diff --git a/activesupport/lib/active_support/multibyte.rb b/activesupport/lib/active_support/multibyte.rb
index 57e8e24bf4..5efe13c537 100644
--- a/activesupport/lib/active_support/multibyte.rb
+++ b/activesupport/lib/active_support/multibyte.rb
@@ -1,9 +1,5 @@
-# encoding: utf-8
-require 'active_support/core_ext/module/attribute_accessors'
-
 module ActiveSupport #:nodoc:
   module Multibyte
-    autoload :EncodingError, 'active_support/multibyte/exceptions'
     autoload :Chars, 'active_support/multibyte/chars'
     autoload :Unicode, 'active_support/multibyte/unicode'
 
@@ -21,24 +17,5 @@ module ActiveSupport #:nodoc:
     def self.proxy_class
       @proxy_class ||= ActiveSupport::Multibyte::Chars
     end
-
-    # Regular expressions that describe valid byte sequences for a character
-    VALID_CHARACTER = {
-      # Borrowed from the Kconv library by Shinji KONO - (also as seen on the W3C site)
-      'UTF-8' => /\A(?:
-                  [\x00-\x7f]                                         |
-                  [\xc2-\xdf] [\x80-\xbf]                             |
-                  \xe0        [\xa0-\xbf] [\x80-\xbf]                 |
-                  [\xe1-\xef] [\x80-\xbf] [\x80-\xbf]                 |
-                  \xf0        [\x90-\xbf] [\x80-\xbf] [\x80-\xbf]     |
-                  [\xf1-\xf3] [\x80-\xbf] [\x80-\xbf] [\x80-\xbf]     |
-                  \xf4        [\x80-\x8f] [\x80-\xbf] [\x80-\xbf])\z /xn,
-      # Quick check for valid Shift-JIS characters, disregards the odd-even pairing
-      'Shift_JIS' => /\A(?:
-                  [\x00-\x7e\xa1-\xdf]                                     |
-                  [\x81-\x9f\xe0-\xef] [\x40-\x7e\x80-\x9e\x9f-\xfc])\z /xn
-    }
   end
-end
-
-require 'active_support/multibyte/utils'
\ No newline at end of file
+end
\ No newline at end of file
diff --git a/activesupport/lib/active_support/multibyte/chars.rb b/activesupport/lib/active_support/multibyte/chars.rb
index dcc176e93f..99b974e4a7 100644
--- a/activesupport/lib/active_support/multibyte/chars.rb
+++ b/activesupport/lib/active_support/multibyte/chars.rb
@@ -1,6 +1,7 @@
 # encoding: utf-8
 require 'active_support/core_ext/string/access'
 require 'active_support/core_ext/string/behavior'
+require 'active_support/core_ext/module/delegation'
 
 module ActiveSupport #:nodoc:
   module Multibyte #:nodoc:
@@ -34,10 +35,13 @@ module ActiveSupport #:nodoc:
     #
     #   ActiveSupport::Multibyte.proxy_class = CharsForUTF32
     class Chars
+      include Comparable
       attr_reader :wrapped_string
       alias to_s wrapped_string
       alias to_str wrapped_string
 
+      delegate :<=>, :=~, :acts_like_string?, :to => :wrapped_string
+
       # Creates a new Chars instance by wrapping _string_.
       def initialize(string)
         @wrapped_string = string
@@ -47,8 +51,8 @@ module ActiveSupport #:nodoc:
       # Forward all undefined methods to the wrapped string.
       def method_missing(method, *args, &block)
         if method.to_s =~ /!$/
-          @wrapped_string.__send__(method, *args, &block)
-          self
+          result = @wrapped_string.__send__(method, *args, &block)
+          self if result
         else
           result = @wrapped_string.__send__(method, *args, &block)
           result.kind_of?(String) ? chars(result) : result
@@ -61,35 +65,9 @@ module ActiveSupport #:nodoc:
         super || @wrapped_string.respond_to?(method, include_private)
       end
 
