diff --git a/spec/ruby/.rubocop_todo.yml b/spec/ruby/.rubocop_todo.yml
index a59e64bd58b6e0..3ebb23a8bb7f55 100644
--- a/spec/ruby/.rubocop_todo.yml
+++ b/spec/ruby/.rubocop_todo.yml
@@ -63,7 +63,6 @@ Lint/LiteralInInterpolation:
     - 'language/string_spec.rb'
     - 'language/symbol_spec.rb'
     - 'language/undef_spec.rb'
-    - 'library/net/ftp/connect_spec.rb'
 
 # Offense count: 8
 # Cop supports --auto-correct.
diff --git a/spec/ruby/core/encoding/replicate_spec.rb b/spec/ruby/core/encoding/replicate_spec.rb
index 498d03581ac6e5..68c285158d386c 100644
--- a/spec/ruby/core/encoding/replicate_spec.rb
+++ b/spec/ruby/core/encoding/replicate_spec.rb
@@ -73,6 +73,11 @@
         Encoding::US_ASCII.replicate('MY-US-ASCII')
       }.should complain(/warning: Encoding#replicate is deprecated and will be removed in Ruby 3.3; use the original encoding instead/)
     end
+
+    it "raises EncodingError if too many encodings" do
+      code = '1_000.times {|i| Encoding::US_ASCII.replicate("R_#{i}") }'
+      ruby_exe(code, args: "2>&1", exit_status: 1).should.include?('too many encoding (> 256) (EncodingError)')
+    end
   end
 
   ruby_version_is "3.3" do
diff --git a/spec/ruby/core/enumerable/fixtures/classes.rb b/spec/ruby/core/enumerable/fixtures/classes.rb
index fb4951c6e626a0..2701c6999c437a 100644
--- a/spec/ruby/core/enumerable/fixtures/classes.rb
+++ b/spec/ruby/core/enumerable/fixtures/classes.rb
@@ -342,4 +342,10 @@ def ===(*args)
       @block.call(*args)
     end
   end
+
+  # Set is a core class since Ruby 3.2
+  ruby_version_is '3.2' do
+    class SetSubclass < Set
+    end
+  end
 end # EnumerableSpecs utility classes
diff --git a/spec/ruby/core/enumerable/to_set_spec.rb b/spec/ruby/core/enumerable/to_set_spec.rb
new file mode 100644
index 00000000000000..c21a2772c4785d
--- /dev/null
+++ b/spec/ruby/core/enumerable/to_set_spec.rb
@@ -0,0 +1,29 @@
+require_relative '../../spec_helper'
+require_relative 'fixtures/classes'
+
+ruby_version_is "3.2" do
+  describe "Enumerable#to_set" do
+    it "returns a new Set created from self" do
+      [1, 2, 3].to_set.should == Set[1, 2, 3]
+      {a: 1, b: 2}.to_set.should == Set[[:b, 2], [:a, 1]]
+    end
+
+    it "passes down passed blocks" do
+      [1, 2, 3].to_set { |x| x * x }.should == Set[1, 4, 9]
+    end
+
+    it "instantiates an object of provided as the first argument set class" do
+      set = [1, 2, 3].to_set(EnumerableSpecs::SetSubclass)
+      set.should be_kind_of(EnumerableSpecs::SetSubclass)
+      set.to_a.sort.should == [1, 2, 3]
+    end
+
+    it "does not need explicit `require 'set'`" do
+      output = ruby_exe(<<~RUBY, options: '--disable-gems', args: '2>&1')
+        puts [1, 2, 3].to_set
+      RUBY
+
+      output.chomp.should == "#<Set: {1, 2, 3}>"
+    end
+  end
+end
diff --git a/spec/ruby/core/file/lutime_spec.rb b/spec/ruby/core/file/lutime_spec.rb
index 1f0625f61ebc2f..0f6df42ea37df5 100644
--- a/spec/ruby/core/file/lutime_spec.rb
+++ b/spec/ruby/core/file/lutime_spec.rb
@@ -1,7 +1,12 @@
 require_relative '../../spec_helper'
+require_relative 'shared/update_time'
 
