14 files changed, 669 insertions, 384 deletions

diff --git a/spec/ruby/library/stringio/each_line_spec.rb b/spec/ruby/library/stringio/each_line_spec.rb
index c68f7dae82..4ac0db7c45 100644
--- a/spec/ruby/library/stringio/each_line_spec.rb
+++ b/spec/ruby/library/stringio/each_line_spec.rb
@@ -21,3 +21,7 @@ end
 describe "StringIO#each_line when passed limit" do
   it_behaves_like :stringio_each_limit, :each_line
 end
+
+describe "StringIO#each when passed separator and limit" do
+  it_behaves_like :stringio_each_separator_and_limit, :each_line
+end
diff --git a/spec/ruby/library/stringio/each_spec.rb b/spec/ruby/library/stringio/each_spec.rb
index 2c30ed5cda..7eb322f3ff 100644
--- a/spec/ruby/library/stringio/each_spec.rb
+++ b/spec/ruby/library/stringio/each_spec.rb
@@ -25,3 +25,7 @@ end
 describe "StringIO#each when passed limit" do
   it_behaves_like :stringio_each_limit, :each
 end
+
+describe "StringIO#each when passed separator and limit" do
+  it_behaves_like :stringio_each_separator_and_limit, :each
+end
diff --git a/spec/ruby/library/stringio/fileno_spec.rb b/spec/ruby/library/stringio/fileno_spec.rb
index eea03a5af3..5a9f440a0f 100644
--- a/spec/ruby/library/stringio/fileno_spec.rb
+++ b/spec/ruby/library/stringio/fileno_spec.rb
@@ -1,6 +1,5 @@
 require_relative '../../spec_helper'
-require_relative 'fixtures/classes'
-require_relative 'shared/each'
+require 'stringio'
 
 describe "StringIO#fileno" do
   it "returns nil" do
diff --git a/spec/ruby/library/stringio/fixtures/classes.rb b/spec/ruby/library/stringio/fixtures/classes.rb
index bb8dc354cc..832c5457d7 100644
--- a/spec/ruby/library/stringio/fixtures/classes.rb
+++ b/spec/ruby/library/stringio/fixtures/classes.rb
@@ -4,12 +4,12 @@ class StringSubclass < String; end
 
 module StringIOSpecs
   def self.build
-  str = <<-EOS
+    str = <<-EOS
     each
     peach
     pear
     plum
-  EOS
+    EOS
     StringIO.new(str)
   end
 end
diff --git a/spec/ruby/library/stringio/gets_spec.rb b/spec/ruby/library/stringio/gets_spec.rb
index 4af7704a41..ac876f0b4f 100644
--- a/spec/ruby/library/stringio/gets_spec.rb
+++ b/spec/ruby/library/stringio/gets_spec.rb
@@ -1,250 +1,61 @@
 require_relative '../../spec_helper'
 require "stringio"
+require_relative "shared/gets"
 
-describe "StringIO#gets when passed [separator]" do
-  before :each do
-    @io = StringIO.new("this>is>an>example")
-  end
-
-  it "returns the data read till the next occurrence of the passed separator" do
-    @io.gets(">").should == "this>"
-    @io.gets(">").should == "is>"
-    @io.gets(">").should == "an>"
-    @io.gets(">").should == "example"
-  end
-
-  it "sets $_ to the read content" do
-    @io.gets(">")
-    $_.should == "this>"
-    @io.gets(">")
-    $_.should == "is>"
-    @io.gets(">")
-    $_.should == "an>"
-    @io.gets(">")
-    $_.should == "example"
-    @io.gets(">")
-    $_.should be_nil
-  end
-
-  it "accepts string as separator" do
-    @io.gets("is>")
-    $_.should == "this>"
-    @io.gets("an>")
-    $_.should == "is>an>"
-    @io.gets("example")
-    $_.should == "example"
-    @io.gets("ple")
-    $_.should be_nil
-  end
-
-  it "updates self's lineno by one" do
-    @io.gets(">")
-    @io.lineno.should eql(1)
-
-    @io.gets(">")
-    @io.lineno.should eql(2)
-
-    @io.gets(">")
-    @io.lineno.should eql(3)
-  end
-
-  it "returns the next paragraph when the passed separator is an empty String" do
-    io = StringIO.new("this is\n\nan example")
-    io.gets("").should == "this is\n\n"
-    io.gets("").should == "an example"
-  end
-
-  it "returns the remaining content starting at the current position when passed nil" do
-    io = StringIO.new("this is\n\nan example")
-    io.pos = 5
-    io.gets(nil).should == "is\n\nan example"
-  end
+describe "StringIO#gets" do
+  describe "when passed [separator]" do
+    it_behaves_like :stringio_gets_separator, :gets
 
