Switch mailer examples on rails version.

Rails 5 changes the class name generated for mailers from looking like
`Thing` to looking like `ThingMailer`. Our cukes depend on this name,
and so break as is. Here, I've added two tags, `@pre_rails_5` and
`@post_rails_5`.

The modification to the rakefile changes how we execute cukes based on
the rails version, filtering to the correct cukes.

Author: Sam Phippen

Rakefile

@@ -17,7 +17,16 @@ RSpec::Core::RakeTask.new(:spec) do |t|
   t.rspec_opts = %w[--color]
 end
 
-Cucumber::Rake::Task.new(:cucumber)
+Cucumber::Rake::Task.new(:cucumber) do |t|
+  version = ENV.fetch("RAILS_VERSION", "~> 4.2.0")
+  cucumber_flag = "--tags ~@rails_post_5"
+  p version
+  if /(^| )5(\.|-)0/ === version || version == "master"
+    cucumber_flag = "--tags ~@rails_pre_5"
+  end
+
+  t.cucumber_opts = cucumber_flag
+end
 
 namespace :generate do
   desc "generate a fresh app with rspec installed"

features/mailer_specs/url_helpers.feature

@@ -3,6 +3,46 @@ Feature: URL helpers in mailer examples
   Mailer specs are marked by `:type => :mailer` or if you have set
   `config.infer_spec_type_from_file_location!` by placing them in `spec/mailer`.
 
+  @rails_post_5
+  Scenario: using URL helpers with default options
+    Given a file named "config/initializers/mailer_defaults.rb" with:
+      """ruby
+      Rails.configuration.action_mailer.default_url_options = { :host => 'example.com' }
+      """
+    And a file named "spec/mailers/notifications_spec.rb" with:
+      """ruby
+      require 'rails_helper'
+
+      RSpec.describe NotificationsMailer, :type => :mailer do
+        it 'should have access to URL helpers' do
+          expect { gadgets_url }.not_to raise_error
+        end
+      end
+      """
+    When I run `rspec spec`
+    Then the examples should all pass
+
+  @rails_post_5
+  Scenario: using URL helpers without default options
+    Given a file named "config/initializers/mailer_defaults.rb" with:
+      """ruby
+      # no default options
+      """
+    And a file named "spec/mailers/notifications_spec.rb" with:
+      """ruby
+      require 'rails_helper'
+
+      RSpec.describe NotificationsMailer, :type => :mailer do
+        it 'should have access to URL helpers' do
+          expect { gadgets_url :host => 'example.com' }.not_to raise_error
+          expect { gadgets_url }.to raise_error
+        end
+      end
+      """
+    When I run `rspec spec`
+    Then the examples should all pass
+
+  @rails_pre_5
   Scenario: using URL helpers with default options
     Given a file named "config/initializers/mailer_defaults.rb" with:
       """ruby
@@ -21,6 +61,7 @@ Feature: URL helpers in mailer examples
     When I run `rspec spec`
     Then the examples should all pass
 
+  @rails_pre_5
   Scenario: using URL helpers without default options
     Given a file named "config/initializers/mailer_defaults.rb" with:
       """ruby