Run `binding.irb` in cleaner environment and clean the history file

spec/ruby/core/binding/fixtures/irbrc

@@ -1 +0,0 @@
-# empty configuration

spec/ruby/core/binding/irb_spec.rb

@@ -1,18 +1,19 @@
 require_relative '../../spec_helper'
+require 'tmpdir'
 
 describe "Binding#irb" do
   it "creates an IRB session with the binding in scope" do
     irb_fixture = fixture __FILE__, "irb.rb"
-    irbrc_fixture = fixture __FILE__, "irbrc"
+    envs = %w[IRBRC HOME XDG_CONFIG_HOME].to_h {|e| [e, nil]}
 
-    out = IO.popen([{"IRBRC"=>irbrc_fixture}, *ruby_exe, irb_fixture], "r+") do |pipe|
-      pipe.puts "a ** 2"
-      pipe.puts "exit"
-      pipe.readlines.map(&:chomp)
+    out = Dir.mktmpdir do |dir|
+      IO.popen([envs, *ruby_exe, irb_fixture, chdir: dir], "r+") do |pipe|
+        pipe.puts "a ** 2"
+        pipe.puts "exit"
+        pipe.readlines.map(&:chomp)
+      end
     end
 
-    [out[-3..-1], ["a ** 2", "100", "exit"]].transpose.each do |actual, expected|
-      actual.should include(expected)
-    end
+    out.last(3).should == ["a ** 2", "100", "exit"]
   end
 end