adding test for file open encoding bug reported at JRUBY-6572

file_open_test.rb

@@ -0,0 +1,20 @@
+require 'rubygems'
+require 'minitest/autorun'
+
+class FileOpenTest < MiniTest::Unit::TestCase
+
+  #works on both
+  def test_file_open_line_encoding_when_default_encoding_is_nil
+    Encoding.default_internal = nil
+    File.open('zh_cn-utf8.txt', 'rb') do |file|
+      assert_equal file.gets.encoding, Encoding::ASCII_8BIT
+    end
+  end
+
+  def test_file_open_line_encoding_when_default_encoding_is_utf8
+    Encoding.default_internal = 'utf-8'
+    File.open('zh_cn-utf8.txt', 'rb') do |file|
+      assert_equal file.gets.encoding, Encoding::ASCII_8BIT
+    end
+  end
+end

zh_cn-utf8.txt

@@ -0,0 +1 @@
+中