Use gem() to get a better error message.

thedarkone · thedarkone · commit 720e366ad135 · 2014-04-12T19:48:35.000+02:00
diff --git a/test/test_helper.rb b/test/test_helper.rb
@@ -1,5 +1,6 @@
 require 'thread'
 require 'rubygems'
+gem 'minitest', '>= 4'
 require 'minitest/autorun'
 
 if Minitest.const_defined?('Test')