-  it "tries to convert the passed separator to a String using #to_str" do
-    obj = mock('to_str')
-    obj.should_receive(:to_str).and_return(">")
-    @io.gets(obj).should == "this>"
-  end
-end
-
-describe "StringIO#gets when passed no argument" do
-  before :each do
-    @io = StringIO.new("this is\nan example\nfor StringIO#gets")
-  end
+    it "returns nil if self is at the end" do
+      @io = StringIO.new("this>is>an>example")
 
-  it "returns the data read till the next occurrence of $/ or till eof" do
-    @io.gets.should == "this is\n"
-
-    begin
-      old_sep = $/
-      suppress_warning {$/ = " "}
-      @io.gets.should == "an "
-      @io.gets.should == "example\nfor "
-      @io.gets.should == "StringIO#gets"
-    ensure
-      suppress_warning {$/ = old_sep}
+      @io.pos = 36
+      @io.gets(">").should be_nil
+      @io.gets(">").should be_nil
     end
   end
 
-  it "sets $_ to the read content" do
-    @io.gets
-    $_.should == "this is\n"
-    @io.gets
-    $_.should == "an example\n"
-    @io.gets
-    $_.should == "for StringIO#gets"
-    @io.gets
-    $_.should be_nil
-  end
-
-  it "updates self's position" do
-    @io.gets
-    @io.pos.should eql(8)
-
-    @io.gets
-    @io.pos.should eql(19)
-
-    @io.gets
-    @io.pos.should eql(36)
-  end
-
-  it "updates self's lineno" do
-    @io.gets
-    @io.lineno.should eql(1)
-
-    @io.gets
-    @io.lineno.should eql(2)
-
-    @io.gets
-    @io.lineno.should eql(3)
-  end
-
-  it "returns nil if self is at the end" do
-    @io.pos = 36
-    @io.gets.should be_nil
-    @io.gets.should be_nil
-  end
-end
-
-describe "StringIO#gets when passed [limit]" do
-  before :each do
-    @io = StringIO.new("this>is>an>example")
-  end
-
-  it "returns the data read until the limit is met" do
-    @io.gets(4).should == "this"
-    @io.gets(3).should == ">is"
-    @io.gets(5).should == ">an>e"
-    @io.gets(6).should == "xample"
-  end
-
-  it "sets $_ to the read content" do
-    @io.gets(4)
-    $_.should == "this"
-    @io.gets(3)
-    $_.should == ">is"
-    @io.gets(5)
-    $_.should == ">an>e"
-    @io.gets(6)
-    $_.should == "xample"
-    @io.gets(3)
-    $_.should be_nil
-  end
-
-  it "updates self's lineno by one" do
-    @io.gets(3)
-    @io.lineno.should eql(1)
-
-    @io.gets(3)
-    @io.lineno.should eql(2)
-
-    @io.gets(3)
-    @io.lineno.should eql(3)
-  end
-
-  it "tries to convert the passed limit to an Integer using #to_int" do
-    obj = mock('to_int')
-    obj.should_receive(:to_int).and_return(4)
-    @io.gets(obj).should == "this"
-  end
-
-  it "returns a blank string when passed a limit of 0" do
-    @io.gets(0).should == ""
-  end
-
-  it "ignores it when passed a negative limit" do
-    @io.gets(-4).should == "this>is>an>example"
-  end
-end
+  describe "when passed [limit]" do
+    it_behaves_like :stringio_gets_limit, :gets
 