-      # Enable more predictable duck-typing on String-like classes. See Object#acts_like?.
-      def acts_like_string?
-        true
-      end
-
       # Returns +true+ when the proxy class can handle the string. Returns +false+ otherwise.
       def self.consumes?(string)
-        # Unpack is a little bit faster than regular expressions.
-        string.unpack('U*')
-        true
-      rescue ArgumentError
-        false
-      end
-
-      include Comparable
-
-      # Returns -1, 0, or 1, depending on whether the Chars object is to be sorted before,
-      # equal or after the object on the right side of the operation. It accepts any object
-      # that implements +to_s+:
-      #
-      #   'é'.mb_chars <=> 'ü'.mb_chars # => -1
-      #
-      # See <tt>String#<=></tt> for more details.
-      def <=>(other)
-        @wrapped_string <=> other.to_s
-      end
-
-      def =~(other)
-        @wrapped_string =~ other
+        string.encoding == Encoding::UTF_8
       end
 
       # Works just like <tt>String#split</tt>, with the exception that the items in the resulting list are Chars
@@ -101,45 +79,10 @@ module ActiveSupport #:nodoc:
         @wrapped_string.split(*args).map { |i| i.mb_chars }
       end
 
-      # Like <tt>String#[]=</tt>, except instead of byte offsets you specify character offsets.
-      #
-      # Example:
-      #
-      #   s = "Müller"
-      #   s.mb_chars[2] = "e" # Replace character with offset 2
-      #   s
-      #   # => "Müeler"
-      #
-      #   s = "Müller"
-      #   s.mb_chars[1, 2] = "ö" # Replace 2 characters at character offset 1
-      #   s
-      #   # => "Möler"
-      def []=(*args)
-        replace_by = args.pop
-        # Indexed replace with regular expressions already works
-        if args.first.is_a?(Regexp)
-          @wrapped_string[*args] = replace_by
-        else
-          result = Unicode.u_unpack(@wrapped_string)
-          case args.first
-          when Fixnum
-            raise IndexError, "index #{args[0]} out of string" if args[0] >= result.length
-            min = args[0]
-            max = args[1].nil? ? min : (min + args[1] - 1)
-            range = Range.new(min, max)
-            replace_by = [replace_by].pack('U') if replace_by.is_a?(Fixnum)
-          when Range
-            raise RangeError, "#{args[0]} out of range" if args[0].min >= result.length
-            range = args[0]
-          else
-            needle = args[0].to_s
-            min = index(needle)
-            max = min + Unicode.u_unpack(needle).length - 1
-            range = Range.new(min, max)
-          end
-          result[range] = Unicode.u_unpack(replace_by)
-          @wrapped_string.replace(result.pack('U*'))
-        end
+      # Works like like <tt>String#slice!</tt>, but returns an instance of Chars, or nil if the string was not
+      # modified.
+      def slice!(*args)
+        chars(@wrapped_string.slice!(*args))
       end
 
       # Reverses all characters in the string.
@@ -147,37 +90,9 @@ module ActiveSupport #:nodoc:
       # Example:
       #   'Café'.mb_chars.reverse.to_s # => 'éfaC'
       def reverse
-        chars(Unicode.g_unpack(@wrapped_string).reverse.flatten.pack('U*'))
+        chars(Unicode.unpack_graphemes(@wrapped_string).reverse.flatten.pack('U*'))
       end
 
