18 files changed, 314 insertions, 364 deletions

diff --git a/spec/ruby/core/string/shared/byte_index_common.rb b/spec/ruby/core/string/shared/byte_index_common.rb
new file mode 100644
index 0000000000..3de1453f4f
--- /dev/null
+++ b/spec/ruby/core/string/shared/byte_index_common.rb
@@ -0,0 +1,63 @@
+# -*- encoding: utf-8 -*-
+require_relative '../../../spec_helper'
+
+describe :byte_index_common, shared: true do
+  describe "raises on type errors" do
+    it "raises a TypeError if passed nil" do
+      -> { "abc".send(@method, nil) }.should raise_error(TypeError, "no implicit conversion of nil into String")
+    end
+
+    it "raises a TypeError if passed a boolean" do
+      -> { "abc".send(@method, true) }.should raise_error(TypeError, "no implicit conversion of true into String")
+    end
+
+    it "raises a TypeError if passed a Symbol" do
+      not_supported_on :opal do
+        -> { "abc".send(@method, :a) }.should raise_error(TypeError, "no implicit conversion of Symbol into String")
+      end
+    end
+
+    it "raises a TypeError if passed a Symbol" do
+      obj = mock('x')
+      obj.should_not_receive(:to_int)
+      -> { "hello".send(@method, obj) }.should raise_error(TypeError, "no implicit conversion of MockObject into String")
+    end
+
+    it "raises a TypeError if passed an Integer" do
+      -> { "abc".send(@method, 97) }.should raise_error(TypeError, "no implicit conversion of Integer into String")
+    end
+  end
+
+  describe "with multibyte codepoints" do
+    it "raises an IndexError when byte offset lands in the middle of a multibyte character" do
+      -> { "わ".send(@method, "", 1) }.should raise_error(IndexError, "offset 1 does not land on character boundary")
+      -> { "わ".send(@method, "", 2) }.should raise_error(IndexError, "offset 2 does not land on character boundary")
+      -> { "わ".send(@method, "", -1) }.should raise_error(IndexError, "offset 2 does not land on character boundary")
+      -> { "わ".send(@method, "", -2) }.should raise_error(IndexError, "offset 1 does not land on character boundary")
+    end
+
+    it "raises an Encoding::CompatibilityError if the encodings are incompatible" do
+      re = Regexp.new "れ".encode(Encoding::EUC_JP)
+      -> do
+        "あれ".send(@method, re)
+      end.should raise_error(Encoding::CompatibilityError, "incompatible encoding regexp match (EUC-JP regexp with UTF-8 string)")
+    end
+  end
+
+  describe "with global variables" do
+    it "doesn't set $~ for non regex search" do
+      $~ = nil
+
+      'hello.'.send(@method, 'll')
+      $~.should == nil
+    end
+
+    it "sets $~ to MatchData of match and nil when there's none" do
+      'hello.'.send(@method, /.e./)
+      $~[0].should == 'hel'
+
+      'hello.'.send(@method, /not/)
+      $~.should == nil
+    end
+  end
+end
diff --git a/spec/ruby/core/string/shared/chars.rb b/spec/ruby/core/string/shared/chars.rb
index 1f045e4530..c730643cf4 100644
--- a/spec/ruby/core/string/shared/chars.rb
+++ b/spec/ruby/core/string/shared/chars.rb
@@ -21,12 +21,12 @@ describe :string_chars, shared: true do
   end
 
   it "returns characters in the same encoding as self" do
-    "&%".force_encoding('Shift_JIS').send(@method).to_a.all? {|c| c.encoding.name.should == 'Shift_JIS'}
+    "&%".dup.force_encoding('Shift_JIS').send(@method).to_a.all? {|c| c.encoding.name.should == 'Shift_JIS'}
     "&%".encode('BINARY').send(@method).to_a.all? {|c| c.encoding.should == Encoding::BINARY }
   end
 
   it "works with multibyte characters" do
-    s = "\u{8987}".force_encoding("UTF-8")
+    s = "\u{8987}".dup.force_encoding("UTF-8")
     s.bytesize.should == 3
     s.send(@method).to_a.should == [s]
   end
@@ -39,14 +39,14 @@ describe :string_chars, shared: true do
   end
 
   it "returns a different character if the String is transcoded" do
-    s = "\u{20AC}".force_encoding('UTF-8')
-    s.encode('UTF-8').send(@method).to_a.should == ["\u{20AC}".force_encoding('UTF-8')]
+    s = "\u{20AC}".dup.force_encoding('UTF-8')
+    s.encode('UTF-8').send(@method).to_a.should == ["\u{20AC}".dup.force_encoding('UTF-8')]
     s.encode('iso-8859-15').send(@method).to_a.should == [[0xA4].pack('C').force_encoding('iso-8859-15')]
-    s.encode('iso-8859-15').encode('UTF-8').send(@method).to_a.should == ["\u{20AC}".force_encoding('UTF-8')]
+    s.encode('iso-8859-15').encode('UTF-8').send(@method).to_a.should == ["\u{20AC}".dup.force_encoding('UTF-8')]
   end
 
   it "uses the String's encoding to determine what characters it contains" do
-    s = "\u{24B62}"
+    s = +"\u{24B62}"
 