-describe "File.lutime" do
-  platform_is_not :windows do
+platform_is_not :windows do
+  describe "File.lutime" do
+    it_behaves_like :update_time, :lutime
+  end
+
+  describe "File.lutime" do
     before :each do
       @atime = Time.utc(2000)
       @mtime = Time.utc(2001)
diff --git a/spec/ruby/core/file/shared/update_time.rb b/spec/ruby/core/file/shared/update_time.rb
new file mode 100644
index 00000000000000..9c063a8e935484
--- /dev/null
+++ b/spec/ruby/core/file/shared/update_time.rb
@@ -0,0 +1,105 @@
+describe :update_time, shared: true do
+  before :all do
+    @time_is_float = platform_is :windows
+  end
+
+  before :each do
+    @atime = Time.now
+    @mtime = Time.now
+    @file1 = tmp("specs_file_utime1")
+    @file2 = tmp("specs_file_utime2")
+    touch @file1
+    touch @file2
+  end
+
+  after :each do
+    rm_r @file1, @file2
+  end
+
+  it "sets the access and modification time of each file" do
+    File.send(@method, @atime, @mtime, @file1, @file2)
+
+    if @time_is_float
+      File.atime(@file1).should be_close(@atime, 0.0001)
+      File.mtime(@file1).should be_close(@mtime, 0.0001)
+      File.atime(@file2).should be_close(@atime, 0.0001)
+      File.mtime(@file2).should be_close(@mtime, 0.0001)
+    else
+      File.atime(@file1).to_i.should be_close(@atime.to_i, TIME_TOLERANCE)
+      File.mtime(@file1).to_i.should be_close(@mtime.to_i, TIME_TOLERANCE)
+      File.atime(@file2).to_i.should be_close(@atime.to_i, TIME_TOLERANCE)
+      File.mtime(@file2).to_i.should be_close(@mtime.to_i, TIME_TOLERANCE)
+    end
+  end
+
+  it "uses the current times if two nil values are passed" do
+    tn = Time.now
+    File.send(@method, nil, nil, @file1, @file2)
+
+    if @time_is_float
+      File.atime(@file1).should be_close(tn, 0.050)
+      File.mtime(@file1).should be_close(tn, 0.050)
+      File.atime(@file2).should be_close(tn, 0.050)
+      File.mtime(@file2).should be_close(tn, 0.050)
+    else
+      File.atime(@file1).to_i.should be_close(Time.now.to_i, TIME_TOLERANCE)
+      File.mtime(@file1).to_i.should be_close(Time.now.to_i, TIME_TOLERANCE)
+      File.atime(@file2).to_i.should be_close(Time.now.to_i, TIME_TOLERANCE)
+      File.mtime(@file2).to_i.should be_close(Time.now.to_i, TIME_TOLERANCE)
+    end
+  end
+
+  it "accepts an object that has a #to_path method" do
+    File.send(@method, @atime, @mtime, mock_to_path(@file1), mock_to_path(@file2))
+  end
+
+  it "accepts numeric atime and mtime arguments" do
+    if @time_is_float
+      File.send(@method, @atime.to_f, @mtime.to_f, @file1, @file2)
+
+      File.atime(@file1).should be_close(@atime, 0.0001)
+      File.mtime(@file1).should be_close(@mtime, 0.0001)
+      File.atime(@file2).should be_close(@atime, 0.0001)
+      File.mtime(@file2).should be_close(@mtime, 0.0001)
+    else
+      File.send(@method, @atime.to_i, @mtime.to_i, @file1, @file2)
+
+      File.atime(@file1).to_i.should be_close(@atime.to_i, TIME_TOLERANCE)
+      File.mtime(@file1).to_i.should be_close(@mtime.to_i, TIME_TOLERANCE)
+      File.atime(@file2).to_i.should be_close(@atime.to_i, TIME_TOLERANCE)
+      File.mtime(@file2).to_i.should be_close(@mtime.to_i, TIME_TOLERANCE)
+    end
+  end
+
+  it "may set nanosecond precision" do
+    t = Time.utc(2007, 11, 1, 15, 25, 0, 123456.789r)
+    File.send(@method, t, t, @file1)
+
+    File.atime(@file1).nsec.should.between?(0, 123500000)
+    File.mtime(@file1).nsec.should.between?(0, 123500000)
+  end
+
+  it "returns the number of filenames in the arguments" do
+    File.send(@method, @atime.to_f, @mtime.to_f, @file1, @file2).should == 2
+  end
+
+  platform_is :linux do
+    platform_is wordsize: 64 do
+      it "allows Time instances in the far future to set mtime and atime (but some filesystems limit it up to 2446-05-10 or 2038-01-19 or 2486-07-02)" do
+        # https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout#Inode_Timestamps
+        # "Therefore, timestamps should not overflow until May 2446."
+        # https://lwn.net/Articles/804382/
+        # "On-disk timestamps hitting the y2038 limit..."
+        # The problem seems to be being improved, but currently it actually fails on XFS on RHEL8
+        # https://rubyci.org/logs/rubyci.s3.amazonaws.com/rhel8/ruby-master/log/20201112T123004Z.fail.html.gz
+        # Amazon Linux 2023 returns 2486-07-02 in this example
+        # http://rubyci.s3.amazonaws.com/amazon2023/ruby-master/log/20230322T063004Z.fail.html.gz
+        time = Time.at(1<<44)
+        File.send(@method, time, time, @file1)
+
+        [559444, 2486, 2446, 2038].should.include? File.atime(@file1).year
+        [559444, 2486, 2446, 2038].should.include? File.mtime(@file1).year
+      end
+    end
+  end
+end
diff --git a/spec/ruby/core/file/utime_spec.rb b/spec/ruby/core/file/utime_spec.rb
index 0b0e4f979c9356..d87626be509458 100644
--- a/spec/ruby/core/file/utime_spec.rb
+++ b/spec/ruby/core/file/utime_spec.rb
@@ -1,102 +1,6 @@
 require_relative '../../spec_helper'
+require_relative 'shared/update_time'
 
