diff --git a/test/ruby/envutil.rb b/test/ruby/envutil.rb
index 972f63d056..1f74f2438d 100644
--- a/test/ruby/envutil.rb
+++ b/test/ruby/envutil.rb
@@ -128,81 +128,78 @@ module Test
 
       LANG_ENVS = %w"LANG LC_ALL LC_CTYPE"
 
-      def invoke_ruby_assertion(args, test_stdin="", test_stdout=nil, test_stderr=nil, test_status=true, message = nil, opt={})
-        in_c, in_p = IO.pipe
-        out_p, out_c = IO.pipe if test_stdout
-        err_p, err_c = IO.pipe if test_stderr
-        c = "C"
-        env = {}
-        LANG_ENVS.each {|lc| env[lc], ENV[lc] = ENV[lc], c}
-        opt = opt.dup
-        opt[:in] = in_c
-        opt[:out] = out_c if test_stdout
-        opt[:err] = err_c if test_stderr
-        pid = spawn(EnvUtil.rubybin, *args, opt)
-        in_c.close
-        out_c.close if test_stdout
-        err_c.close if test_stderr
-        in_p.write test_stdin
-        in_p.close
-        th_stdout = Thread.new { out_p.read } if test_stdout
-        th_stderr = Thread.new { err_p.read } if test_stderr
-        if (!test_stdout || th_stdout.join(10)) && (!test_stderr || th_stderr.join(10))
-          stdout = th_stdout.value if test_stdout
-          stderr = th_stderr.value if test_stderr
-        else
-          flunk("timeout")
-        end
-        out_p.close if test_stdout
-        err_p.close if test_stderr
-        Process.wait pid
-        status = $?
-        if block_given?
-          yield(test_stdout ? stdout.lines.map {|l| l.chomp } : nil, test_stderr ? stderr.lines.map {|l| l.chomp } : nil)
-        else
-          if test_stdout
-            if test_stdout.is_a?(Regexp)
-              assert_match(test_stdout, stdout, message)
-            else
-              assert_equal(test_stdout, stdout.lines.map {|l| l.chomp }, message)
-            end
-          end
-          if test_stderr
-            if test_stderr.is_a?(Regexp)
-              assert_match(test_stderr, stderr, message)
-            else
-              assert_equal(test_stderr, stderr.lines.map {|l| l.chomp }, message)
-            end
-          end
-        end
-        if test_status
-          assert(status.success?, "ruby exit stauts is not success: #{status.inspect}")
-        end
-        status
-      ensure
-        env.each_pair {|lc, v|
-          if v
-            ENV[lc] = v
+      def invoke_ruby(args, stdin_data="", capture_stdout=false, capture_stderr=false, opt={})
+        begin
+          in_c, in_p = IO.pipe
+          out_p, out_c = IO.pipe if capture_stdout
+          err_p, err_c = IO.pipe if capture_stderr
+          c = "C"
+          env = {}
+          LANG_ENVS.each {|lc| env[lc], ENV[lc] = ENV[lc], c}
+          opt = opt.dup
+          opt[:in] = in_c
+          opt[:out] = out_c if capture_stdout
+          opt[:err] = err_c if capture_stderr
+          pid = spawn(EnvUtil.rubybin, *args, opt)
+          in_c.close
+          out_c.close if capture_stdout
+          err_c.close if capture_stderr
+          in_p.write stdin_data
+          in_p.close
+          th_stdout = Thread.new { out_p.read } if capture_stdout
+          th_stderr = Thread.new { err_p.read } if capture_stderr
+          if (!capture_stdout || th_stdout.join(10)) && (!capture_stderr || th_stderr.join(10))
+            stdout = th_stdout.value if capture_stdout
+            stderr = th_stderr.value if capture_stderr
           else
-            ENV.delete(lc)
+            flunk("timeout")
           end
-        } if env
-        in_c.close if in_c && !in_c.closed?
-        in_p.close if in_p && !in_p.closed?
-        out_c.close if out_c && !out_c.closed?
-        out_p.close if out_p && !out_p.closed?
-        err_c.close if err_c && !err_c.closed?
-        err_p.close if err_p && !err_p.closed?
-        (th_stdout.kill; th_stdout.join) if th_stdout
-        (th_stderr.kill; th_stderr.join) if th_stderr
+          out_p.close if capture_stdout
+          err_p.close if capture_stderr
+          Process.wait pid
+          status = $?
+        ensure
+          env.each_pair {|lc, v|
+            if v
+              ENV[lc] = v
+            else
+              ENV.delete(lc)
+            end
+          } if env
+          in_c.close if in_c && !in_c.closed?
+          in_p.close if in_p && !in_p.closed?
+          out_c.close if out_c && !out_c.closed?
+          out_p.close if out_p && !out_p.closed?
+          err_c.close if err_c && !err_c.closed?
+          err_p.close if err_p && !err_p.closed?
+          (th_stdout.kill; th_stdout.join) if th_stdout
+          (th_stderr.kill; th_stderr.join) if th_stderr
+        end
+        return stdout, stderr, status
       end
 