     s.force_encoding('UTF-8').send(@method).to_a.should == [
       s.force_encoding('UTF-8')
@@ -63,18 +63,4 @@ describe :string_chars, shared: true do
       [0xA2].pack('C').force_encoding('SJIS')
     ]
   end
-
-  ruby_version_is ''...'2.7' do
-    it "taints resulting strings when self is tainted" do
-      str = "hello"
-
-      str.send(@method) do |x|
-        x.should_not.tainted?
-      end
-
-      str.dup.taint.send(@method) do |x|
-        x.should.tainted?
-      end
-    end
-  end
 end
diff --git a/spec/ruby/core/string/shared/codepoints.rb b/spec/ruby/core/string/shared/codepoints.rb
index 0b2e078e0a..f71263054a 100644
--- a/spec/ruby/core/string/shared/codepoints.rb
+++ b/spec/ruby/core/string/shared/codepoints.rb
@@ -7,7 +7,7 @@ describe :string_codepoints, shared: true do
   end
 
   it "raises an ArgumentError when self has an invalid encoding and a method is called on the returned Enumerator" do
-    s = "\xDF".force_encoding(Encoding::UTF_8)
+    s = "\xDF".dup.force_encoding(Encoding::UTF_8)
     s.valid_encoding?.should be_false
     -> { s.send(@method).to_a }.should raise_error(ArgumentError)
   end
@@ -21,7 +21,7 @@ describe :string_codepoints, shared: true do
   end
 
   it "raises an ArgumentError if self's encoding is invalid and a block is given" do
-    s = "\xDF".force_encoding(Encoding::UTF_8)
+    s = "\xDF".dup.force_encoding(Encoding::UTF_8)
     s.valid_encoding?.should be_false
     -> { s.send(@method) { } }.should raise_error(ArgumentError)
   end
@@ -49,7 +49,7 @@ describe :string_codepoints, shared: true do
 
   it "round-trips to the original String using Integer#chr" do
     s = "\u{13}\u{7711}\u{1010}"
-    s2 = ""
+    s2 = +""
     s.send(@method) {|n| s2 << n.chr(Encoding::UTF_8)}
     s.should == s2
   end
diff --git a/spec/ruby/core/string/shared/concat.rb b/spec/ruby/core/string/shared/concat.rb
index d6ffad7d4d..dded9a69e7 100644
--- a/spec/ruby/core/string/shared/concat.rb
+++ b/spec/ruby/core/string/shared/concat.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: false
 describe :string_concat, shared: true do
   it "concatenates the given argument to self and returns self" do
     str = 'hello '
@@ -5,18 +6,6 @@ describe :string_concat, shared: true do
     str.should == "hello world"
   end
 
-  it "converts the given argument to a String using to_str" do
-    obj = mock('world!')
-    obj.should_receive(:to_str).and_return("world!")
-    a = 'hello '.send(@method, obj)
-    a.should == 'hello world!'
-  end
-
-  it "raises a TypeError if the given argument can't be converted to a String" do
-    -> { 'hello '.send(@method, [])        }.should raise_error(TypeError)
-    -> { 'hello '.send(@method, mock('x')) }.should raise_error(TypeError)
-  end
-
   it "raises a FrozenError when self is frozen" do
     a = "hello"
     a.freeze
@@ -39,18 +28,6 @@ describe :string_concat, shared: true do
     str.should be_an_instance_of(StringSpecs::MyString)
   end
 
-  ruby_version_is ''...'2.7' do
-    it "taints self if other is tainted" do
-      "x".send(@method, "".taint).should.tainted?
-      "x".send(@method, "y".taint).should.tainted?
-    end
-
-    it "untrusts self if other is untrusted" do
-      "x".send(@method, "".untrust).should.untrusted?
-      "x".send(@method, "y".untrust).should.untrusted?
-    end
-  end
-
   describe "with Integer" do
     it "concatenates the argument interpreted as a codepoint" do
       b = "".send(@method, 33)
@@ -160,3 +137,23 @@ describe :string_concat_encoding, shared: true do
     end
   end
 end
+
+describe :string_concat_type_coercion, shared: true do
+  it "converts the given argument to a String using to_str" do
+    obj = mock('world!')
+    obj.should_receive(:to_str).and_return("world!")
+    a = 'hello '.send(@method, obj)
+    a.should == 'hello world!'
+  end
+
+  it "raises a TypeError if the given argument can't be converted to a String" do
+    -> { 'hello '.send(@method, [])        }.should raise_error(TypeError)
+    -> { 'hello '.send(@method, mock('x')) }.should raise_error(TypeError)
+  end
+
+  it "raises a NoMethodError if the given argument raises a NoMethodError during type coercion to a String" do
+    obj = mock('world!')
+    obj.should_receive(:to_str).and_raise(NoMethodError)
+    -> { 'hello '.send(@method, obj) }.should raise_error(NoMethodError)
+  end
+end
diff --git a/spec/ruby/core/string/shared/dedup.rb b/spec/ruby/core/string/shared/dedup.rb
new file mode 100644
index 0000000000..97b5df6ed1
--- /dev/null
+++ b/spec/ruby/core/string/shared/dedup.rb
@@ -0,0 +1,56 @@
+# frozen_string_literal: false
+describe :string_dedup, shared: true do
+  it 'returns self if the String is frozen' do
+    input  = 'foo'.freeze
+    output = input.send(@method)
+
+    output.should equal(input)
+    output.should.frozen?
+  end
+
+  it 'returns a frozen copy if the String is not frozen' do
+    input  = 'foo'
+    output = input.send(@method)
+
+    output.should.frozen?
+    output.should_not equal(input)
+    output.should == 'foo'
+  end
+
+  it "returns the same object for equal unfrozen strings" do
+    origin = "this is a string"
+    dynamic = %w(this is a string).join(' ')
+
+    origin.should_not equal(dynamic)
+    origin.send(@method).should equal(dynamic.send(@method))
+  end
+
+  it "returns the same object when it's called on the same String literal" do
+    "unfrozen string".send(@method).should equal("unfrozen string".send(@method))
+    "unfrozen string".send(@method).should_not equal("another unfrozen string".send(@method))
+  end
+
+  it "deduplicates frozen strings" do
+    dynamic = %w(this string is frozen).join(' ').freeze
+
+    dynamic.should_not equal("this string is frozen".freeze)
+
+    dynamic.send(@method).should equal("this string is frozen".freeze)
+    dynamic.send(@method).should equal("this string is frozen".send(@method).freeze)
+  end
+
+  it "does not deduplicate a frozen string when it has instance variables" do
+    dynamic = %w(this string is frozen).join(' ')
+    dynamic.instance_variable_set(:@a, 1)
+    dynamic.freeze
+
+    dynamic.send(@method).should_not equal("this string is frozen".freeze)
+    dynamic.send(@method).should_not equal("this string is frozen".send(@method).freeze)
+    dynamic.send(@method).should equal(dynamic)
+  end
+
+  it "interns the provided string if it is frozen" do
+    dynamic = "this string is unique and frozen #{rand}".freeze
+    dynamic.send(@method).should equal(dynamic)
+  end
+end
diff --git a/spec/ruby/core/string/shared/each_codepoint_without_block.rb b/spec/ruby/core/string/shared/each_codepoint_without_block.rb
index 92b7f76032..31b4c02c9c 100644
--- a/spec/ruby/core/string/shared/each_codepoint_without_block.rb
+++ b/spec/ruby/core/string/shared/each_codepoint_without_block.rb
@@ -6,7 +6,7 @@ describe :string_each_codepoint_without_block, shared: true do
     end
 