-      # Implements Unicode-aware slice with codepoints. Slicing on one point returns the codepoints for that
-      # character.
-      #
-      # Example:
-      #   'こんにちは'.mb_chars.slice(2..3).to_s # => "にち"
-      def slice(*args)
-        if args.size > 2
-          raise ArgumentError, "wrong number of arguments (#{args.size} for 1)" # Do as if we were native
-        elsif (args.size == 2 && !(args.first.is_a?(Numeric) || args.first.is_a?(Regexp)))
-          raise TypeError, "cannot convert #{args.first.class} into Integer" # Do as if we were native
-        elsif (args.size == 2 && !args[1].is_a?(Numeric))
-          raise TypeError, "cannot convert #{args[1].class} into Integer" # Do as if we were native
-        elsif args[0].kind_of? Range
-          cps = Unicode.u_unpack(@wrapped_string).slice(*args)
-          result = cps.nil? ? nil : cps.pack('U*')
-        elsif args[0].kind_of? Regexp
-          result = @wrapped_string.slice(*args)
-        elsif args.size == 1 && args[0].kind_of?(Numeric)
-          character = Unicode.u_unpack(@wrapped_string)[args[0]]
-          result = character && [character].pack('U')
-        else
-          cps = Unicode.u_unpack(@wrapped_string).slice(*args)
-          result = cps && cps.pack('U*')
-        end
-        result && chars(result)
-      end
-      alias_method :[], :slice
-
       # Limit the byte size of the string to a number of bytes without breaking characters. Usable
       # when the storage for a string is limited for some reason.
       #
@@ -192,7 +107,7 @@ module ActiveSupport #:nodoc:
       # Example:
       #   'Laurent, où sont les tests ?'.mb_chars.upcase.to_s # => "LAURENT, OÙ SONT LES TESTS ?"
       def upcase
-        chars(Unicode.apply_mapping @wrapped_string, :uppercase_mapping)
+        chars Unicode.upcase(@wrapped_string)
       end
 
       # Convert characters in the string to lowercase.
@@ -200,7 +115,7 @@ module ActiveSupport #:nodoc:
       # Example:
       #   'VĚDA A VÝZKUM'.mb_chars.downcase.to_s # => "věda a výzkum"
       def downcase
-        chars(Unicode.apply_mapping @wrapped_string, :lowercase_mapping)
+        chars Unicode.downcase(@wrapped_string)
       end
 
       # Converts the first character to uppercase and the remainder to lowercase.
@@ -217,7 +132,7 @@ module ActiveSupport #:nodoc:
       #   "ÉL QUE SE ENTERÓ".mb_chars.titleize    # => "Él Que Se Enteró"
       #   "日本語".mb_chars.titleize                 # => "日本語"
       def titleize
-        chars(downcase.to_s.gsub(/\b('?[\S])/u) { Unicode.apply_mapping $1, :uppercase_mapping })
+        chars(downcase.to_s.gsub(/\b('?[\S])/u) { Unicode.upcase($1)})
       end
       alias_method :titlecase, :titleize
 
@@ -237,7 +152,7 @@ module ActiveSupport #:nodoc:
       #   'é'.length                         # => 2
       #   'é'.mb_chars.decompose.to_s.length # => 3
       def decompose
-        chars(Unicode.decompose_codepoints(:canonical, Unicode.u_unpack(@wrapped_string)).pack('U*'))
+        chars(Unicode.decompose(:canonical, @wrapped_string.codepoints.to_a).pack('U*'))
       end
 
       # Performs composition on all the characters.
@@ -246,16 +161,16 @@ module ActiveSupport #:nodoc:
       #   'é'.length                       # => 3
       #   'é'.mb_chars.compose.to_s.length # => 2
       def compose
-        chars(Unicode.compose_codepoints(Unicode.u_unpack(@wrapped_string)).pack('U*'))
+        chars(Unicode.compose(@wrapped_string.codepoints.to_a).pack('U*'))
       end
 
       # Returns the number of grapheme clusters in the string.
       #
       # Example:
       #   'क्षि'.mb_chars.length   # => 4
-      #   'क्षि'.mb_chars.g_length # => 3
-      def g_length
-        Unicode.g_unpack(@wrapped_string).length
+      #   'क्षि'.mb_chars.grapheme_length # => 3
+      def grapheme_length
+        Unicode.unpack_graphemes(@wrapped_string).length
       end
 
