small shuffle of test helpers, also guard helpers

Guardfile

@@ -4,6 +4,7 @@
 guard :minitest do
   # with Minitest::Unit
   watch(%r{^test/(.*)\/?test_(.*)\.rb$})
+  watch(%r{^test/(.*/)?helper.rb$})     { |m| "test/#{m[1]}test_all.rb" }
   watch(%r{^lib/(.*/)?([^/]+)\.rb$})     { |m| "test/#{m[1]}test_#{m[2]}.rb" }
   watch(%r{^test/test_helper\.rb$})      { 'test' }