     it "returns an Enumerator even when self has an invalid encoding" do
-      s = "\xDF".force_encoding(Encoding::UTF_8)
+      s = "\xDF".dup.force_encoding(Encoding::UTF_8)
       s.valid_encoding?.should be_false
       s.send(@method).should be_an_instance_of(Enumerator)
     end
@@ -23,7 +23,7 @@ describe :string_each_codepoint_without_block, shared: true do
         end
 
         it "should return the size of the string even when the string has an invalid encoding" do
-          s = "\xDF".force_encoding(Encoding::UTF_8)
+          s = "\xDF".dup.force_encoding(Encoding::UTF_8)
           s.valid_encoding?.should be_false
           s.send(@method).size.should == 1
         end
diff --git a/spec/ruby/core/string/shared/each_line.rb b/spec/ruby/core/string/shared/each_line.rb
index f9c910596a..231a6d9d4f 100644
--- a/spec/ruby/core/string/shared/each_line.rb
+++ b/spec/ruby/core/string/shared/each_line.rb
@@ -40,14 +40,6 @@ describe :string_each_line, shared: true do
     b.should == ["foo\n", "🤡🤡🤡🤡🤡🤡🤡\n", "bar\n", "baz\n"]
   end
 
-  ruby_version_is ''...'2.7' do
-    it "taints substrings that are passed to the block if self is tainted" do
-      "one\ntwo\r\nthree".taint.send(@method) { |s| s.should.tainted? }
-
-      "x.y.".send(@method, ".".taint) { |s| s.should_not.tainted? }
-    end
-  end
-
   it "passes self as a whole to the block if the separator is nil" do
     a = []
     "one\ntwo\r\nthree".send(@method, nil) { |s| a << s }
@@ -93,20 +85,10 @@ describe :string_each_line, shared: true do
     end
   end
 
-  ruby_version_is ''...'3.0' do
-    it "yields subclass instances for subclasses" do
-      a = []
-      StringSpecs::MyString.new("hello\nworld").send(@method) { |s| a << s.class }
-      a.should == [StringSpecs::MyString, StringSpecs::MyString]
-    end
-  end
-
-  ruby_version_is '3.0' do
-    it "yields String instances for subclasses" do
-      a = []
-      StringSpecs::MyString.new("hello\nworld").send(@method) { |s| a << s.class }
-      a.should == [String, String]
-    end
+  it "yields String instances for subclasses" do
+    a = []
+    StringSpecs::MyString.new("hello\nworld").send(@method) { |s| a << s.class }
+    a.should == [String, String]
   end
 
   it "returns self" do
@@ -124,12 +106,18 @@ describe :string_each_line, shared: true do
   end
 
   it "does not care if the string is modified while substituting" do
-    str = "hello\nworld."
+    str = +"hello\nworld."
     out = []
     str.send(@method){|x| out << x; str[-1] = '!' }.should == "hello\nworld!"
     out.should == ["hello\n", "world."]
   end
 
+  it "returns Strings in the same encoding as self" do
+    "one\ntwo\r\nthree".encode("US-ASCII").send(@method) do |s|
+      s.encoding.should == Encoding::US_ASCII
+    end
+  end
+
   it "raises a TypeError when the separator can't be converted to a string" do
     -> { "hello world".send(@method, false) {}     }.should raise_error(TypeError)
     -> { "hello world".send(@method, mock('x')) {} }.should raise_error(TypeError)
diff --git a/spec/ruby/core/string/shared/encode.rb b/spec/ruby/core/string/shared/encode.rb
index a73de5b943..3776e0d709 100644
--- a/spec/ruby/core/string/shared/encode.rb
+++ b/spec/ruby/core/string/shared/encode.rb
@@ -1,4 +1,5 @@
 # -*- encoding: utf-8 -*-
+# frozen_string_literal: false
 describe :string_encode, shared: true do
   describe "when passed no options" do
     it "transcodes to Encoding.default_internal when set" do
diff --git a/spec/ruby/core/string/shared/eql.rb b/spec/ruby/core/string/shared/eql.rb
index 85b861f4f1..845b0a3e15 100644
--- a/spec/ruby/core/string/shared/eql.rb
+++ b/spec/ruby/core/string/shared/eql.rb
@@ -13,15 +13,15 @@ describe :string_eql_value, shared: true do
   end
 
