gem_path_test.rb

#! /usr/bin/env ruby

# -----------------------------------------------
# $ gem --version
# 1.3.5
# $ mkdir gemtest
# $ cd gemtest
# $ gem install -i . bluecloth
# $ gem_path_test.rb . bluecloth
# ERROR
# ERROR
# ERROR
# OK
# -----------------------------------------------

require 'rubygems'
Gem.path.unshift(ARGV[0])

def try_require
  begin
    require ARGV[1]
    puts "OK"
  rescue LoadError
    puts "ERROR"
  end
end

try_require # -> ERROR

Gem.refresh
try_require # -> ERROR

# Why need this line?
Gem.source_index.spec_dirs = Gem::SourceIndex.installed_spec_directories
try_require # -> ERROR

Gem.refresh
try_require # -> OK