-describe "StringIO#gets when passed [separator] and [limit]" do
-  before :each do
-    @io = StringIO.new("this>is>an>example")
-  end
-
-  it "returns the data read until the limit is consumed or the separator is met" do
-    @io.gets('>', 8).should == "this>"
-    @io.gets('>', 2).should == "is"
-    @io.gets('>', 10).should == ">"
-    @io.gets('>', 6).should == "an>"
-    @io.gets('>', 5).should == "examp"
-  end
+    it "returns nil if self is at the end" do
+      @io = StringIO.new("this>is>an>example")
 
-  it "sets $_ to the read content" do
-    @io.gets('>', 8)
-    $_.should == "this>"
-    @io.gets('>', 2)
-    $_.should == "is"
-    @io.gets('>', 10)
-    $_.should == ">"
-    @io.gets('>', 6)
-    $_.should == "an>"
-    @io.gets('>', 5)
-    $_.should == "examp"
+      @io.pos = 36
+      @io.gets(3).should be_nil
+      @io.gets(3).should be_nil
+    end
   end
 
-  it "updates self's lineno by one" do
-    @io.gets('>', 3)
-    @io.lineno.should eql(1)
+  describe "when passed [separator] and [limit]" do
+    it_behaves_like :stringio_gets_separator_and_limit, :gets
 
-    @io.gets('>', 3)
-    @io.lineno.should eql(2)
+    it "returns nil if self is at the end" do
+      @io = StringIO.new("this>is>an>example")
 
-    @io.gets('>', 3)
-    @io.lineno.should eql(3)
+      @io.pos = 36
+      @io.gets(">", 3).should be_nil
+      @io.gets(">", 3).should be_nil
+    end
   end
 
-  it "tries to convert the passed separator to a String using #to_str" do
-    obj = mock('to_str')
-    obj.should_receive(:to_str).and_return('>')
-    @io.gets(obj, 5).should == "this>"
-  end
+  describe "when passed no argument" do
+    it_behaves_like :stringio_gets_no_argument, :gets
 
-  it "does not raise TypeError if passed separator is nil" do
-    @io.gets(nil, 5).should == "this>"
-  end
+    it "returns nil if self is at the end" do
+      @io = StringIO.new("this>is>an>example")
 
-  it "tries to convert the passed limit to an Integer using #to_int" do
-    obj = mock('to_int')
-    obj.should_receive(:to_int).and_return(5)
-    @io.gets('>', obj).should == "this>"
+      @io.pos = 36
+      @io.gets.should be_nil
+      @io.gets.should be_nil
+    end
   end
-end
-
-describe "StringIO#gets when in write-only mode" do
-  it "raises an IOError" do
-    io = StringIO.new(+"xyz", "w")
-    -> { io.gets }.should raise_error(IOError)
 
-    io = StringIO.new("xyz")
-    io.close_read
-    -> { io.gets }.should raise_error(IOError)
+  describe "when passed [chomp]" do
+    it_behaves_like :stringio_gets_chomp, :gets
   end
-end
 
-describe "StringIO#gets when passed [chomp]" do
-  it "returns the data read without a trailing newline character" do
-    io = StringIO.new("this>is>an>example\n")
-    io.gets(chomp: true).should == "this>is>an>example"
+  describe "when in write-only mode" do
+    it_behaves_like :stringio_gets_write_only, :gets
   end
 end
diff --git a/spec/ruby/library/stringio/readline_spec.rb b/spec/ruby/library/stringio/readline_spec.rb
index b16a16e23f..085360707f 100644
--- a/spec/ruby/library/stringio/readline_spec.rb
+++ b/spec/ruby/library/stringio/readline_spec.rb
@@ -1,150 +1,58 @@
 require_relative '../../spec_helper'
+require "stringio"
 require_relative 'fixtures/classes'
+require_relative "shared/gets"
 
+describe "StringIO#readline" do
+  describe "when passed [separator]" do
+    it_behaves_like :stringio_gets_separator, :readline
 
