Making a Dynamic Navigation in your Rails 4 layout

_navbar.html.erb

<nav>
  <ul class="nav nav-pills">
    <%= content_tag :li, link_to("Portfolio", welcome_portfolio_path), class: display_active('welcome#portfolio') %>
    <%= content_tag :li, link_to("About", welcome_about_path), class: display_active('welcome#about') %>
    <%= content_tag :li, link_to("Contact", welcome_contact_path), class: display_active('welcome#contact') %>
  </ul>
</nav>

application_helper.rb

module ApplicationHelper

  def controller_action_name
    "#{controller_name}##{action_name}"
  end

  def display_active controller_action
    controller_action == controller_action_name ? "active" : ""
  end

end

application_helper_spec.rb

# helper is an instance of ActionView::Base configured with the
# ApplicationHelper and all of Rails' built-in helpers

require "spec_helper"

describe ApplicationHelper do

  context '#controller_action_name' do
    it "calls #action_name" do
      helper.should_receive(:action_name)
      helper.controller_action_name
    end

    it 'calls #controller_name' do
      helper.should_receive(:controller_name)
      helper.controller_action_name
    end

    it 'returns a concatination of #controller_name and #action_name' do
      helper.stub(:controller_name).and_return('welcome')
      helper.stub(:action_name).and_return('about')
      helper.controller_action_name.should eq('welcome#about')
    end
  end

  context "#display_active" do
    it "returns 'active' if the current controller action equals the argument" do
      helper.stub(:controller_action_name).and_return('welcome#about')
      expect(helper.display_active('welcome#about')).to match /active/
    end

    it "returns '' if the current controller action does not equal the argument" do
      helper.stub(:controller_action_name).and_return('welcome#about')
      helper.display_active('welcome#contact').should eq('')
    end
  end

end