 describe "File.utime" do
-
-  before :all do
-    @time_is_float = platform_is :windows
-  end
-
-  before :each do
-    @atime = Time.now
-    @mtime = Time.now
-    @file1 = tmp("specs_file_utime1")
-    @file2 = tmp("specs_file_utime2")
-    touch @file1
-    touch @file2
-  end
-
-  after :each do
-    rm_r @file1, @file2
-  end
-
-  it "sets the access and modification time of each file" do
-    File.utime(@atime, @mtime, @file1, @file2)
-    if @time_is_float
-      File.atime(@file1).should be_close(@atime, 0.0001)
-      File.mtime(@file1).should be_close(@mtime, 0.0001)
-      File.atime(@file2).should be_close(@atime, 0.0001)
-      File.mtime(@file2).should be_close(@mtime, 0.0001)
-    else
-      File.atime(@file1).to_i.should be_close(@atime.to_i, TIME_TOLERANCE)
-      File.mtime(@file1).to_i.should be_close(@mtime.to_i, TIME_TOLERANCE)
-      File.atime(@file2).to_i.should be_close(@atime.to_i, TIME_TOLERANCE)
-      File.mtime(@file2).to_i.should be_close(@mtime.to_i, TIME_TOLERANCE)
-    end
-  end
-
-  it "uses the current times if two nil values are passed" do
-    tn = Time.now
-    File.utime(nil, nil, @file1, @file2)
-    if @time_is_float
-      File.atime(@file1).should be_close(tn, 0.050)
-      File.mtime(@file1).should be_close(tn, 0.050)
-      File.atime(@file2).should be_close(tn, 0.050)
-      File.mtime(@file2).should be_close(tn, 0.050)
-    else
-      File.atime(@file1).to_i.should be_close(Time.now.to_i, TIME_TOLERANCE)
-      File.mtime(@file1).to_i.should be_close(Time.now.to_i, TIME_TOLERANCE)
-      File.atime(@file2).to_i.should be_close(Time.now.to_i, TIME_TOLERANCE)
-      File.mtime(@file2).to_i.should be_close(Time.now.to_i, TIME_TOLERANCE)
-    end
-  end
-
-  it "accepts an object that has a #to_path method" do
-    File.utime(@atime, @mtime, mock_to_path(@file1), mock_to_path(@file2))
-  end
-
-  it "accepts numeric atime and mtime arguments" do
-    if @time_is_float
-      File.utime(@atime.to_f, @mtime.to_f, @file1, @file2)
-      File.atime(@file1).should be_close(@atime, 0.0001)
-      File.mtime(@file1).should be_close(@mtime, 0.0001)
-      File.atime(@file2).should be_close(@atime, 0.0001)
-      File.mtime(@file2).should be_close(@mtime, 0.0001)
-    else
-      File.utime(@atime.to_i, @mtime.to_i, @file1, @file2)
-      File.atime(@file1).to_i.should be_close(@atime.to_i, TIME_TOLERANCE)
-      File.mtime(@file1).to_i.should be_close(@mtime.to_i, TIME_TOLERANCE)