       # Replaces all ISO-8859-1 or CP1252 characters by their UTF-8 equivalent resulting in a valid UTF-8 string.
@@ -265,14 +180,10 @@ module ActiveSupport #:nodoc:
         chars(Unicode.tidy_bytes(@wrapped_string, force))
       end
 
-       %w(capitalize downcase lstrip reverse rstrip slice strip tidy_bytes upcase).each do |method|
-        # Only define a corresponding bang method for methods defined in the proxy; On 1.9 the proxy will
-        # exclude lstrip!, rstrip! and strip! because they are already work as expected on multibyte strings.
-        if public_method_defined?(method)
-          define_method("#{method}!") do |*args|
-            @wrapped_string = send(args.nil? ? method : method, *args).to_s
-            self
-          end
+      %w(capitalize downcase reverse tidy_bytes upcase).each do |method|
+        define_method("#{method}!") do |*args|
+          @wrapped_string = send(method, *args).to_s
+          self
         end
       end
 
@@ -282,41 +193,14 @@ module ActiveSupport #:nodoc:
           return nil if byte_offset.nil?
           return 0   if @wrapped_string == ''
 
-          @wrapped_string = @wrapped_string.dup.force_encoding(Encoding::ASCII_8BIT)
-
           begin
-            @wrapped_string[0...byte_offset].unpack('U*').length
+            @wrapped_string.byteslice(0...byte_offset).unpack('U*').length
           rescue ArgumentError
             byte_offset -= 1
             retry
           end
         end
 
-        def justify(integer, way, padstr=' ') #:nodoc:
-          raise ArgumentError, "zero width padding" if padstr.length == 0
-          padsize = integer - size
-          padsize = padsize > 0 ? padsize : 0
-          case way
-          when :right
-            result = @wrapped_string.dup.insert(0, padding(padsize, padstr))
-          when :left
-            result = @wrapped_string.dup.insert(-1, padding(padsize, padstr))
-          when :center
-            lpad = padding((padsize / 2.0).floor, padstr)
-            rpad = padding((padsize / 2.0).ceil, padstr)
-            result = @wrapped_string.dup.insert(0, lpad).insert(-1, rpad)
-          end
-          chars(result)
-        end
-
-        def padding(padsize, padstr=' ') #:nodoc:
-          if padsize != 0
-            chars(padstr * ((padsize / Unicode.u_unpack(padstr).size) + 1)).slice(0, padsize)
-          else
-            ''
-          end
-        end
-
         def chars(string) #:nodoc:
           self.class.new(string)
         end
diff --git a/activesupport/lib/active_support/multibyte/exceptions.rb b/activesupport/lib/active_support/multibyte/exceptions.rb
deleted file mode 100644
index 62066e3c71..0000000000
--- a/activesupport/lib/active_support/multibyte/exceptions.rb
+++ /dev/null
@@ -1,8 +0,0 @@
-# encoding: utf-8
-
-module ActiveSupport #:nodoc:
-  module Multibyte #:nodoc:
-    # Raised when a problem with the encoding was found.
-    class EncodingError < StandardError; end
-  end
-end
\ No newline at end of file
diff --git a/activesupport/lib/active_support/multibyte/unicode.rb b/activesupport/lib/active_support/multibyte/unicode.rb
index 754ca9290b..94fb0a48aa 100644
--- a/activesupport/lib/active_support/multibyte/unicode.rb
+++ b/activesupport/lib/active_support/multibyte/unicode.rb
@@ -10,7 +10,7 @@ module ActiveSupport
       NORMALIZATION_FORMS = [:c, :kc, :d, :kd]
 
       # The Unicode version that is supported by the implementation
-      UNICODE_VERSION = '5.2.0'
+      UNICODE_VERSION = '6.0.0'
 
       # The default normalization used for operations that require normalization. It can be set to any of the
       # normalizations in NORMALIZATION_FORMS.
@@ -61,19 +61,6 @@ module ActiveSupport
       TRAILERS_PAT = /(#{codepoints_to_pattern(LEADERS_AND_TRAILERS)})+\Z/u
       LEADERS_PAT = /\A(#{codepoints_to_pattern(LEADERS_AND_TRAILERS)})+/u
 