   it "ignores encoding difference of compatible string" do
-    "hello".force_encoding("utf-8").send(@method, "hello".force_encoding("iso-8859-1")).should be_true
+    "hello".dup.force_encoding("utf-8").send(@method, "hello".dup.force_encoding("iso-8859-1")).should be_true
   end
 
   it "considers encoding difference of incompatible string" do
-    "\xff".force_encoding("utf-8").send(@method, "\xff".force_encoding("iso-8859-1")).should be_false
+    "\xff".dup.force_encoding("utf-8").send(@method, "\xff".dup.force_encoding("iso-8859-1")).should be_false
   end
 
   it "considers encoding compatibility" do
-    "hello".force_encoding("utf-8").send(@method, "hello".force_encoding("utf-32le")).should be_false
+    "abcd".dup.force_encoding("utf-8").send(@method, "abcd".dup.force_encoding("utf-32le")).should be_false
   end
 
   it "ignores subclass differences" do
@@ -31,4 +31,8 @@ describe :string_eql_value, shared: true do
     a.send(@method, b).should be_true
     b.send(@method, a).should be_true
   end
+
+  it "returns true when comparing 2 empty strings but one is not ASCII-compatible" do
+    "".send(@method, "".dup.force_encoding('iso-2022-jp')).should == true
+  end
 end
diff --git a/spec/ruby/core/string/shared/length.rb b/spec/ruby/core/string/shared/length.rb
index b9eae5170f..ae572ba755 100644
--- a/spec/ruby/core/string/shared/length.rb
+++ b/spec/ruby/core/string/shared/length.rb
@@ -12,13 +12,13 @@ describe :string_length, shared: true do
 
   it "returns the length of a string in different encodings" do
     utf8_str = 'こにちわ' * 100
-    utf8_str.size.should == 400
-    utf8_str.encode(Encoding::UTF_32BE).size.should == 400
-    utf8_str.encode(Encoding::SHIFT_JIS).size.should == 400
+    utf8_str.send(@method).should == 400
+    utf8_str.encode(Encoding::UTF_32BE).send(@method).should == 400
+    utf8_str.encode(Encoding::SHIFT_JIS).send(@method).should == 400
   end
 
   it "returns the length of the new self after encoding is changed" do
-    str = 'こにちわ'
+    str = +'こにちわ'
     str.send(@method)
 
     str.force_encoding('BINARY').send(@method).should == 12
@@ -32,8 +32,24 @@ describe :string_length, shared: true do
     concat.encoding.should == Encoding::UTF_8
     concat.bytesize.should == 4
 
-    concat.size.should == 2
+    concat.send(@method).should == 2
     concat.force_encoding(Encoding::ASCII_8BIT)
-    concat.size.should == 4
+    concat.send(@method).should == 4
+  end
+
+  it "adds 1 for every invalid byte in UTF-8" do
+    "\xF4\x90\x80\x80".send(@method).should == 4
+    "a\xF4\x90\x80\x80b".send(@method).should == 6
+    "é\xF4\x90\x80\x80è".send(@method).should == 6
+  end
+
+  it "adds 1 (and not 2) for a incomplete surrogate in UTF-16" do
+    "\x00\xd8".dup.force_encoding("UTF-16LE").send(@method).should == 1
+    "\xd8\x00".dup.force_encoding("UTF-16BE").send(@method).should == 1
+  end
+
+  it "adds 1 for a broken sequence in UTF-32" do
+    "\x04\x03\x02\x01".dup.force_encoding("UTF-32LE").send(@method).should == 1
+    "\x01\x02\x03\x04".dup.force_encoding("UTF-32BE").send(@method).should == 1
   end
 end
diff --git a/spec/ruby/core/string/shared/partition.rb b/spec/ruby/core/string/shared/partition.rb
new file mode 100644
index 0000000000..4cac149ce5
--- /dev/null
+++ b/spec/ruby/core/string/shared/partition.rb
@@ -0,0 +1,33 @@
+require_relative '../../../spec_helper'
+require_relative '../fixtures/classes'
+
+describe :string_partition, shared: true do
+  it "returns String instances when called on a subclass" do
+    StringSpecs::MyString.new("hello").send(@method, "l").each do |item|
+      item.should be_an_instance_of(String)
+    end
+
+    StringSpecs::MyString.new("hello").send(@method, "x").each do |item|
+      item.should be_an_instance_of(String)
+    end
+
+    StringSpecs::MyString.new("hello").send(@method, /l./).each do |item|
+      item.should be_an_instance_of(String)
+    end
+  end
+
+  it "returns before- and after- parts in the same encoding as self" do
+    strings = "hello".encode("US-ASCII").send(@method, "ello")
+    strings[0].encoding.should == Encoding::US_ASCII
+    strings[2].encoding.should == Encoding::US_ASCII
+
+    strings = "hello".encode("US-ASCII").send(@method, /ello/)
+    strings[0].encoding.should == Encoding::US_ASCII
+    strings[2].encoding.should == Encoding::US_ASCII
+  end
+
+  it "returns the matching part in the separator's encoding" do
+    strings = "hello".encode("US-ASCII").send(@method, "ello")
+    strings[1].encoding.should == Encoding::UTF_8
+  end
+end
diff --git a/spec/ruby/core/string/shared/replace.rb b/spec/ruby/core/string/shared/replace.rb
index 8dfac49f02..24dac0eb27 100644
--- a/spec/ruby/core/string/shared/replace.rb
+++ b/spec/ruby/core/string/shared/replace.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: false
 describe :string_replace, shared: true do
   it "returns self" do
     a = "a"
@@ -10,36 +11,6 @@ describe :string_replace, shared: true do
     a.should == "another string"
   end
 