-      File.atime(@file2).to_i.should be_close(@atime.to_i, TIME_TOLERANCE)
-      File.mtime(@file2).to_i.should be_close(@mtime.to_i, TIME_TOLERANCE)
-    end
-  end
-
-  it "may set nanosecond precision" do
-    t = Time.utc(2007, 11, 1, 15, 25, 0, 123456.789r)
-    File.utime(t, t, @file1)
-    File.atime(@file1).nsec.should.between?(0, 123500000)
-    File.mtime(@file1).nsec.should.between?(0, 123500000)
-  end
-
-  it "returns the number of filenames in the arguments" do
-    File.utime(@atime.to_f, @mtime.to_f, @file1, @file2).should == 2
-  end
-
-  platform_is :linux do
-    platform_is wordsize: 64 do
-      it "allows Time instances in the far future to set mtime and atime (but some filesystems limit it up to 2446-05-10 or 2038-01-19 or 2486-07-02)" do
-        # https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout#Inode_Timestamps
-        # "Therefore, timestamps should not overflow until May 2446."
-        # https://lwn.net/Articles/804382/
-        # "On-disk timestamps hitting the y2038 limit..."
-        # The problem seems to be being improved, but currently it actually fails on XFS on RHEL8
-        # https://rubyci.org/logs/rubyci.s3.amazonaws.com/rhel8/ruby-master/log/20201112T123004Z.fail.html.gz
-        # Amazon Linux 2023 returns 2486-07-02 in this example
-        # http://rubyci.s3.amazonaws.com/amazon2023/ruby-master/log/20230322T063004Z.fail.html.gz
-        time = Time.at(1<<44)
-        File.utime(time, time, @file1)
-        [559444, 2486, 2446, 2038].should.include? File.atime(@file1).year
-        [559444, 2486, 2446, 2038].should.include? File.mtime(@file1).year
-      end
-    end
-  end
+  it_behaves_like :update_time, :utime
 end
diff --git a/spec/ruby/core/filetest/exist_spec.rb b/spec/ruby/core/filetest/exist_spec.rb
index 4d14bea2311738..a95d3f91a18d96 100644
--- a/spec/ruby/core/filetest/exist_spec.rb
+++ b/spec/ruby/core/filetest/exist_spec.rb
@@ -4,3 +4,11 @@
 describe "FileTest.exist?" do
   it_behaves_like :file_exist, :exist?, FileTest
 end
+
+ruby_version_is "3.2" do
+  describe "FileTest.exists?" do
+    it "has been removed" do
+      FileTest.should_not.respond_to?(:exists?)
+    end
+  end
+end
diff --git a/spec/ruby/core/kernel/not_match_spec.rb b/spec/ruby/core/kernel/not_match_spec.rb
index 906f18df2c66e1..f8dd82fad86543 100644
--- a/spec/ruby/core/kernel/not_match_spec.rb
+++ b/spec/ruby/core/kernel/not_match_spec.rb
@@ -14,6 +14,20 @@ def !~(obj)
     (obj !~ :foo).should == false
   end
 