-describe "StringIO#readline when passed [separator]" do
-  before :each do
-    @io = StringIO.new("this>is>an>example")
-  end
-
-  it "returns the data read till the next occurrence of the passed separator" do
-    @io.readline(">").should == "this>"
-    @io.readline(">").should == "is>"
-    @io.readline(">").should == "an>"
-    @io.readline(">").should == "example"
-  end
-
-  it "sets $_ to the read content" do
-    @io.readline(">")
-    $_.should == "this>"
-    @io.readline(">")
-    $_.should == "is>"
-    @io.readline(">")
-    $_.should == "an>"
-    @io.readline(">")
-    $_.should == "example"
-  end
-
-  it "updates self's lineno by one" do
-    @io.readline(">")
-    @io.lineno.should eql(1)
-
-    @io.readline(">")
-    @io.lineno.should eql(2)
-
-    @io.readline(">")
-    @io.lineno.should eql(3)
-  end
-
-  it "returns the next paragraph when the passed separator is an empty String" do
-    io = StringIO.new("this is\n\nan example")
-    io.readline("").should == "this is\n\n"
-    io.readline("").should == "an example"
-  end
-
-  it "returns the remaining content starting at the current position when passed nil" do
-    io = StringIO.new("this is\n\nan example")
-    io.pos = 5
-    io.readline(nil).should == "is\n\nan example"
-  end
-
-  it "tries to convert the passed separator to a String using #to_str" do
-    obj = mock('to_str')
-    obj.should_receive(:to_str).and_return(">")
-    @io.readline(obj).should == "this>"
-  end
-end
-
-describe "StringIO#readline when passed no argument" do
-  before :each do
-    @io = StringIO.new("this is\nan example\nfor StringIO#readline")
-  end
-
-  it "returns the data read till the next occurrence of $/ or till eof" do
-    @io.readline.should == "this is\n"
+    it "raises an IOError if self is at the end" do
+      @io = StringIO.new("this>is>an>example")
 
-    begin
-      old_sep = $/
-      suppress_warning {$/ = " "}
-      @io.readline.should == "an "
-      @io.readline.should == "example\nfor "
-      @io.readline.should == "StringIO#readline"
-    ensure
-      suppress_warning {$/ = old_sep}
+      @io.pos = 36
+      -> { @io.readline(">") }.should raise_error(IOError)
     end
   end
 
-  it "sets $_ to the read content" do
-    @io.readline
-    $_.should == "this is\n"
-    @io.readline
-    $_.should == "an example\n"
-    @io.readline
-    $_.should == "for StringIO#readline"
-  end
+  describe "when passed [limit]" do
+    it_behaves_like :stringio_gets_limit, :readline
 
-  it "updates self's position" do
-    @io.readline
-    @io.pos.should eql(8)
+    it "raises an IOError if self is at the end" do
+      @io = StringIO.new("this>is>an>example")
 
-    @io.readline
-    @io.pos.should eql(19)
-
-    @io.readline
-    @io.pos.should eql(40)
+      @io.pos = 36
+      -> { @io.readline(3) }.should raise_error(IOError)
+    end
   end
 
-  it "updates self's lineno" do
-    @io.readline
-    @io.lineno.should eql(1)
+  describe "when passed [separator] and [limit]" do
+    it_behaves_like :stringio_gets_separator_and_limit, :readline
 
-    @io.readline
-    @io.lineno.should eql(2)
+    it "raises an IOError if self is at the end" do
+      @io = StringIO.new("this>is>an>example")
 
-    @io.readline
-    @io.lineno.should eql(3)
-  end
-
-  it "raises an IOError if self is at the end" do
-    @io.pos = 40
-    -> { @io.readline }.should raise_error(IOError)
-  end
-end
-
-describe "StringIO#readline when in write-only mode" do
-  it "raises an IOError" do
-    io = StringIO.new(+"xyz", "w")
-    -> { io.readline }.should raise_error(IOError)
-
-    io = StringIO.new("xyz")
-    io.close_read
-    -> { io.readline }.should raise_error(IOError)
+      @io.pos = 36
+      -> { @io.readline(">", 3) }.should raise_error(IOError)
+    end
   end
-end
 