-  ruby_version_is ''...'2.7' do
-    it "taints self if other is tainted" do
-      a = ""
-      b = "".taint
-      a.send(@method, b)
-      a.should.tainted?
-    end
-
-    it "does not untaint self if other is untainted" do
-      a = "".taint
-      b = ""
-      a.send(@method, b)
-      a.should.tainted?
-    end
-
-    it "untrusts self if other is untrusted" do
-      a = ""
-      b = "".untrust
-      a.send(@method, b)
-      a.should.untrusted?
-    end
-
-    it "does not trust self if other is trusted" do
-      a = "".untrust
-      b = ""
-      a.send(@method, b)
-      a.should.untrusted?
-    end
-  end
-
   it "replaces the encoding of self with that of other" do
     a = "".encode("UTF-16LE")
     b = "".encode("UTF-8")
diff --git a/spec/ruby/core/string/shared/slice.rb b/spec/ruby/core/string/shared/slice.rb
index 1db8fd6730..2f69b9ddce 100644
--- a/spec/ruby/core/string/shared/slice.rb
+++ b/spec/ruby/core/string/shared/slice.rb
@@ -80,23 +80,12 @@ describe :string_slice_index_length, shared: true do
     "hello there".send(@method, -3,2).should == "er"
   end
 
-  ruby_version_is ''...'2.7' do
-    it "always taints resulting strings when self is tainted" do
-      str = "hello world"
-      str.taint
-
-      str.send(@method, 0,0).should.tainted?
-      str.send(@method, 0,1).should.tainted?
-      str.send(@method, 2,1).should.tainted?
-    end
-  end
-
-  it "returns a string with the same encoding" do
+  it "returns a string with the same encoding as self" do
     s = "hello there"
     s.send(@method, 1, 9).encoding.should == s.encoding
 
-    a = "hello".force_encoding("binary")
-    b = " there".force_encoding("ISO-8859-1")
+    a = "hello".dup.force_encoding("binary")
+    b = " there".dup.force_encoding("ISO-8859-1")
     c = (a + b).force_encoding(Encoding::US_ASCII)
 
     c.send(@method, 0, 5).encoding.should == Encoding::US_ASCII
@@ -163,22 +152,11 @@ describe :string_slice_index_length, shared: true do
     -> { "hello".send(@method, 0, bignum_value) }.should raise_error(RangeError)
   end
 
-  ruby_version_is ''...'3.0' do
-    it "returns subclass instances" do
-      s = StringSpecs::MyString.new("hello")
-      s.send(@method, 0,0).should be_an_instance_of(StringSpecs::MyString)
-      s.send(@method, 0,4).should be_an_instance_of(StringSpecs::MyString)
-      s.send(@method, 1,4).should be_an_instance_of(StringSpecs::MyString)
-    end
-  end
-
-  ruby_version_is '3.0' do
-    it "returns String instances" do
-      s = StringSpecs::MyString.new("hello")
-      s.send(@method, 0,0).should be_an_instance_of(String)
-      s.send(@method, 0,4).should be_an_instance_of(String)
-      s.send(@method, 1,4).should be_an_instance_of(String)
-    end
+  it "returns String instances" do
+    s = StringSpecs::MyString.new("hello")
+    s.send(@method, 0,0).should be_an_instance_of(String)
+    s.send(@method, 0,4).should be_an_instance_of(String)
+    s.send(@method, 1,4).should be_an_instance_of(String)
   end
 
   it "handles repeated application" do
@@ -217,6 +195,10 @@ describe :string_slice_range, shared: true do
     "x".send(@method, 1..-1).should == ""
   end
 
+  it "returns a String in the same encoding as self" do
+    "hello there".encode("US-ASCII").send(@method, 1..1).encoding.should == Encoding::US_ASCII
+  end
+
   it "returns nil if the beginning of the range falls outside of self" do
     "hello there".send(@method, 12..-1).should == nil
     "hello there".send(@method, 20..25).should == nil
@@ -249,36 +231,11 @@ describe :string_slice_range, shared: true do
     "x".send(@method, 1...-1).should == ""
   end
 
-  ruby_version_is ''...'2.7' do
-    it "always taints resulting strings when self is tainted" do
-      str = "hello world"
-      str.taint
-
-      str.send(@method, 0..0).should.tainted?
-      str.send(@method, 0...0).should.tainted?
-      str.send(@method, 0..1).should.tainted?
-      str.send(@method, 0...1).should.tainted?
-      str.send(@method, 2..3).should.tainted?
-      str.send(@method, 2..0).should.tainted?
-    end
-  end
-
-  ruby_version_is ''...'3.0' do
-    it "returns subclass instances" do
-      s = StringSpecs::MyString.new("hello")
-      s.send(@method, 0...0).should be_an_instance_of(StringSpecs::MyString)
-      s.send(@method, 0..4).should be_an_instance_of(StringSpecs::MyString)
-      s.send(@method, 1..4).should be_an_instance_of(StringSpecs::MyString)
-    end
-  end
-
-  ruby_version_is '3.0' do
-    it "returns String instances" do
-      s = StringSpecs::MyString.new("hello")
-      s.send(@method, 0...0).should be_an_instance_of(String)
-      s.send(@method, 0..4).should be_an_instance_of(String)
-      s.send(@method, 1..4).should be_an_instance_of(String)
-    end
+  it "returns String instances" do
+    s = StringSpecs::MyString.new("hello")
+    s.send(@method, 0...0).should be_an_instance_of(String)
+    s.send(@method, 0..4).should be_an_instance_of(String)
+    s.send(@method, 1..4).should be_an_instance_of(String)
   end
 
   it "calls to_int on range arguments" do
@@ -334,14 +291,12 @@ describe :string_slice_range, shared: true do
     "hello there".send(@method, eval("(-4...)")).should == "here"
   end
 
