Safe stubbing with bogus

In isolated tests in Ruby mocked interfaces may misalign with real ones while codebase grows. It can be avoided by using mocks that verify method definitions and fakes that keep those interfaces in sync.

Let's say we start with a repository class with a following store method:

def store(name)
end

And a controller that uses it:

def create(params)
  repository.store(params[:name])
end

We can test the interaction between them using rr:

it 'stores resources' do
  repository = stub
  mock(repository).store('Penguin') { nil }

  controller = Controller.new(repository)

  controller.create(name: 'Penguin')
end

After a while, we need to store the description as well:

def store(name, description)
end

However the controller test still passes while it is incorrect, because it doesn't know anything about repository interface. It can be easily fixed with Bogus by using fakes.

it 'saves images' do
  repository = fake(:repository)
  mock(repository).store('Penguin') { nil }

  controller = Controller.new(repository)

  controller.create(name: 'Penguin')
end

Now this tests fails with ArgumentError: tried to stub store(name, description) with 1 arguments which points us directly to the source of the problem.

Behind the scenes Bogus creates fakes by copying the public interface of repository, it adds mocking syntax that mimics the rr and verifies methods existence and arity.

You can find bogus on github and more details in documentation. Examples from this post are here.