Extend RSpec DSL

I’m working on a project that need some complicated html snippets for test, which cannot be easily generated with factory. So I put these snippets into fixture files.

RSpec provides a very convenient DSL keyword let, which allow us to define something for test and cached it in the same test. And I want I could have some similar keyword for my html fixtures. To achieve this goal I decide to extend DSL.

So I created module which contains the new DSL I want to have:

DSL module

# spec/support/html_pages.rb
module HtmlPages
  def load_html(name)
    let name do
      file = Rails.root.join('spec/html_pages', "#{name}.html")
      Nokogiri::Html File.read(file)
    end
  end
end

Put this file into the path spec/support, by default, spec_helper.rb would require this file for you.
Then we should tell rspec to load the DSL into test cases.

Load DSL

RSpec.configure do |config|
	# ...
	config.extend HtmlPages
	# ...
end

By telling config to extend the module, our DSL will be loaded as the class methods of RSpec::Core::ExampleGroup, where let is being defined.

HINT: Rspec config has another way to extend DSL by calling config.include. Then the DSL methods will be injected into the test example group instance, then these methods can be used in the test cases. That’s how runtime DSLs like FactoryGirl work.