Robby Russell: RSpec: It Should Behave Like

I was going through an older project of ours and cleaning up some specs and noticed how often we were doing the same thing in several places. When we started the project, we didn’t get the benefits of shared groups. Now that we have some time to go through and update some of our older specs, I’ve been trying to take advantage of the features currently available in RSpec. One feature that I haven’t seen a lot of mention of by people is shared groups, so I thought I’d take a few minutes to write up a quick intro to using it.

To pick some low-hanging fruit, let’s take an all-too-familiar method, which you might be familiar with… login_required. Sound familiar? Have you found yourself stubbing login_required over and over throughout your specs?

describe Admin::DohickiesController, 'index' do

  before( :each ) do
    controller.stub!( :login_required )
    Dohicky.should_receive( :paginate ).and_return( Array.new )
    get :index
  end

 ...
end

If you’re requiring that a user should be logged in when interacting with most of the application (as in the case of an administration section/namespace), you might want to consolidate some of your work into one shared specification group. The basic premise behind this is that you can write a typical describe block and load it into any other spec groups that you need. For example, in our case, we’ll need to stub login_required in several places. We can set this up in one shared group and reference it wherever necessary.

For example, here is what we’ll start off with.

describe "an admin user is signed in" do
  before( :each ) do
    controller.stub!( :login_required )
  end
end

describe Admin::DohickiesController, 'index' do
  ...

However, the new describe block isn’t accessible from the block at the bottom of the example… yet. To do this, we just need to pass the option: :shared => true as you’ll see in the following example.

describe "an admin user is signed in", :shared => true do
  before( :each ) do
    controller.stub!( :login_required )
  end
end

Great, now we can reference it by referring to it with: it_should_behave_like SharedGroupName. In our example above, this would look like:

describe "an admin user is signed in" do
  before( :each ) do
    controller.stub!( :login_required )
  end
end

describe Admin::DohickiesController, 'index' do
  it_should_behave_like "an admin user is signed in"

  before( :each ) do
    Dohicky.should_receive( :paginate ).and_return( Array.new )
    get :index
  end

 ...
end

describe Admin::DohickiesController, 'new' do
  it_should_behave_like "an admin user is signed in"

  before( :each ) do
    @dohicky = mock_model( Dohicky )
    Dohicky.should_receive( :new ).and_return( @dohicky )
    get :new
  end

  ...

That’s it! Pretty simple, eh? We can now reference this shared group in any describe blocks that we want to. A benefit to this approach is that we can make change the authentication system (say, we decide to switch it entirely and/or even just change method names, set any other prerequisites necessary when an admin is signed in), we’ll have a single place to change in our specs. (tip: you can put these in your spec_helper file)

You can learn more about it_should_behave_like and other helpful features on the RSpec documentation site.

If you have any suggestions on better ways of handling things like this, please follow up and share your solutions. I’m always looking to sharpen my tools. :-)

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