-  ruby_version_is "2.7" do
-    it "works with beginless ranges" do
-      "hello there".send(@method, eval("(..5)")).should == "hello "
-      "hello there".send(@method, eval("(...5)")).should == "hello"
-      "hello there".send(@method, eval("(..-4)")).should == "hello th"
-      "hello there".send(@method, eval("(...-4)")).should == "hello t"
-      "hello there".send(@method, eval("(...nil)")).should == "hello there"
-    end
+  it "works with beginless ranges" do
+    "hello there".send(@method, (..5)).should == "hello "
+    "hello there".send(@method, (...5)).should == "hello"
+    "hello there".send(@method, (..-4)).should == "hello th"
+    "hello there".send(@method, (...-4)).should == "hello t"
+    "hello there".send(@method, (...nil)).should == "hello there"
   end
 end
 
@@ -355,43 +310,14 @@ describe :string_slice_regexp, shared: true do
     "hello there".send(@method, /xyz/).should == nil
   end
 
-  not_supported_on :opal do
-    ruby_version_is ''...'2.7' do
-      it "always taints resulting strings when self or regexp is tainted" do
-        strs = ["hello world"]
-        strs += strs.map { |s| s.dup.taint }
-
-        strs.each do |str|
-          str.send(@method, //).tainted?.should == str.tainted?
-          str.send(@method, /hello/).tainted?.should == str.tainted?
-
-          tainted_re = /./
-          tainted_re.taint
-
-          str.send(@method, tainted_re).should.tainted?
-        end
-      end
-
-      it "returns an untrusted string if the regexp is untrusted" do
-        "hello".send(@method, /./.untrust).untrusted?.should be_true
-      end
-    end
-  end
-
-  ruby_version_is ''...'3.0' do
-    it "returns subclass instances" do
-      s = StringSpecs::MyString.new("hello")
-      s.send(@method, //).should be_an_instance_of(StringSpecs::MyString)
-      s.send(@method, /../).should be_an_instance_of(StringSpecs::MyString)
-    end
+  it "returns a String in the same encoding as self" do
+    "hello there".encode("US-ASCII").send(@method, /[aeiou](.)\1/).encoding.should == Encoding::US_ASCII
   end
 
-  ruby_version_is '3.0' do
-    it "returns String instances" do
-      s = StringSpecs::MyString.new("hello")
-      s.send(@method, //).should be_an_instance_of(String)
-      s.send(@method, /../).should be_an_instance_of(String)
-    end
+  it "returns String instances" do
+    s = StringSpecs::MyString.new("hello")
+    s.send(@method, //).should be_an_instance_of(String)
+    s.send(@method, /../).should be_an_instance_of(String)
   end
 
   it "sets $~ to MatchData when there is a match and nil when there's none" do
@@ -418,44 +344,28 @@ describe :string_slice_regexp_index, shared: true do
     "har".send(@method, /(.)(.)(.)/, -3).should == "h"
   end
 
-  ruby_version_is ''...'2.7' do
-    it "always taints resulting strings when self or regexp is tainted" do
-      strs = ["hello world"]
-      strs += strs.map { |s| s.dup.taint }
-
-      strs.each do |str|
-        str.send(@method, //, 0).tainted?.should == str.tainted?
-        str.send(@method, /hello/, 0).tainted?.should == str.tainted?
-
-        str.send(@method, /(.)(.)(.)/, 0).tainted?.should == str.tainted?
-        str.send(@method, /(.)(.)(.)/, 1).tainted?.should == str.tainted?
-        str.send(@method, /(.)(.)(.)/, -1).tainted?.should == str.tainted?
-        str.send(@method, /(.)(.)(.)/, -2).tainted?.should == str.tainted?
-
-        tainted_re = /(.)(.)(.)/
-        tainted_re.taint
-
-        str.send(@method, tainted_re, 0).should.tainted?
-        str.send(@method, tainted_re, 1).should.tainted?
-        str.send(@method, tainted_re, -1).should.tainted?
-      end
-    end
-
-    not_supported_on :opal do
-      it "returns an untrusted string if the regexp is untrusted" do
-        "hello".send(@method, /(.)/.untrust, 1).untrusted?.should be_true
-      end
-    end
-  end
-
   it "returns nil if there is no match" do
     "hello there".send(@method, /(what?)/, 1).should == nil
   end
 
+  it "returns nil if the index is larger than the number of captures" do
+    "hello there".send(@method, /hello (.)/, 2).should == nil
+    # You can't refer to 0 using negative indices
+    "hello there".send(@method, /hello (.)/, -2).should == nil
+  end
+
   it "returns nil if there is no capture for the given index" do
     "hello there".send(@method, /[aeiou](.)\1/, 2).should == nil
-    # You can't refer to 0 using negative indices
-    "hello there".send(@method, /[aeiou](.)\1/, -2).should == nil
+  end
+
+  it "returns nil if the given capture group was not matched but still sets $~" do
+    "test".send(@method, /te(z)?/, 1).should == nil
+    $~[0].should == "te"
+    $~[1].should == nil
+  end
+
+  it "returns a String in the same encoding as self" do
+    "hello there".encode("US-ASCII").send(@method, /[aeiou](.)\1/, 0).encoding.should == Encoding::US_ASCII
   end
 
   it "calls to_int on the given index" do
@@ -476,20 +386,10 @@ describe :string_slice_regexp_index, shared: true do
     -> { "hello".send(@method, /(.)(.)(.)/, nil) }.should raise_error(TypeError)
   end
 