-describe "StringIO#readline when passed [chomp]" do
-  it "returns the data read without a trailing newline character" do
-    io = StringIO.new("this>is>an>example\n")
-    io.readline(chomp: true).should == "this>is>an>example"
-  end
-end
+  describe "when passed no argument" do
+    it_behaves_like :stringio_gets_no_argument, :readline
 
-describe "StringIO#readline when passed [limit]" do
-  before :each do
-    @io = StringIO.new("this>is>an>example")
-  end
+    it "raises an IOError if self is at the end" do
+      @io = StringIO.new("this>is>an>example")
 
-  it "returns the data read until the limit is met" do
-    io = StringIO.new("this>is>an>example\n")
-    io.readline(3).should == "thi"
+      @io.pos = 36
+      -> { @io.readline }.should raise_error(IOError)
+    end
   end
 
-  it "returns a blank string when passed a limit of 0" do
-    @io.readline(0).should == ""
+  describe "when passed [chomp]" do
+    it_behaves_like :stringio_gets_chomp, :readline
   end
 
-  it "ignores it when the limit is negative" do
-    seen = []
-    @io.readline(-4).should == "this>is>an>example"
+  describe "when in write-only mode" do
+    it_behaves_like :stringio_gets_write_only, :readline
   end
 end
diff --git a/spec/ruby/library/stringio/readpartial_spec.rb b/spec/ruby/library/stringio/readpartial_spec.rb
index f25cef4014..dadefb7837 100644
--- a/spec/ruby/library/stringio/readpartial_spec.rb
+++ b/spec/ruby/library/stringio/readpartial_spec.rb
@@ -10,13 +10,7 @@ describe "StringIO#readpartial" do
     @string.close unless @string.closed?
   end
 
-  it "raises IOError on closed stream" do
-    @string.close
-    -> { @string.readpartial(10) }.should raise_error(IOError)
-  end
-
   it "reads at most the specified number of bytes" do
-
     # buffered read
     @string.read(1).should == 'S'
     # return only specified number, not the whole buffer
@@ -30,6 +24,14 @@ describe "StringIO#readpartial" do
     @string.readpartial(3).should == ", l"
   end
 
+  it "reads after ungetc with multibyte characters in the buffer" do
+    @string = StringIO.new(+"∂φ/∂x = gaîté")
+    c = @string.getc
+    @string.ungetc(c)
+    @string.readpartial(3).should == "\xE2\x88\x82".b
+    @string.readpartial(3).should == "\xCF\x86/".b
+  end
+
   it "reads after ungetc without data in the buffer" do
     @string = StringIO.new
     @string.write("f").should == 1
@@ -67,14 +69,34 @@ describe "StringIO#readpartial" do
 
   it "raises IOError if the stream is closed" do
     @string.close
-    -> { @string.readpartial(1) }.should raise_error(IOError)
+    -> { @string.readpartial(1) }.should raise_error(IOError, "not opened for reading")
   end
 
   it "raises ArgumentError if the negative argument is provided" do
-    -> { @string.readpartial(-1) }.should raise_error(ArgumentError)
+    -> { @string.readpartial(-1) }.should raise_error(ArgumentError, "negative length -1 given")
   end
 