+  ruby_version_is ""..."3.2" do
+    it "returns true if self does not respond to #=~" do
+      suppress_warning do
+        (Object.new !~ :foo).should == true
+      end
+    end
+  end
+
+  ruby_version_is "3.2" do
+    it "raises NoMethodError if self does not respond to #=~" do
+      -> { Object.new !~ :foo }.should raise_error(NoMethodError)
+    end
+  end
+
   it 'can be overridden in subclasses' do
     obj = KernelSpecs::NotMatch.new
     (obj !~ :bar).should == :foo
diff --git a/spec/ruby/core/method/parameters_spec.rb b/spec/ruby/core/method/parameters_spec.rb
index 7d2b37fac75194..8495aef4d2d32d 100644
--- a/spec/ruby/core/method/parameters_spec.rb
+++ b/spec/ruby/core/method/parameters_spec.rb
@@ -22,6 +22,8 @@ def one_splat_one_block(*args, &block)
       local_is_not_parameter = {}
     end
 
+    def forward_parameters(...) end
+
     def underscore_parameters(_, _, _ = 1, *_, _:, _: 2, **_, &_); end
 
     define_method(:one_optional_defined_method) {|x = 1|}
@@ -267,6 +269,20 @@ def object.foo(&)
     end
   end
 
+  ruby_version_is ""..."3.1" do
+    it "returns [:rest, :*], [:block, :&] for forward parameters operator" do
+      m = MethodSpecs::Methods.new
+      m.method(:forward_parameters).parameters.should == [[:rest, :*], [:block, :&]]
+    end
+  end
+
+  ruby_version_is "3.1" do
+    it "returns [:rest, :*], [:keyrest, :**], [:block, :&] for forward parameters operator" do
+      m = MethodSpecs::Methods.new
+      m.method(:forward_parameters).parameters.should == [[:rest, :*], [:keyrest, :**], [:block, :&]]
+    end
+  end
+
   it "returns the args and block for a splat and block argument" do
     m = MethodSpecs::Methods.new
     m.method(:one_splat_one_block).parameters.should == [[:rest, :args], [:block, :block]]
diff --git a/spec/ruby/core/proc/parameters_spec.rb b/spec/ruby/core/proc/parameters_spec.rb
index 6c21784ab65d9d..972596d2ea8809 100644
--- a/spec/ruby/core/proc/parameters_spec.rb
+++ b/spec/ruby/core/proc/parameters_spec.rb
@@ -33,6 +33,16 @@
     it "regards named parameters in lambda as optional if lambda: false keyword used" do
       -> x { }.parameters(lambda: false).first.first.should == :opt
     end
+
+    it "regards named parameters in procs and lambdas as required if lambda keyword is truthy" do
+      proc {|x| }.parameters(lambda: 123).first.first.should == :req
+      -> x { }.parameters(lambda: 123).first.first.should == :req
+    end
+
+    it "ignores the lambda keyword if it is nil" do
+      proc {|x|}.parameters(lambda: nil).first.first.should == :opt
+      -> x { }.parameters(lambda: nil).first.first.should == :req
+    end
   end
 
   it "regards optional keyword parameters in procs as optional" do
@@ -160,4 +170,8 @@
       [:block, :_]
     ]
   end
+
+  it "returns :nokey for **nil parameter" do
+    proc { |**nil| }.parameters.should == [[:nokey]]
+  end
 end
diff --git a/spec/ruby/core/string/to_i_spec.rb b/spec/ruby/core/string/to_i_spec.rb
index e4fa89aab3e268..9931502baa2459 100644
--- a/spec/ruby/core/string/to_i_spec.rb
+++ b/spec/ruby/core/string/to_i_spec.rb
@@ -10,6 +10,18 @@
     "1_2_3asdf".to_i.should == 123
   end
 
