Как работает данный код из «RoR Tutorial» (Rspec)?

require 'spec_helper'
describe ApplicationHelper do
describe "full_title" do
it "should include the page title" do
expect(full_title("foo")).to match(/foo/)
end
it "should include the base title" do
expect(full_title("foo")).to match(/^Ruby on Rails Tutorial Sample App/)
end
it "should not include a bar for the home page" do
expect(full_title("")).not_to match(/\|/)
end
end
end

def full_title(page_title)
base_title = "Ruby on Rails Tutorial Sample App"
if page_title.empty?
base_title
else
"#{base_title} | #{page_title}"
end
end