-      # Unpack the string at codepoints boundaries. Raises an EncodingError when the encoding of the string isn't
-      # valid UTF-8.
-      #
-      # Example:
-      #   Unicode.u_unpack('Café') # => [67, 97, 102, 233]
-      def u_unpack(string)
-        begin
-          string.unpack 'U*'
-        rescue ArgumentError
-          raise EncodingError, 'malformed UTF-8 character'
-        end
-      end
-
       # Detect whether the codepoint is in a certain character class. Returns +true+ when it's in the specified
       # character class and +false+ otherwise. Valid character classes are: <tt>:cr</tt>, <tt>:lf</tt>, <tt>:l</tt>,
       # <tt>:v</tt>, <tt>:lv</tt>, <tt>:lvt</tt> and <tt>:t</tt>.
@@ -86,10 +73,10 @@ module ActiveSupport
       # Unpack the string at grapheme boundaries. Returns a list of character lists.
       #
       # Example:
-      #   Unicode.g_unpack('क्षि') # => [[2325, 2381], [2359], [2367]]
-      #   Unicode.g_unpack('Café') # => [[67], [97], [102], [233]]
-      def g_unpack(string)
-        codepoints = u_unpack(string)
+      #   Unicode.unpack_graphemes('क्षि') # => [[2325, 2381], [2359], [2367]]
+      #   Unicode.unpack_graphemes('Café') # => [[67], [97], [102], [233]]
+      def unpack_graphemes(string)
+        codepoints = string.codepoints.to_a
         unpacked = []
         pos = 0
         marker = 0
@@ -118,12 +105,12 @@ module ActiveSupport
         unpacked
       end
 
-      # Reverse operation of g_unpack.
+      # Reverse operation of unpack_graphemes.
       #
       # Example:
-      #   Unicode.g_pack(Unicode.g_unpack('क्षि')) # => 'क्षि'
-      def g_pack(unpacked)
-        (unpacked.flatten).pack('U*')
+      #   Unicode.pack_graphemes(Unicode.unpack_graphemes('क्षि')) # => 'क्षि'
+      def pack_graphemes(unpacked)
+        unpacked.flatten.pack('U*')
       end
 
       # Re-order codepoints so the string becomes canonical.
@@ -143,7 +130,7 @@ module ActiveSupport
       end
 
       # Decompose composed characters to the decomposed form.
-      def decompose_codepoints(type, codepoints)
+      def decompose(type, codepoints)
         codepoints.inject([]) do |decomposed, cp|
           # if it's a hangul syllable starter character
           if HANGUL_SBASE <= cp and cp < HANGUL_SLAST
@@ -156,7 +143,7 @@ module ActiveSupport
             decomposed.concat ncp
           # if the codepoint is decomposable in with the current decomposition type
           elsif (ncp = database.codepoints[cp].decomp_mapping) and (!database.codepoints[cp].decomp_type || type == :compatability)
-            decomposed.concat decompose_codepoints(type, ncp.dup)
+            decomposed.concat decompose(type, ncp.dup)
           else
             decomposed << cp
           end
@@ -164,7 +151,7 @@ module ActiveSupport
       end
 
       # Compose decomposed characters to the composed form.
-      def compose_codepoints(codepoints)
+      def compose(codepoints)
         pos = 0
         eoa = codepoints.length - 1
         starter_pos = 0
@@ -283,30 +270,27 @@ module ActiveSupport
       def normalize(string, form=nil)
         form ||= @default_normalization_form
         # See http://www.unicode.org/reports/tr15, Table 1
-        codepoints = u_unpack(string)
+        codepoints = string.codepoints.to_a
         case form
           when :d
-            reorder_characters(decompose_codepoints(:canonical, codepoints))
+            reorder_characters(decompose(:canonical, codepoints))
           when :c
-            compose_codepoints(reorder_characters(decompose_codepoints(:canonical, codepoints)))
+            compose(reorder_characters(decompose(:canonical, codepoints)))
           when :kd
-            reorder_characters(decompose_codepoints(:compatability, codepoints))
+            reorder_characters(decompose(:compatability, codepoints))
           when :kc
-            compose_codepoints(reorder_characters(decompose_codepoints(:compatability, codepoints)))
+            compose(reorder_characters(decompose(:compatability, codepoints)))
           else
             raise ArgumentError, "#{form} is not a valid normalization variant", caller
         end.pack('U*')
       end
 
