[ruby/irb] Test should not depend on user's irbrc file

(https://github.com/ruby/irb/pull/714)

https://github.com/ruby/irb/commit/02703c46f9

test/irb/helper.rb

@@ -110,6 +110,10 @@ module TestIRB
 
       yield
 
+      # Test should not depend on user's irbrc file
+      @envs["HOME"] ||= tmp_dir
+      @envs["XDG_CONFIG_HOME"] ||= tmp_dir
+
       PTY.spawn(@envs.merge("TERM" => "dumb"), *cmd) do |read, write, pid|
         Timeout.timeout(TIMEOUT_SEC) do
           while line = safe_gets(read)