I was able to reproduce your issue. By the time the test example loads, the Sinatra Application has already loaded and is configured. It was only when I moved the application loading to after the environment is setup then did the intended configuration is loaded. An alternative is to set the ENV before the test is ran for example `RACK_ENV=produ…

itsadate.rb

require "rubygems"
require "icalendar"
require "date"
require "sinatra"
require 'erb'

configure :test do
  puts "Calling test"
end

configure :development do
  puts "Calling development"
end

configure :production do
  puts "Calling production"
end

get "/" do
  puts settings.environment

  erb :index
end

get "/event.ics" do
  cal = Icalendar::Calendar.new
  cal.event do
    dtstart       Date.new(2010, 02, 25)
    dtend         Date.new(2010, 02, 26)
    location    "Steven's House"
    organizer   "Steven Chau"
    summary     "Meeting with the man."
    description "Have a long lunch meeting and decide nothing..."
    klass       "PRIVATE"
  end

  content_type "text/calendar"
  cal.to_ical
end

itsadate_spec.rb

require 'sinatra'
require 'rack/test'

# setup test environment
set :environment, :test
set :run, false
set :raise_errors, true
set :logging, false

require File.join(File.dirname(__FILE__), 'itsadate.rb')  # Order matters

puts settings.environment

def app
  Sinatra::Application
end

RSpec.configure do |config|
  config.include Rack::Test::Methods
end

describe "Sinatra App" do

  it "should respond to GET" do
    get '/'

    last_response.should be_ok
    last_response.body.should match(/Make iCal Dates/)
  end

end