-      def apply_mapping(string, mapping) #:nodoc:
-        u_unpack(string).map do |codepoint|
-          cp = database.codepoints[codepoint]
-          if cp and (ncp = cp.send(mapping)) and ncp > 0
-            ncp
-          else
-            codepoint
-          end
-        end.pack('U*')
+      def downcase(string)
+        apply_mapping string, :lowercase_mapping
+      end
+
+      def upcase(string)
+        apply_mapping string, :uppercase_mapping
       end
 
       # Holds data about a codepoint in the Unicode database
@@ -374,6 +358,17 @@ module ActiveSupport
 
       private
 
+      def apply_mapping(string, mapping) #:nodoc:
+        string.each_codepoint.map do |codepoint|
+          cp = database.codepoints[codepoint]
+          if cp and (ncp = cp.send(mapping)) and ncp > 0
+            ncp
+          else
+            codepoint
+          end
+        end.pack('U*')
+      end
+
       def tidy_byte(byte)
         if byte < 160
           [database.cp1252[byte] || byte].pack("U").unpack("C*")
diff --git a/activesupport/lib/active_support/multibyte/utils.rb b/activesupport/lib/active_support/multibyte/utils.rb
deleted file mode 100644
index bd6d4bad41..0000000000
--- a/activesupport/lib/active_support/multibyte/utils.rb
+++ /dev/null
@@ -1,27 +0,0 @@
-# encoding: utf-8
-
-module ActiveSupport #:nodoc:
-  module Multibyte #:nodoc:
-    # Returns a regular expression that matches valid characters in the current encoding
-    def self.valid_character
-      VALID_CHARACTER[Encoding.default_external.to_s]
-    end
-
-    # Verifies the encoding of a string
-    def self.verify(string)
-      string.valid_encoding?
-    end
-
-    # Verifies the encoding of the string and raises an exception when it's not valid
-    def self.verify!(string)
-      raise EncodingError.new("Found characters with invalid encoding") unless verify(string)
-    end
-
-    # Removes all invalid characters from the string.
-    #
-    # Note: this method is a no-op in Ruby 1.9
-    def self.clean(string)
-      string
-    end
-  end
-end
diff --git a/activesupport/lib/active_support/values/unicode_tables.dat b/activesupport/lib/active_support/values/unicode_tables.dat
index 4fe0268cca..7edc4663e8 100644
Binary files a/activesupport/lib/active_support/values/unicode_tables.dat and b/activesupport/lib/active_support/values/unicode_tables.dat differ
diff --git a/activesupport/test/multibyte_chars_test.rb b/activesupport/test/multibyte_chars_test.rb
index 20e56e2c81..e36bd22081 100644
--- a/activesupport/test/multibyte_chars_test.rb
+++ b/activesupport/test/multibyte_chars_test.rb
@@ -7,6 +7,7 @@ class String
   def __method_for_multibyte_testing_with_integer_result; 1; end
   def __method_for_multibyte_testing; 'result'; end
   def __method_for_multibyte_testing!; 'result'; end
+  def __method_for_multibyte_testing_that_returns_nil!; end
 end
 
 class MultibyteCharsTest < Test::Unit::TestCase
@@ -36,11 +37,15 @@ class MultibyteCharsTest < Test::Unit::TestCase
     assert_not_equal @chars.object_id, @chars.__method_for_multibyte_testing.object_id
   end
 
