Encourage RACK_ENV=test environment variable setup instead of `set …

…:environment`

In order to avoid these kind of issues sinatra/sinatra#741

testing.markdown

@@ -38,12 +38,12 @@ makes a few helper methods and attributes available.
 The following is a simple example that ensures the hello world app functions
 properly:
 
+    ENV['RACK_ENV'] = 'test'
+
     require 'hello_world'
     require 'test/unit'
     require 'rack/test'
 
-    ENV['RACK_ENV'] = 'test'
-
     class HelloWorldTest < Test::Unit::TestCase
       include Rack::Test::Methods
 
@@ -69,13 +69,12 @@ For a variety of reasons you may not want to include `Rack::Test::Methods`
 into your own classes. `Rack::Test` supports this style of testing as well,
 here is the above example without using Mixin.
 
+    ENV['RACK_ENV'] = 'test'
 
     require 'hello_world'
     require 'test/unit'
     require 'rack/test'
 
-    set :environment, :test
-
     class HelloWorldTest < Test::Unit::TestCase
 
       def test_it_says_hello_world
@@ -183,12 +182,12 @@ removed in Sinatra `1.0`.
 Sinatra can be tested under plain RSpec. The `Rack::Test` module should be
 included within the `describe` block:
 
+    ENV['RACK_ENV'] = 'test'
+
     require 'hello_world'  # <-- your sinatra app
     require 'rspec'
     require 'rack/test'
 
-    set :environment, :test
-
     describe 'The HelloWorld App' do
       include Rack::Test::Methods
 
@@ -217,12 +216,12 @@ Make `Rack::Test` available to all spec contexts by including it via
 
 Testing with Bacon is similar to `test/unit` and RSpec:
 
+    ENV['RACK_ENV'] = 'test'
+
     require 'hello_world'  # <-- your sinatra app
     require 'bacon'
     require 'rack/test'
 
-    set :environment, :test
-
     describe 'The HelloWorld App' do
       extend Rack::Test::Methods
 
@@ -249,12 +248,12 @@ Make `Rack::Test` available to all spec contexts by including it in
 The `Rack::Test` module should be included within the context of the
 `describe` block:
 
+    ENV['RACK_ENV'] = 'test'
+
     require 'hello_world'  # <-- your sinatra app
     require 'test/spec'
     require 'rack/test'
 
-    set :environment, :test
-
     describe 'The HelloWorld App' do
       include Rack::Test::Methods
 
@@ -281,6 +280,8 @@ Make `Rack::Test` available to all spec contexts by including it in
 
 From `Webrat`'s wiki where you'll find more [examples][].
 
+    ENV['RACK_ENV'] = 'test'
+
     require 'hello_world'  # <-- your sinatra app
     require 'rack/test'
     require 'test/unit'
@@ -309,6 +310,8 @@ From `Webrat`'s wiki where you'll find more [examples][].
 `Capybara` will use `Rack::Test` by default. You can use another driver, like
 `Selenium`, by setting the default_driver.
 
+    ENV['RACK_ENV'] = 'test'
+
     require 'hello_world'  # <-- your sinatra app
     require 'capybara'
     require 'capybara/dsl'