+  it "ignores multiple non-consecutive underscoes when the first digit is 0" do
+    (2..16).each do |base|
+      "0_0_010".to_i(base).should == base;
+    end
+  end
+
+  it "bails out at the first double underscore if the first digit is 0" do
+    (2..16).each do |base|
+      "010__1".to_i(base).should == base;
+    end
+  end
+
   it "ignores leading whitespaces" do
     [ " 123", "     123", "\r\n\r\n123", "\t\t123",
       "\r\n\t\n123", " \t\n\r\t 123"].each do |str|
diff --git a/spec/ruby/library/net-ftp/connect_spec.rb b/spec/ruby/library/net-ftp/connect_spec.rb
index b5060bd1ca744c..4330d430b47c8d 100644
--- a/spec/ruby/library/net-ftp/connect_spec.rb
+++ b/spec/ruby/library/net-ftp/connect_spec.rb
@@ -29,7 +29,7 @@
   ruby_version_is ""..."3.1" do
     it "prints a small debug line when in debug mode" do
       @ftp.debug_mode = true
-      -> { @ftp.connect(@server.hostname, @server.server_port) }.should output(/#{"connect: "}#{@server.hostname}#{", "}#{@server.server_port}#{"\\nget: 220 Dummy FTP Server ready!"}/)
+      -> { @ftp.connect(@server.hostname, @server.server_port) }.should output(/connect: #{@server.hostname}, #{@server.server_port}\nget: 220 Dummy FTP Server ready!/)
       @ftp.debug_mode = false
     end
   end
diff --git a/spec/ruby/library/set/set_spec.rb b/spec/ruby/library/set/set_spec.rb
new file mode 100644
index 00000000000000..2a4edc6dfc63b4
--- /dev/null
+++ b/spec/ruby/library/set/set_spec.rb
@@ -0,0 +1,12 @@
+require_relative '../../spec_helper'
+
+describe 'Set' do
+  ruby_version_is '3.2' do
+    it 'is available without explicit requiring' do
+      output = ruby_exe(<<~RUBY, options: '--disable-gems', args: '2>&1')
+        puts Set.new([1, 2, 3])
+      RUBY
+      output.chomp.should == "#<Set: {1, 2, 3}>"
+    end
+  end
+end
diff --git a/spec/ruby/optional/capi/encoding_spec.rb b/spec/ruby/optional/capi/encoding_spec.rb
index 36437cc7b683b5..b0c38d75a93538 100644
--- a/spec/ruby/optional/capi/encoding_spec.rb
+++ b/spec/ruby/optional/capi/encoding_spec.rb
@@ -2,7 +2,7 @@
 require_relative 'spec_helper'
 require_relative 'fixtures/encoding'
 
-load_extension('encoding')
+extension_path = load_extension('encoding')
 
 describe :rb_enc_get_index, shared: true do
   it "returns the index of the encoding of a String" do
@@ -559,19 +559,19 @@
 
   describe "rb_ascii8bit_encindex" do
     it "returns an index for the ASCII-8BIT encoding" do
-      @s.rb_ascii8bit_encindex().should >= 0
+      @s.rb_ascii8bit_encindex().should == 0
     end
   end
 
   describe "rb_utf8_encindex" do
     it "returns an index for the UTF-8 encoding" do
-      @s.rb_utf8_encindex().should >= 0
+      @s.rb_utf8_encindex().should == 1
     end
   end
 
   describe "rb_usascii_encindex" do
     it "returns an index for the US-ASCII encoding" do
-      @s.rb_usascii_encindex().should >= 0
+      @s.rb_usascii_encindex().should == 2
     end
   end
 