-  ruby_version_is ''...'3.0' do
-    it "returns subclass instances" do
-      s = StringSpecs::MyString.new("hello")
-      s.send(@method, /(.)(.)/, 0).should be_an_instance_of(StringSpecs::MyString)
-      s.send(@method, /(.)(.)/, 1).should be_an_instance_of(StringSpecs::MyString)
-    end
-  end
-
-  ruby_version_is '3.0' do
-    it "returns String instances" do
-      s = StringSpecs::MyString.new("hello")
-      s.send(@method, /(.)(.)/, 0).should be_an_instance_of(String)
-      s.send(@method, /(.)(.)/, 1).should be_an_instance_of(String)
-    end
+  it "returns String instances" do
+    s = StringSpecs::MyString.new("hello")
+    s.send(@method, /(.)(.)/, 0).should be_an_instance_of(String)
+    s.send(@method, /(.)(.)/, 1).should be_an_instance_of(String)
   end
 
   it "sets $~ to MatchData when there is a match and nil when there's none" do
@@ -510,21 +410,6 @@ describe :string_slice_string, shared: true do
     "hello there".send(@method, s).should == s
   end
 
-  ruby_version_is ''...'2.7' do
-    it "taints resulting strings when other is tainted" do
-      strs = ["", "hello world", "hello"]
-      strs += strs.map { |s| s.dup.taint }
-
-      strs.each do |str|
-        strs.each do |other|
-          r = str.send(@method, other)
-
-          r.tainted?.should == !r.nil? & other.tainted?
-        end
-      end
-    end
-  end
-
   it "doesn't set $~" do
     $~ = nil
 
@@ -543,22 +428,11 @@ describe :string_slice_string, shared: true do
     -> { "hello".send(@method, o) }.should raise_error(TypeError)
   end
 
-  ruby_version_is ''...'3.0' do
-    it "returns a subclass instance when given a subclass instance" do
-      s = StringSpecs::MyString.new("el")
-      r = "hello".send(@method, s)
-      r.should == "el"
-      r.should be_an_instance_of(StringSpecs::MyString)
-    end
-  end
-
-  ruby_version_is '3.0' do
-    it "returns a String instance when given a subclass instance" do
-      s = StringSpecs::MyString.new("el")
-      r = "hello".send(@method, s)
-      r.should == "el"
-      r.should be_an_instance_of(String)
-    end
+  it "returns a String instance when given a subclass instance" do
+    s = StringSpecs::MyString.new("el")
+    r = "hello".send(@method, s)
+    r.should == "el"
+    r.should be_an_instance_of(String)
   end
 end
 
@@ -584,30 +458,6 @@ describe :string_slice_regexp_group, shared: true do
       "hello there".send(@method, /(?<g>h(?<g>.))/, 'g').should == "e"
     end
 
-    ruby_version_is ''...'2.7' do
-      it "always taints resulting strings when self or regexp is tainted" do
-        strs = ["hello world"]
-        strs += strs.map { |s| s.dup.taint }
-
-        strs.each do |str|
-          str.send(@method, /(?<hi>hello)/, 'hi').tainted?.should == str.tainted?
-
-          str.send(@method, /(?<g>(.)(.)(.))/, 'g').tainted?.should == str.tainted?
-          str.send(@method, /(?<h>.)(.)(.)/, 'h').tainted?.should == str.tainted?
-          str.send(@method, /(.)(?<a>.)(.)/, 'a').tainted?.should == str.tainted?
-          str.send(@method, /(.)(.)(?<r>.)/, 'r').tainted?.should == str.tainted?
-          str.send(@method, /(?<h>.)(?<a>.)(?<r>.)/, 'r').tainted?.should == str.tainted?
-
-          tainted_re = /(?<a>.)(?<b>.)(?<c>.)/
-          tainted_re.taint
-
-          str.send(@method, tainted_re, 'a').tainted?.should be_true
-          str.send(@method, tainted_re, 'b').tainted?.should be_true
-          str.send(@method, tainted_re, 'c').tainted?.should be_true
-        end
-      end
-    end
-
     it "returns nil if there is no match" do
       "hello there".send(@method, /(?<whut>what?)/, 'whut').should be_nil
     end
@@ -628,18 +478,9 @@ describe :string_slice_regexp_group, shared: true do
       -> { "hello".send(@method, /(?<q>)/, '') }.should raise_error(IndexError)
     end
 
-    ruby_version_is ''...'3.0' do
-      it "returns subclass instances" do
-        s = StringSpecs::MyString.new("hello")
-        s.send(@method, /(?<q>.)/, 'q').should be_an_instance_of(StringSpecs::MyString)
-      end
-    end
-
-    ruby_version_is '3.0' do
-      it "returns String instances" do
-        s = StringSpecs::MyString.new("hello")
-        s.send(@method, /(?<q>.)/, 'q').should be_an_instance_of(String)
-      end
+    it "returns String instances" do
+      s = StringSpecs::MyString.new("hello")
+      s.send(@method, /(?<q>.)/, 'q').should be_an_instance_of(String)
     end
 
