Merge pull request #610 from pvdb/fix_testhelper_require

refactor: only include `lib` in `$LOAD_PATH` if not included yet

Author: hsbt

test/helper.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
-$:.unshift File.expand_path("../../lib", __FILE__)
+
+lib = File.expand_path("../../lib", __FILE__)
+$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
 
 begin
   if ENV["COVERALLS"]