undefined method `describe' for main:Object (NoMethodError)`

RSpecを始めてみようと思ってここの記事を参考にサンプルを書いてみたらエラーが出て少し困った。

➜  sandbox  bundle exec rspec     
/Users/yamagh/GoogleDrive/dev/ruby/sandbox/spec/hello_spec.rb:3:in `<top (required)>': undefined method `describe' for main:Object (NoMethodError)
from /Library/Ruby/Gems/2.0.0/gems/rspec-core-3.1.7/lib/rspec/core/configuration.rb:1105:in `load'
from /Library/Ruby/Gems/2.0.0/gems/rspec-core-3.1.7/lib/rspec/core/configuration.rb:1105:in `block in load_spec_files'
from /Library/Ruby/Gems/2.0.0/gems/rspec-core-3.1.7/lib/rspec/core/configuration.rb:1105:in `each'
from /Library/Ruby/Gems/2.0.0/gems/rspec-core-3.1.7/lib/rspec/core/configuration.rb:1105:in `load_spec_files'
from /Library/Ruby/Gems/2.0.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:96:in `setup'
from /Library/Ruby/Gems/2.0.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:84:in `run'
from /Library/Ruby/Gems/2.0.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:69:in `run'
from /Library/Ruby/Gems/2.0.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:37:in `invoke'
from /Library/Ruby/Gems/2.0.0/gems/rspec-core-3.1.7/exe/rspec:4:in `<top (required)>'
from /usr/bin/rspec:23:in `load'
from /usr/bin/rspec:23:in `<main>'

記事の通りやってるしなんでだろーと思ったけど、とりあえず解決方法が分かったのでメモ。

[spec/spec_helper.rb]

 # Limits the available syntax to the non-monkey patched syntax that is recommended.
 # For more details, see:
 #   - http://myronmars.to/n/dev-blog/2012/06/rspecs-new-expectation-syntax
 #   - http://teaisaweso.me/blog/2013/05/27/rspecs-new-message-expectation-syntax/
 #   - http://myronmars.to/n/dev-blog/2014/05/notable-changes-in-rspec-3#new__config_option_to_disable_rspeccore_monkey_patching
 config.disable_monkey_patching!


rspec --init で生成される spec/spec_helper.rb の56行目あたりにある config.disable_monkey_patching! をコメントにするとエラー解消。

➜  sandbox  bundle exec rspec
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}

Hello
  message return hello

Finished in 0.00165 seconds (files took 0.13068 seconds to load)
1 example, 0 failures

Top 1 slowest examples (0.00089 seconds, 54.3% of total time):
  Hello message return hello
      0.00089 seconds ./spec/hello_spec.rb:4

Randomized with seed 5838

エラーなく動くようになりましたとさ。
原因は気が向いたら調べてみるかも。