Move testing_ruby_repo into test helper

Merged: https://github.com/ruby/ruby/pull/5669

test/rubygems/helper.rb

@@ -1187,6 +1187,14 @@ Also, a list:
     RUBY_PLATFORM.match('mswin')
   end
 
+  ##
+  # Is this test being run on a ruby/ruby repository?
+  #
+
+  def testing_ruby_repo?
+    !ENV["GEM_COMMAND"].nil?
+  end
+
   ##
   # Returns the make command for the current platform. For versions of Ruby
   # built on MS Windows with VC++ or Borland it will return 'nmake'. On all

test/rubygems/test_require.rb

@@ -671,10 +671,6 @@ class TestGemRequire < Gem::TestCase
 
   private
 
-  def testing_ruby_repo?
-    !ENV["GEM_COMMAND"].nil?
-  end
-
   def util_install_extension_file(name)
     spec = quick_gem name
     util_build_gem spec