Bump up minitest dependency and remove our own reinvented version of ParallelEach

activesupport/activesupport.gemspec

@@ -23,6 +23,6 @@
   s.add_dependency 'i18n',       '~> 0.6'
   s.add_dependency 'multi_json', '~> 1.3'
   s.add_dependency 'tzinfo',     '~> 0.3.33'
-  s.add_dependency 'minitest',   '~> 4.1'
+  s.add_dependency 'minitest',   '~> 4.2'
   s.add_dependency 'thread_safe','~> 0.1'
 end

activesupport/lib/active_support/testing/isolation.rb

 require 'rbconfig'
-begin
-  require 'minitest/parallel_each'
-rescue LoadError
-end
+require 'minitest/parallel_each'
 
 module ActiveSupport
   module Testing
@@ -48,39 +45,6 @@ def method_missing(name, *args)
     module Isolation
       require 'thread'
 
-      # Recent versions of MiniTest (such as the one shipped with Ruby 2.0) already define
-      # a ParallelEach class.
-      unless defined? ParallelEach
-        class ParallelEach
-          include Enumerable
-
-          # default to 2 cores
-          CORES = (ENV['TEST_CORES'] || 2).to_i
-
-          def initialize list
-            @list  = list
-            @queue = SizedQueue.new CORES
-          end
-
-          def grep pattern
-            self.class.new super
-          end
-
-          def each
-            threads = CORES.times.map {
-              Thread.new {
-                while job = @queue.pop
-                  yield job
-                end
-              }
-            }
-            @list.each { |i| @queue << i }
-            CORES.times { @queue << nil }
-            threads.each(&:join)
-          end
-        end
-      end
-
       def self.included(klass) #:nodoc:
         klass.extend(Module.new {
           def test_methods