subdomains.rb

# Support for Rspec / Capybara subdomain integration testing
# Make sure this file is required by spec_helper.rb
#  
# Sample subdomain test: 
# it "should test subdomain" do
#   switch_to_subdomain("mysubdomain")
#   visit root_path
# end

DEFAULT_HOST = "lvh.me"
DEFAULT_PORT = 9887

RSpec.configure do |config|
  Capybara.default_host = "http://#{DEFAULT_HOST}"
  Capybara.server_port = DEFAULT_PORT
  Capybara.app_host = "http://#{DEFAULT_HOST}:#{Capybara.server_port}"
end

def switch_to_subdomain(subdomain)
   Capybara.app_host = "http://#{subdomain}.#{DEFAULT_HOST}:#{DEFAULT_PORT}"
end

subdomains_spec.rb

# Sample spec file
require 'spec_helper'

describe "Subdomains", :js => true do

  it "should test subdomain" do
    switch_to_subdomain("mysubdomain")
    visit root_path
  end

end