   it "immediately returns an empty string if the length argument is 0" do
     @string.readpartial(0).should == ""
   end
+
+  it "raises IOError if the stream is closed and the length argument is 0" do
+    @string.close
+    -> { @string.readpartial(0) }.should raise_error(IOError, "not opened for reading")
+  end
+
+  it "clears and returns the given buffer if the length argument is 0" do
+    buffer = +"existing content"
+    @string.readpartial(0, buffer).should == buffer
+    buffer.should == ""
+  end
+
+  version_is StringIO::VERSION, "3.1.2" do # ruby_version_is "3.4"
+    it "preserves the encoding of the given buffer" do
+      buffer = ''.encode(Encoding::ISO_8859_1)
+      @string.readpartial(10, buffer)
+
+      buffer.encoding.should == Encoding::ISO_8859_1
+    end
+  end
 end
diff --git a/spec/ruby/library/stringio/set_encoding_by_bom_spec.rb b/spec/ruby/library/stringio/set_encoding_by_bom_spec.rb
new file mode 100644
index 0000000000..1030aad042
--- /dev/null
+++ b/spec/ruby/library/stringio/set_encoding_by_bom_spec.rb
@@ -0,0 +1,237 @@
+require 'stringio'
+require_relative '../../spec_helper'
+
+# Should be synced with specs for IO#set_encoding_by_bom
+describe "StringIO#set_encoding_by_bom" do
+  it "returns nil if not readable" do
+    io = StringIO.new("".b, "wb")
+
+    io.set_encoding_by_bom.should be_nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+  end
+
+  it "returns the result encoding if found BOM UTF-8 sequence" do
+    io = StringIO.new("\u{FEFF}".b, "rb")
+
+    io.set_encoding_by_bom.should == Encoding::UTF_8
+    io.external_encoding.should == Encoding::UTF_8
+    io.read.b.should == "".b
+
+    io = StringIO.new("\u{FEFF}abc".b, "rb")
+
+    io.set_encoding_by_bom.should == Encoding::UTF_8
+    io.external_encoding.should == Encoding::UTF_8
+    io.read.b.should == "abc".b
+  end
+
+  it "returns the result encoding if found BOM UTF_16LE sequence" do
+    io = StringIO.new("\xFF\xFE".b, "rb")
+
+    io.set_encoding_by_bom.should == Encoding::UTF_16LE
+    io.external_encoding.should == Encoding::UTF_16LE
+    io.read.b.should == "".b
+
+    io = StringIO.new("\xFF\xFEabc".b, "rb")
+
+    io.set_encoding_by_bom.should == Encoding::UTF_16LE
+    io.external_encoding.should == Encoding::UTF_16LE
+    io.read.b.should == "abc".b
+  end
+
+  it "returns the result encoding if found BOM UTF_16BE sequence" do
+    io = StringIO.new("\xFE\xFF".b, "rb")
+
+    io.set_encoding_by_bom.should == Encoding::UTF_16BE
+    io.external_encoding.should == Encoding::UTF_16BE
+    io.read.b.should == "".b
+
+    io = StringIO.new("\xFE\xFFabc".b, "rb")
+
+    io.set_encoding_by_bom.should == Encoding::UTF_16BE
+    io.external_encoding.should == Encoding::UTF_16BE
+    io.read.b.should == "abc".b
+  end
+
+  it "returns the result encoding if found BOM UTF_32LE sequence" do
+    io = StringIO.new("\xFF\xFE\x00\x00".b, "rb")
+
+    io.set_encoding_by_bom.should == Encoding::UTF_32LE
+    io.external_encoding.should == Encoding::UTF_32LE
+    io.read.b.should == "".b
+
+    io = StringIO.new("\xFF\xFE\x00\x00abc".b, "rb")
+
+    io.set_encoding_by_bom.should == Encoding::UTF_32LE
+    io.external_encoding.should == Encoding::UTF_32LE
+    io.read.b.should == "abc".b
+  end
+
+  it "returns the result encoding if found BOM UTF_32BE sequence" do
+    io = StringIO.new("\x00\x00\xFE\xFF".b, "rb")
+
+    io.set_encoding_by_bom.should == Encoding::UTF_32BE
+    io.external_encoding.should == Encoding::UTF_32BE
+    io.read.b.should == "".b
+
+    io = StringIO.new("\x00\x00\xFE\xFFabc".b, "rb")
+
+    io.set_encoding_by_bom.should == Encoding::UTF_32BE
+    io.external_encoding.should == Encoding::UTF_32BE
+    io.read.b.should == "abc".b
+  end
+
+  it "returns nil if io is empty" do
+    io = StringIO.new("".b, "rb")
+    io.set_encoding_by_bom.should be_nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+  end
+
+  it "returns nil if UTF-8 BOM sequence is incomplete" do
+    io = StringIO.new("\xEF".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read.b.should == "\xEF".b
+