     it "sets $~ to MatchData when there is a match and nil when there's none" do
diff --git a/spec/ruby/core/string/shared/strip.rb b/spec/ruby/core/string/shared/strip.rb
new file mode 100644
index 0000000000..3af77b50fe
--- /dev/null
+++ b/spec/ruby/core/string/shared/strip.rb
@@ -0,0 +1,14 @@
+require_relative '../../../spec_helper'
+require_relative '../fixtures/classes'
+
+describe :string_strip, shared: true do
+  it "returns a String in the same encoding as self" do
+    " hello ".encode("US-ASCII").send(@method).encoding.should == Encoding::US_ASCII
+  end
+
+  it "returns String instances when called on a subclass" do
+    StringSpecs::MyString.new(" hello ").send(@method).should be_an_instance_of(String)
+    StringSpecs::MyString.new(" ").send(@method).should be_an_instance_of(String)
+    StringSpecs::MyString.new("").send(@method).should be_an_instance_of(String)
+  end
+end
diff --git a/spec/ruby/core/string/shared/succ.rb b/spec/ruby/core/string/shared/succ.rb
index 25602103b6..b69a394875 100644
--- a/spec/ruby/core/string/shared/succ.rb
+++ b/spec/ruby/core/string/shared/succ.rb
@@ -59,34 +59,21 @@ describe :string_succ, shared: true do
     "\xFF\xFF".send(@method).should == "\x01\x00\x00"
   end
 
-  ruby_version_is ''...'3.0' do
-    it "returns subclass instances when called on a subclass" do
-      StringSpecs::MyString.new("").send(@method).should be_an_instance_of(StringSpecs::MyString)
-      StringSpecs::MyString.new("a").send(@method).should be_an_instance_of(StringSpecs::MyString)
-      StringSpecs::MyString.new("z").send(@method).should be_an_instance_of(StringSpecs::MyString)
-    end
+  it "returns String instances when called on a subclass" do
+    StringSpecs::MyString.new("").send(@method).should be_an_instance_of(String)
+    StringSpecs::MyString.new("a").send(@method).should be_an_instance_of(String)
+    StringSpecs::MyString.new("z").send(@method).should be_an_instance_of(String)
   end
 
-  ruby_version_is '3.0' do
-    it "returns String instances when called on a subclass" do
-      StringSpecs::MyString.new("").send(@method).should be_an_instance_of(String)
-      StringSpecs::MyString.new("a").send(@method).should be_an_instance_of(String)
-      StringSpecs::MyString.new("z").send(@method).should be_an_instance_of(String)
-    end
-  end
-
-  ruby_version_is ''...'2.7' do
-    it "taints the result if self is tainted" do
-      ["", "a", "z", "Z", "9", "\xFF", "\xFF\xFF"].each do |s|
-        s.taint.send(@method).should.tainted?
-      end
-    end
+  it "returns a String in the same encoding as self" do
+    "z".encode("US-ASCII").send(@method).encoding.should == Encoding::US_ASCII
   end
 end
 
 describe :string_succ_bang, shared: true do
   it "is equivalent to succ, but modifies self in place (still returns self)" do
     ["", "abcd", "THX1138"].each do |s|
+      s = +s
       r = s.dup.send(@method)
       s.send(@method).should equal(s)
       s.should == r
diff --git a/spec/ruby/core/string/shared/to_a.rb b/spec/ruby/core/string/shared/to_a.rb
deleted file mode 100644
index bad3ea6584..0000000000
--- a/spec/ruby/core/string/shared/to_a.rb
+++ /dev/null
@@ -1,9 +0,0 @@
-describe :string_to_a, shared: true do
-  it "returns an empty array for empty strings" do
-    "".send(@method).should == []
-  end
-
-  it "returns an array containing the string for non-empty strings" do
-    "hello".send(@method).should == ["hello"]
-  end
-end
diff --git a/spec/ruby/core/string/shared/to_s.rb b/spec/ruby/core/string/shared/to_s.rb
index b8c9b8ab44..4b87a6cbe1 100644
--- a/spec/ruby/core/string/shared/to_s.rb
+++ b/spec/ruby/core/string/shared/to_s.rb
@@ -10,11 +10,4 @@ describe :string_to_s, shared: true do
     s.should == "a string"
     s.should be_an_instance_of(String)
   end
-
-  ruby_version_is ''...'2.7' do
-    it "taints the result when self is tainted" do
-      "x".taint.send(@method).should.tainted?
-      StringSpecs::MyString.new("x").taint.send(@method).should.tainted?
-    end
-  end
 end
diff --git a/spec/ruby/core/string/shared/to_sym.rb b/spec/ruby/core/string/shared/to_sym.rb
index 416f302aef..833eae100e 100644
--- a/spec/ruby/core/string/shared/to_sym.rb
+++ b/spec/ruby/core/string/shared/to_sym.rb
@@ -53,11 +53,20 @@ describe :string_to_sym, shared: true do
     sym.to_s.should == binary_string
   end
 
+  it "ignores existing symbols with different encoding" do
+    source = "fée"
+
+    iso_symbol = source.dup.force_encoding(Encoding::ISO_8859_1).send(@method)
+    iso_symbol.encoding.should == Encoding::ISO_8859_1
+    binary_symbol = source.dup.force_encoding(Encoding::BINARY).send(@method)
+    binary_symbol.encoding.should == Encoding::BINARY
+  end
+
   it "raises an EncodingError for UTF-8 String containing invalid bytes" do
     invalid_utf8 = "\xC3"
     invalid_utf8.should_not.valid_encoding?
     -> {
       invalid_utf8.send(@method)
-    }.should raise_error(EncodingError, /invalid/)
+    }.should raise_error(EncodingError, 'invalid symbol in encoding UTF-8 :"\xC3"')
   end
 end