rake test in sprockets-rails (commit 1608217, master at time of gist)

gistfile1.txt

Run options: 

# Running tests:

/Users/btaitelb/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/test/unit.rb:707:in `block in _prepare_run': undefined method `size' for #<ParallelEach:0x007fcebca02c00> (NoMethodError)
  from /Users/btaitelb/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/test/unit.rb:707:in `each'
	from /Users/btaitelb/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/test/unit.rb:707:in `inject'
	from /Users/btaitelb/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/test/unit.rb:707:in `_prepare_run'
	from /Users/btaitelb/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/test/unit.rb:648:in `_run_suites'
	from /Users/btaitelb/.rvm/gems/ruby-2.0.0-p0@sprockets-rails/gems/minitest-4.7.1/lib/minitest/unit.rb:861:in `_run_anything'
	from /Users/btaitelb/.rvm/gems/ruby-2.0.0-p0@sprockets-rails/gems/minitest-4.7.1/lib/minitest/unit.rb:1068:in `run_tests'
	from /Users/btaitelb/.rvm/gems/ruby-2.0.0-p0@sprockets-rails/gems/minitest-4.7.1/lib/minitest/unit.rb:1055:in `block in _run'
	from /Users/btaitelb/.rvm/gems/ruby-2.0.0-p0@sprockets-rails/gems/minitest-4.7.1/lib/minitest/unit.rb:1054:in `each'
	from /Users/btaitelb/.rvm/gems/ruby-2.0.0-p0@sprockets-rails/gems/minitest-4.7.1/lib/minitest/unit.rb:1054:in `_run'
	from /Users/btaitelb/.rvm/gems/ruby-2.0.0-p0@sprockets-rails/gems/minitest-4.7.1/lib/minitest/unit.rb:1042:in `run'
	from /Users/btaitelb/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/test/unit.rb:21:in `run'
	from /Users/btaitelb/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/test/unit.rb:774:in `run'
	from /Users/btaitelb/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/test/unit.rb:834:in `run'
	from /Users/btaitelb/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/test/unit.rb:838:in `run'
	from /Users/btaitelb/.rvm/rubies/ruby-2.0.0-p0/bin/testrb:7:in `<main>'

Works fine in ruby-1.9.3-p392, but seeing this error in ruby-2.0.0-p0