Use test_mode on Reline::History::Test for encoding

test/reline/test_history.rb

@@ -2,6 +2,10 @@ require_relative 'helper'
 require "reline/history"
 
 class Reline::History::Test < Reline::TestCase
+  def setup
+    Reline.send(:test_mode)
+  end
+
   def test_ancestors
     assert_equal(Reline::History.ancestors.include?(Array), true)
   end