-      def assert_in_out_err(args, test_stdin = "", test_stdout = [], test_stderr = [], message = nil, opt={}, &b)
-        invoke_ruby_assertion(args, test_stdin, test_stdout, test_stderr, false, message, opt, &b)
+      def assert_in_out_err(args, test_stdin = "", test_stdout = [], test_stderr = [], message = nil, opt={})
+        stdout, stderr, status = invoke_ruby(args, test_stdin, true, true, opt)
+        if block_given?
+          yield(stdout.lines.map {|l| l.chomp }, stderr.lines.map {|l| l.chomp })
+        else
+          if test_stdout.is_a?(Regexp)
+            assert_match(test_stdout, stdout, message)
+          else
+            assert_equal(test_stdout, stdout.lines.map {|l| l.chomp }, message)
+          end
+          if test_stderr.is_a?(Regexp)
+            assert_match(test_stderr, stderr, message)
+          else
+            assert_equal(test_stderr, stderr.lines.map {|l| l.chomp }, message)
+          end
+        end
       end
 
-      def assert_ruby_status(args, test_stdin = "", message = nil, opt={}, &b)
-        invoke_ruby_assertion(args, test_stdin, nil, nil, true, message, opt, &b)
+      def assert_ruby_status(args, test_stdin="", message=nil, opt={}, &b)
+        stdout, stderr, status = invoke_ruby(args, test_stdin, false, false, opt)
+        m = message ? "#{message} (#{status.inspect})" : "ruby exit stauts is not success: #{status.inspect}"
+        assert(status.success?, m)
       end
 
     end
diff --git a/test/ruby/test_dir_m17n.rb b/test/ruby/test_dir_m17n.rb
index 209189ab46..44a421874d 100644
--- a/test/ruby/test_dir_m17n.rb
+++ b/test/ruby/test_dir_m17n.rb
@@ -11,6 +11,93 @@ class TestDir_M17N < Test::Unit::TestCase
     }
   end
 