@@ -721,4 +721,27 @@
       str.bytes.should == [0, 0x24]
     end
   end
+
+  describe "rb_define_dummy_encoding" do
+    it "defines the dummy encoding" do
+      @s.rb_define_dummy_encoding("FOO")
+      enc = Encoding.find("FOO")
+      enc.should.dummy?
+    end
+
+    it "returns the index of the dummy encoding" do
+      index = @s.rb_define_dummy_encoding("BAR")
+      index.should == Encoding.list.size - 1
+    end
+
+    ruby_version_is "3.2" do
+      it "raises EncodingError if too many encodings" do
+        code = <<-RUBY
+          require #{extension_path.dump}
+          1_000.times {|i| CApiEncodingSpecs.new.rb_define_dummy_encoding("R_\#{i}") }
+        RUBY
+        ruby_exe(code, args: "2>&1", exit_status: 1).should.include?('too many encoding (> 256) (EncodingError)')
+      end
+    end
+  end
 end
diff --git a/spec/ruby/optional/capi/ext/encoding_spec.c b/spec/ruby/optional/capi/ext/encoding_spec.c
index 3343848b542958..aa8662cfbd6426 100644
--- a/spec/ruby/optional/capi/ext/encoding_spec.c
+++ b/spec/ruby/optional/capi/ext/encoding_spec.c
@@ -320,6 +320,10 @@ static VALUE encoding_spec_rb_enc_left_char_head(VALUE self, VALUE str, VALUE of
   return LONG2NUM(result - ptr);
 }
 
+static VALUE encoding_spec_rb_define_dummy_encoding(VALUE self, VALUE name) {
+  return INT2NUM(rb_define_dummy_encoding(RSTRING_PTR(name)));
+}
+
 void Init_encoding_spec(void) {
   VALUE cls;
   native_rb_encoding_pointer = (rb_encoding**) malloc(sizeof(rb_encoding*));
@@ -379,6 +383,7 @@ void Init_encoding_spec(void) {
   rb_define_method(cls, "rb_uv_to_utf8", encoding_spec_rb_uv_to_utf8, 2);
   rb_define_method(cls, "ONIGENC_MBC_CASE_FOLD", encoding_spec_ONIGENC_MBC_CASE_FOLD, 1);
   rb_define_method(cls, "rb_enc_left_char_head", encoding_spec_rb_enc_left_char_head, 2);
+  rb_define_method(cls, "rb_define_dummy_encoding", encoding_spec_rb_define_dummy_encoding, 1);
 }
 
 #ifdef __cplusplus
diff --git a/spec/ruby/optional/capi/ext/string_spec.c b/spec/ruby/optional/capi/ext/string_spec.c
index c9c5277732ecbf..070a88759ba297 100644
--- a/spec/ruby/optional/capi/ext/string_spec.c
+++ b/spec/ruby/optional/capi/ext/string_spec.c
@@ -51,10 +51,6 @@ VALUE string_spec_rb_str_set_len_RSTRING_LEN(VALUE self, VALUE str, VALUE len) {
   return INT2FIX(RSTRING_LEN(str));
 }
 
-VALUE string_spec_rb_str_fstring(VALUE self, VALUE str) {
-  return rb_str_to_interned_str(str);
-}
-
 VALUE string_spec_rb_str_buf_new(VALUE self, VALUE len, VALUE str) {
   VALUE buf;
 
@@ -576,11 +572,19 @@ static VALUE string_spec_rb_str_unlocktmp(VALUE self, VALUE str) {
   return rb_str_unlocktmp(str);
 }
 
+static VALUE string_spec_rb_enc_interned_str_cstr(VALUE self, VALUE str, VALUE enc) {
+  rb_encoding *e = rb_to_encoding(enc);
+  return rb_enc_interned_str_cstr(RSTRING_PTR(str), e);
+}
+
+static VALUE string_spec_rb_str_to_interned_str(VALUE self, VALUE str) {
+  return rb_str_to_interned_str(str);
+}
+
 void Init_string_spec(void) {
   VALUE cls = rb_define_class("CApiStringSpecs", rb_cObject);
   rb_define_method(cls, "rb_cstr2inum", string_spec_rb_cstr2inum, 2);
   rb_define_method(cls, "rb_cstr_to_inum", string_spec_rb_cstr_to_inum, 3);
-  rb_define_method(cls, "rb_fstring", string_spec_rb_str_fstring, 1);
   rb_define_method(cls, "rb_str2inum", string_spec_rb_str2inum, 2);
   rb_define_method(cls, "rb_str_append", string_spec_rb_str_append, 2);
   rb_define_method(cls, "rb_str_buf_new", string_spec_rb_str_buf_new, 2);
@@ -677,6 +681,8 @@ void Init_string_spec(void) {
   rb_define_method(cls, "rb_str_catf", string_spec_rb_str_catf, 1);
   rb_define_method(cls, "rb_str_locktmp", string_spec_rb_str_locktmp, 1);
   rb_define_method(cls, "rb_str_unlocktmp", string_spec_rb_str_unlocktmp, 1);
+  rb_define_method(cls, "rb_enc_interned_str_cstr", string_spec_rb_enc_interned_str_cstr, 2);
+  rb_define_method(cls, "rb_str_to_interned_str", string_spec_rb_str_to_interned_str, 1);
 }
 