-  def test_forwarded_bang_method_calls_should_return_the_original_chars_instance
+  def test_forwarded_bang_method_calls_should_return_the_original_chars_instance_when_result_is_not_nil
     assert_kind_of @proxy_class, @chars.__method_for_multibyte_testing!
     assert_equal @chars.object_id, @chars.__method_for_multibyte_testing!.object_id
   end
 
+  def test_forwarded_bang_method_calls_should_return_nil_when_result_is_nil
+    assert_nil @chars.__method_for_multibyte_testing_that_returns_nil!
+  end
+
   def test_methods_are_forwarded_to_wrapped_string_for_byte_strings
     assert_equal BYTE_STRING.class, BYTE_STRING.mb_chars.class
   end
@@ -67,17 +72,6 @@ class MultibyteCharsTest < Test::Unit::TestCase
     assert !@proxy_class.consumes?(BYTE_STRING)
   end
 
-  def test_unpack_utf8_strings
-    assert_equal 4, ActiveSupport::Multibyte::Unicode.u_unpack(UNICODE_STRING).length
-    assert_equal 5, ActiveSupport::Multibyte::Unicode.u_unpack(ASCII_STRING).length
-  end
-
-  def test_unpack_raises_encoding_error_on_broken_strings
-    assert_raise(ActiveSupport::Multibyte::EncodingError) do
-      ActiveSupport::Multibyte::Unicode.u_unpack(BYTE_STRING)
-    end
-  end
-
   def test_concatenation_should_return_a_proxy_class_instance
     assert_equal ActiveSupport::Multibyte.proxy_class, ('a'.mb_chars + 'b').class
     assert_equal ActiveSupport::Multibyte.proxy_class, ('a'.mb_chars << 'b').class
@@ -112,15 +106,11 @@ class MultibyteCharsUTF8BehaviourTest < Test::Unit::TestCase
     end
   end
 
-  def test_indexed_insert_accepts_fixnums
-    @chars[2] = 32
-    assert_equal 'こに わ', @chars
-  end
-
-  %w{capitalize downcase lstrip reverse rstrip strip upcase}.each do |method|
+  %w{capitalize downcase lstrip reverse rstrip upcase}.each do |method|
     class_eval(<<-EOTESTS)
-      def test_#{method}_bang_should_return_self
-        assert_equal @chars.object_id, @chars.send("#{method}!").object_id
+      def test_#{method}_bang_should_return_self_when_modifying_wrapped_string
+        chars = ' él piDió Un bUen café '
+        assert_equal chars.object_id, chars.send("#{method}!").object_id
       end
 
       def test_#{method}_bang_should_change_wrapped_string
@@ -419,7 +409,7 @@ class MultibyteCharsUTF8BehaviourTest < Test::Unit::TestCase
   def test_slice_bang_removes_the_slice_from_the_receiver
     chars = 'úüù'.mb_chars
     chars.slice!(0,2)
-    assert_equal 'úü', chars
+    assert_equal 'ù', chars
   end
 
   def test_slice_should_throw_exceptions_on_invalid_arguments
@@ -506,7 +496,7 @@ class MultibyteCharsExtrasTest < Test::Unit::TestCase
 
   def test_limit_should_work_on_a_multibyte_string
     example = chars(UNICODE_STRING)
-    bytesize = UNICODE_STRING.respond_to?(:bytesize) ? UNICODE_STRING.bytesize : UNICODE_STRING.size
+    bytesize = UNICODE_STRING.bytesize
 
     assert_equal UNICODE_STRING, example.limit(bytesize)
     assert_equal '', example.limit(0)
@@ -605,7 +595,7 @@ class MultibyteCharsExtrasTest < Test::Unit::TestCase
       else
         str = input
       end
-      assert_equal expected_length, chars(str).g_length
+      assert_equal expected_length, chars(str).grapheme_length
     end
   end
 