+  ## UTF-8 default_external, no default_internal
+
+  def test_filename_extutf8
+    with_tmpdir {|d|
+      assert_ruby_status(%w[-EUTF-8], <<-'EOS', nil, :chdir=>d)
+        filename = "\u3042"
+        File.open(filename, "w") {}
+        ents = Dir.entries(".")
+        exit ents.include?(filename)
+      EOS
+    }
+  end
+
+  def test_filename_extutf8_invalid
+    with_tmpdir {|d|
+      assert_ruby_status(%w[-EASCII-8BIT], <<-'EOS', nil, :chdir=>d)
+        filename = "\xff".force_encoding("ASCII-8BIT") # invalid byte sequence as UTF-8
+        File.open(filename, "w") {}
+        ents = Dir.entries(".")
+        exit ents.include?(filename)
+      EOS
+      assert_ruby_status(%w[-EUTF-8], <<-'EOS', nil, :chdir=>d)
+        filename = "\xff".force_encoding("UTF-8") # invalid byte sequence as UTF-8
+        File.open(filename, "w") {}
+        ents = Dir.entries(".")
+        exit ents.include?(filename)
+      EOS
+    }
+  end
+
+  ## UTF-8 default_external, EUC-JP default_internal
+
+  def test_filename_extutf8_inteucjp_representable
+    with_tmpdir {|d|
+      assert_ruby_status(%w[-EUTF-8], <<-'EOS', nil, :chdir=>d)
+        filename = "\u3042"
+        File.open(filename, "w") {}
+        ents = Dir.entries(".")
+        exit ents.include?(filename)
+      EOS
+      assert_ruby_status(%w[-EUTF-8:EUC-JP], <<-'EOS', nil, :chdir=>d)
+        filename = "\xA4\xA2".force_encoding("euc-jp")
+        ents = Dir.entries(".")
+        exit ents.include?(filename)
+      EOS
+      assert_ruby_status(%w[-EUTF-8:EUC-JP], <<-'EOS', nil, :chdir=>d)
+        filename = "\xA4\xA2".force_encoding("euc-jp")
+        begin
+          open(filename) {}
+          exit true
+        rescue Errno::ENOENT
+          exit false
+        end
+      EOS
+    }
+  end
+
+  def test_filename_extutf8_inteucjp_unrepresentable
+    with_tmpdir {|d|
+      assert_ruby_status(%w[-EUTF-8], <<-'EOS', nil, :chdir=>d)
+        filename1 = "\u2661" # WHITE HEART SUIT which is not representable in EUC-JP
+        filename2 = "\u3042" # HIRAGANA LETTER A which is representable in EUC-JP
+        File.open(filename1, "w") {}
+        File.open(filename2, "w") {}
+        ents = Dir.entries(".")
+        exit ents.include?(filename1) && ents.include?(filename2)
+      EOS
+      assert_ruby_status(%w[-EUTF-8:EUC-JP], <<-'EOS', nil, :chdir=>d)
+        filename1 = "\u2661" # WHITE HEART SUIT which is not representable in EUC-JP
+        filename2 = "\xA4\xA2".force_encoding("euc-jp") # HIRAGANA LETTER A in EUC-JP
+        ents = Dir.entries(".")
+        exit ents.include?(filename1) && ents.include?(filename2)
+      EOS
+      assert_ruby_status(%w[-EUTF-8:EUC-JP], <<-'EOS', nil, :chdir=>d)
+        filename1 = "\u2661" # WHITE HEART SUIT which is not representable in EUC-JP
+        filename2 = "\u3042" # HIRAGANA LETTER A which is representable in EUC-JP
+        filename3 = "\xA4\xA2".force_encoding("euc-jp") # HIRAGANA LETTER A in EUC-JP
+        s1 = File.stat(filename1) rescue nil
+        s2 = File.stat(filename2) rescue nil
+        s3 = File.stat(filename3) rescue nil
+        exit (s1 && s2 && s3) ? true : false
+      EOS
+    }
+  end
+
+  ## others
+
   def test_filename_bytes_euc_jp
     with_tmpdir {|d|
       assert_ruby_status(%w[-EEUC-JP], <<-'EOS', nil, :chdir=>d)
@@ -39,7 +126,7 @@ class TestDir_M17N < Test::Unit::TestCase
     }
   end
 
-  def test_filename_utf_8
+  def test_filename_utf8_raw_name
     with_tmpdir {|d|
       assert_ruby_status(%w[-EUTF-8], <<-'EOS', nil, :chdir=>d)
         filename = "\u3042".force_encoding("utf-8")
@@ -71,21 +158,5 @@ class TestDir_M17N < Test::Unit::TestCase
     }
   end
 
-  def test_filename_ext_utf_8_and_int_euc_jp
-    with_tmpdir {|d|
-      assert_ruby_status(%w[-EUTF-8], <<-'EOS', nil, :chdir=>d)
-        filename = "\u3042"
-        File.open(filename, "w") {}
-        ents = Dir.entries(".")
-        exit ents.include?(filename)
-      EOS
-      assert_ruby_status(%w[-EUTF-8:EUC-JP], <<-'EOS', nil, :chdir=>d)
-        filename = "\xA4\xA2".force_encoding("euc-jp")
-        ents = Dir.entries(".")
-        exit ents.include?(filename)
-      EOS
-    }
-  end
-
 end