非ActiveRecord環境でRails 4.1にアップデートするとActiveRecord::ConnectionNotEstablishedが出る

## tl;dr
`spec_helper.rb`でモンキーパッチ読み込ませる

``` ruby
ENV["RAILS_ENV"] ||= 'test'
require File.expand_path("../../config/environment", __FILE__)

require_relative "../lib/monkey_patches/active_record"
require 'rspec/rails'
```

``` ruby
# rspec-railsがActiveRecordに繋ぎにいくので無理やり止める
ActiveRecord.module_eval do
  remove_const :TestFixtures
end
```

## 問題
Mongoidのアプリケーションを、Rails 4.1にアップデートしたらspecを走らせるときに `ActiveRecord::ConnectionNotEstablished` が出るようになった。

ActiveRecordを使ってないはずなのに、ActiveRecordで繋ごうとしていて明らかにおかしい。


```
     Failure/Error: Unable to find matching line from backtrace
     ActiveRecord::ConnectionNotEstablished:
       ActiveRecord::ConnectionNotEstablished
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.1.0/lib/active_record/connection_adapters/abstract/connection_pool.rb:541:in `retrieve_connection'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.1.0/lib/active_record/connection_handling.rb:113:in `retrieve_connection'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.1.0/lib/active_record/connection_handling.rb:87:in `connection'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.1.0/lib/active_record/fixtures.rb:499:in `create_fixtures'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.1.0/lib/active_record/fixtures.rb:985:in `load_fixtures'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.1.0/lib/active_record/fixtures.rb:958:in `setup_fixtures'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.1.0/lib/active_record/fixtures.rb:807:in `before_setup'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-rails-2.14.2/lib/rspec/rails/adapters.rb:68:in `block (2 levels) in <module:MinitestLifecycleAdapter>'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/extensions/instance_eval_with_args.rb:16:in `instance_exec'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/extensions/instance_eval_with_args.rb:16:in `instance_eval_with_args'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/example.rb:247:in `instance_eval_with_args'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/hooks.rb:106:in `block (2 levels) in run'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/hooks.rb:108:in `call'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/hooks.rb:108:in `run'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/hooks.rb:446:in `run_hook'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/example_group.rb:340:in `run_around_each_hooks'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/example.rb:256:in `with_around_each_hooks'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/example.rb:111:in `run'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/example_group.rb:390:in `block in run_examples'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/example_group.rb:386:in `map'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/example_group.rb:386:in `run_examples'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/example_group.rb:371:in `run'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/example_group.rb:372:in `block in run'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/example_group.rb:372:in `map'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/example_group.rb:372:in `run'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/command_line.rb:28:in `block (2 levels) in run'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/command_line.rb:28:in `map'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/command_line.rb:28:in `block in run'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/reporter.rb:58:in `report'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/command_line.rb:25:in `run'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/runner.rb:80:in `run'
     # /Users/zat/.rbenv/versions/2.1.0/lib/ruby/gems/2.1.0/gems/rspec-core-2.14.8/lib/rspec/core/runner.rb:17:in `block in autorun'

```

## 解決策

何かの拍子でActiveRecordが読み込まれると、specがtestのfixturesを作ろうとしてしまうので、ActiveRecordをいなかったことにする。

これを読み込ませればよい。

``` ruby
# rspec-railsがActiveRecordに繋ぎにいくので無理やり止める
ActiveRecord.module_eval do
  remove_const :TestFixtures
end
```