'minitest/parallel_each' might not always be available
Isn't there a gem dependency on minitest? If so, it should always be available.
Yes, there is: https://github.com/rails/rails/blob/master/activesupport/activesupport.gemspec#L26
Rails is depending on 'minitest', '~> 4.1' and ParallelEach was introduced after 4.1 release seattlerb/minitest@bdbf38d
'minitest', '~> 4.1'
Or can I bump up the dependency so we can remove the Rails version of ParallelEach here? https://github.com/rails/rails/blob/eba172fb76ee46d9d801a5f3e56af7b777c9a13e/activesupport/lib/active_support/testing/isolation.rb#L51-L82
Yeah. ~> 4.2 should be good.