diff --git a/activesupport/test/multibyte_utils_test.rb b/activesupport/test/multibyte_utils_test.rb
deleted file mode 100644
index f807492be0..0000000000
--- a/activesupport/test/multibyte_utils_test.rb
+++ /dev/null
@@ -1,93 +0,0 @@
-# encoding: utf-8
-
-require 'abstract_unit'
-require 'multibyte_test_helpers'
-
-class MultibyteUtilsTest < ActiveSupport::TestCase
-  include MultibyteTestHelpers
-
-  test "valid_character returns an expression for the current encoding" do
-    with_encoding('None') do
-      assert_nil ActiveSupport::Multibyte.valid_character
-    end
-    with_encoding('UTF8') do
-      assert_equal ActiveSupport::Multibyte::VALID_CHARACTER['UTF-8'], ActiveSupport::Multibyte.valid_character
-    end
-    with_encoding('SJIS') do
-      assert_equal ActiveSupport::Multibyte::VALID_CHARACTER['Shift_JIS'], ActiveSupport::Multibyte.valid_character
-    end
-  end
-
-  test "verify verifies ASCII strings are properly encoded" do
-    with_encoding('None') do
-      examples.each do |example|
-        assert ActiveSupport::Multibyte.verify(example)
-      end
-    end
-  end
-
-  test "verify verifies UTF-8 strings are properly encoded" do
-    with_encoding('UTF8') do
-      assert ActiveSupport::Multibyte.verify(example('valid UTF-8'))
-      assert !ActiveSupport::Multibyte.verify(example('invalid UTF-8'))
-    end
-  end
-
-  test "verify verifies Shift-JIS strings are properly encoded" do
-    with_encoding('SJIS') do
-      assert ActiveSupport::Multibyte.verify(example('valid Shift-JIS'))
-      assert !ActiveSupport::Multibyte.verify(example('invalid Shift-JIS'))
-    end
-  end
-
-  test "verify! raises an exception when it finds an invalid character" do
-    with_encoding('UTF8') do
-      assert_raises(ActiveSupport::Multibyte::EncodingError) do
-        ActiveSupport::Multibyte.verify!(example('invalid UTF-8'))
-      end
-    end
-  end
-
-  test "verify! doesn't raise an exception when the encoding is valid" do
-    with_encoding('UTF8') do
-      assert_nothing_raised do
-        ActiveSupport::Multibyte.verify!(example('valid UTF-8'))
-      end
-    end
-  end
-
-  test "clean is a no-op" do
-    with_encoding('UTF8') do
-      assert_equal example('invalid Shift-JIS'), ActiveSupport::Multibyte.clean(example('invalid Shift-JIS'))
-    end
-  end
-
-  private
-
-  STRINGS = {
-    'valid ASCII'       => [65, 83, 67, 73, 73].pack('C*'),
-    'invalid ASCII'     => [128].pack('C*'),
-    'valid UTF-8'       => [227, 129, 147, 227, 129, 171, 227, 129, 161, 227, 130, 143].pack('C*'),
-    'invalid UTF-8'     => [184, 158, 8, 136, 165].pack('C*'),
-    'valid Shift-JIS'   => [131, 122, 129, 91, 131, 128].pack('C*'),
-    'invalid Shift-JIS' => [184, 158, 8, 0, 255, 136, 165].pack('C*')
-  }
-
-  def example(key)
-    STRINGS[key].force_encoding(Encoding.default_external)
-  end
-
-  def examples
-    STRINGS.values.map { |s| s.force_encoding(Encoding.default_external) }
-  end
-
-  KCODE_TO_ENCODING = Hash.new(Encoding::BINARY).
-    update('UTF8' => Encoding::UTF_8, 'SJIS' => Encoding::Shift_JIS)
-
-  def with_encoding(enc)
-    before = Encoding.default_external
-    silence_warnings { Encoding.default_external = KCODE_TO_ENCODING[enc] }
-    yield
-    silence_warnings { Encoding.default_external = before }
-  end
-end