this without the actual gem? Would mocking the 'require' calls work?
We are currently using Mocha for Mocking and Stubbing.
There is a way to mock the imports in python. Maybe there is a similar answer to mocking the requires in ruby.
How to mock an import
Or please let me know what would be the best way to handle this.
Update: The person who told me to mock it, suggested adding a stub file, but that would require adding test code to the controller and I don't want to do that.
Update 2: The controller uses methods declared in the Module.

Answer 1

If you are writing tests to mock the method calls, they would fail. For example,
controller.should_receive(:method_in_non_existent_module).with(args) #=> errors
In a correct Red->Green TDD scenario , this is alright because the next step would be to require the gem/file, include the module and add the method call in the controller and make the test pass. But you'll not be able to make the tests pass since you can't require the file because it doesn't exist yet.
May be the developer who asked you to mock the method meant to do so not in your tests, but in your actual code. For example, he's writing a gem 'dongle-jokes' which has a method that gets the most popular dongle joke from the most recent tech conference. He doesn't want the gem to be a blocker for you to finish the controller and the views so he asks you to use a dummy interface that spits out a dummy response.
Write the tests that fail
Add a file lib/dongle-jokes.rb
Add the following to that file.
module DongleJokes
def joke
"Dongle jokes aren't funny!"
end
end
Require the file and include the module, use the method in the controller.
The test should pass now. You can remove lib/dongle-jokes.rb when you start using the actual gem.

Answer 2

If you're working in Rails you shouldn't need to add a require to the controller anyway, as when you add the gem to your gemfile it will be required automatically on Rails startup.
What your colleague most likely meant was that you should stub the module itself. Are you using rspec for your tests? If so you should be able to use stub_const. Let's say the module is called Payments. You can then write test code like the following:
before do
stub_const("Payments", stub)
Payments.stub(process: "payments successful")
end