authentication_helper.rb

# spec/support/authentication_helper.rb

module AuthenticationHelper
  def sign_in_as(user)
    visit new_user_session_path

    fill_in "Email", with: user.email
    fill_in "Password", with: user.password
    click_button "Sign in"

    expect(page).to have_link('Sign out')
  end
end

example_spec.rb

require 'spec_helper'

feature "user edits their profile" do
  scenario "some awesome description" do
    user = FactoryGirl.create(:user)
    sign_in_as user
    
    # do stuff as a logged in user
  end
end

spec_helper.rb

# spec/spec_helper.rb

# ... omitted

RSpec.configure do |config|
  # ... omitted
  config.include AuthenticationHelper
end