Testing a helper method with a minimalist approach

application_helper.rb

module ApplicationHelper
  def highlight_tag_if(condition, tag, &block)
    if condition
      content_tag tag, :class => 'hilite', &block
    else
      content_tag tag, &block
    end
  end
end

application_helper_spec.rb

require 'minitest/autorun'
require 'minitest/spec'
require_relative '../../app/helpers/application_helper'

class ApplicationHelperSpec < MiniTest::Spec
  describe "#highlight_tag_if" do
    describe "when the condition is true" do
      it "highlights the tag" do
	extend ApplicationHelper
	highlight_tag_if(true, :th) { }.must_match %r{^<th class='hilite'>.*</th>$}
      end
    end
  end
end