diff --git a/test/test_basic.rb b/test/test_basic.rb
index c6e2661..ba685fb 100644
--- a/test/test_basic.rb
+++ b/test/test_basic.rb
@@ -35,7 +35,7 @@ def test_open_without_block
 
   def test_open_with_block
     input = "#{EUCJ_STR}\n"*2
-    output = ""
+    output = String.new
     Iconv.open("Shift_JIS", "EUC-JP") do |cd|
       input.each_line do |s|
         output << cd.iconv(s)
diff --git a/test/test_option.rb b/test/test_option.rb
index 4eea8ce..3680997 100644
--- a/test/test_option.rb
+++ b/test/test_option.rb
@@ -1,13 +1,21 @@
 require File.expand_path("../utils.rb", __FILE__)
 
 class TestIconv::Option < TestIconv
-  def test_ignore_option
+  def setup
     begin
       iconv = Iconv.new('SHIFT_JIS', 'EUC-JP')
       iconv.transliterate?
     rescue NotImplementedError
-      return
+      omit "Iconv option is not implemented"
     end
+    @verbose, $VERBOSE = $VERBOSE, nil
+  end
+
+  def teardown
+    $VERBOSE = @verbose
+  end
+
+  def test_ignore_option
     iconv = Iconv.new('SHIFT_JIS', 'EUC-JP//ignore')
     str = iconv.iconv(EUCJ_STR)
     str << iconv.iconv(nil)
@@ -22,12 +30,6 @@ def test_ignore_option
   end
 
   def test_translit_option
-    begin
-      iconv = Iconv.new('SHIFT_JIS', 'EUC-JP')
-      iconv.transliterate?
-    rescue NotImplementedError
-      return
-    end
     iconv = Iconv.new('SHIFT_JIS', 'EUC-JP//ignore')
     str = iconv.iconv(EUCJ_STR)
     str << iconv.iconv(nil)
diff --git a/test/utils.rb b/test/utils.rb
index 88c64c6..8eb9ff8 100644
--- a/test/utils.rb
+++ b/test/utils.rb
@@ -4,7 +4,7 @@
 class TestIconv < ::Test::Unit::TestCase
   if defined?(::Encoding) and String.method_defined?(:force_encoding)
     def self.encode(str, enc)
-      str.force_encoding(enc)
+      str.dup.force_encoding(enc)
     end
   else
     def self.encode(str, enc)