 #ifdef __cplusplus
diff --git a/spec/ruby/optional/capi/string_spec.rb b/spec/ruby/optional/capi/string_spec.rb
index 3a47fa9762fddc..d9c20cf1760ff9 100644
--- a/spec/ruby/optional/capi/string_spec.rb
+++ b/spec/ruby/optional/capi/string_spec.rb
@@ -498,25 +498,6 @@ def inspect
     end
   end
 
-  describe "rb_fstring" do
-    it 'returns self if the String is frozen' do
-      input  = 'foo'.freeze
-      output = @s.rb_fstring(input)
-
-      output.should equal(input)
-      output.should.frozen?
-    end
-
-    it 'returns a frozen copy if the String is not frozen' do
-      input  = 'foo'
-      output = @s.rb_fstring(input)
-
-      output.should.frozen?
-      output.should_not equal(input)
-      output.should == 'foo'
-    end
-  end
-
   describe "rb_str_subseq" do
     it "returns a byte-indexed substring" do
       str = "\x00\x01\x02\x03\x04".force_encoding("binary")
@@ -1227,4 +1208,59 @@ def inspect
       -> { @s.rb_str_unlocktmp("test") }.should raise_error(RuntimeError, 'temporal unlocking already unlocked string')
     end
   end
+
+  describe "rb_enc_interned_str_cstr" do
+    it "returns a frozen string" do
+      str = "hello"
+      val = @s.rb_enc_interned_str_cstr(str, Encoding::US_ASCII)
+
+      val.should.is_a?(String)
+      val.encoding.should == Encoding::US_ASCII
+      val.should.frozen?
+    end
+
+    it "returns the same frozen string" do
+      str = "hello"
+      result1 = @s.rb_enc_interned_str_cstr(str, Encoding::US_ASCII)
+      result2 = @s.rb_enc_interned_str_cstr(str, Encoding::US_ASCII)
+      result1.should.equal?(result2)
+    end
+
+    it "returns different frozen strings for different encodings" do
+      str = "hello"
+      result1 = @s.rb_enc_interned_str_cstr(str, Encoding::US_ASCII)
+      result2 = @s.rb_enc_interned_str_cstr(str, Encoding::UTF_8)
+      result1.should_not.equal?(result2)
+    end
+
+    it "returns the same string as String#-@" do
+      @s.rb_enc_interned_str_cstr("hello", Encoding::UTF_8).should.equal?(-"hello")
+    end
+  end
+
+  describe "rb_str_to_interned_str" do
+    it "returns a frozen string" do
+      str = "hello"
+      result = @s.rb_str_to_interned_str(str)
+      result.should.is_a?(String)
+      result.should.frozen?
+    end
+
+    it "returns the same frozen string" do
+      str = "hello"
+      result1 = @s.rb_str_to_interned_str(str)
+      result2 = @s.rb_str_to_interned_str(str)
+      result1.should.equal?(result2)
+    end
+
+    it "returns different frozen strings for different encodings" do
+      result1 = @s.rb_str_to_interned_str("hello".force_encoding(Encoding::US_ASCII))
+      result2 = @s.rb_str_to_interned_str("hello".force_encoding(Encoding::UTF_8))
+      result1.should_not.equal?(result2)
+    end
+
+    it "returns the same string as String#-@" do
+      @s.rb_str_to_interned_str("hello").should.equal?(-"hello")
+    end
+  end
 end