+    io = StringIO.new("\xEFa".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read.b.should == "\xEFa".b
+
+    io = StringIO.new("\xEF\xBB".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read.b.should == "\xEF\xBB".b
+
+    io = StringIO.new("\xEF\xBBa".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read.b.should == "\xEF\xBBa".b
+  end
+
+  it "returns nil if UTF-16BE BOM sequence is incomplete" do
+    io = StringIO.new("\xFE".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read.b.should == "\xFE".b
+
+    io = StringIO.new("\xFEa".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read.b.should == "\xFEa".b
+  end
+
+  it "returns nil if UTF-16LE/UTF-32LE BOM sequence is incomplete" do
+    io = StringIO.new("\xFF".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read.b.should == "\xFF".b
+
+    io = StringIO.new("\xFFa".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read.b.should == "\xFFa".b
+  end
+
+  it "returns UTF-16LE if UTF-32LE BOM sequence is incomplete" do
+    io = StringIO.new("\xFF\xFE".b, "rb")
+
+    io.set_encoding_by_bom.should == Encoding::UTF_16LE
+    io.external_encoding.should == Encoding::UTF_16LE
+    io.read.b.should == "".b
+
+    io = StringIO.new("\xFF\xFE\x00".b, "rb")
+
+    io.set_encoding_by_bom.should == Encoding::UTF_16LE
+    io.external_encoding.should == Encoding::UTF_16LE
+    io.read.b.should == "\x00".b
+
+    io = StringIO.new("\xFF\xFE\x00a".b, "rb")
+
+    io.set_encoding_by_bom.should == Encoding::UTF_16LE
+    io.external_encoding.should == Encoding::UTF_16LE
+    io.read.b.should == "\x00a".b
+  end
+
+  it "returns nil if UTF-32BE BOM sequence is incomplete" do
+    io = StringIO.new("\x00".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read.b.should == "\x00".b
+
+    io = StringIO.new("\x00a".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read.b.should == "\x00a".b
+
+    io = StringIO.new("\x00\x00".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read.b.should == "\x00\x00".b
+
+    io = StringIO.new("\x00\x00a".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read.b.should == "\x00\x00a".b
+
+    io = StringIO.new("\x00\x00\xFE".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read.b.should == "\x00\x00\xFE".b
+
+    io = StringIO.new("\x00\x00\xFEa".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read.b.should == "\x00\x00\xFEa".b
+  end
+
+  it "returns nil if found BOM sequence not provided" do
+    io = StringIO.new("abc".b, "rb")
+
+    io.set_encoding_by_bom.should == nil
+    io.external_encoding.should == Encoding::ASCII_8BIT
+    io.read(3).should == "abc".b
+  end
+
+  it "does not raise exception if io not in binary mode" do
+    io = StringIO.new("", 'r')
+    io.set_encoding_by_bom.should == nil
+  end
+
+  it "does not raise exception if encoding already set" do
+    io = StringIO.new("".b, "rb")
+    io.set_encoding("utf-8")
+    io.set_encoding_by_bom.should == nil
+  end
+
+  it "does not raise exception if encoding conversion is already set" do
+    io = StringIO.new("".b, "rb")
+    io.set_encoding(Encoding::UTF_8, Encoding::UTF_16BE)
+
+    io.set_encoding_by_bom.should == nil
+  end
+
+  it "raises FrozenError when io is frozen" do
+    io = StringIO.new()
+    io.freeze
+    -> { io.set_encoding_by_bom }.should raise_error(FrozenError)
+  end
+
+  it "does not raise FrozenError when initial string is frozen" do
+    io = StringIO.new("".freeze)
+    io.set_encoding_by_bom.should == nil
+  end
+end
diff --git a/spec/ruby/library/stringio/shared/each.rb b/spec/ruby/library/stringio/shared/each.rb
index e0dd3f9b8f..626b41a4d3 100644
--- a/spec/ruby/library/stringio/shared/each.rb
+++ b/spec/ruby/library/stringio/shared/each.rb
@@ -36,22 +36,11 @@ describe :stringio_each_separator, shared: true do
     seen.should == ["2 1 2 1 2"]
   end
 
-  version_is StringIO::VERSION, ""..."3.0.4" do #ruby_version_is ""..."3.2" do
-    it "yields each paragraph with two separation characters when passed an empty String as separator" do
-      seen = []
-      io = StringIO.new("para1\n\npara2\n\n\npara3")
-      io.send(@method, "") {|s| seen << s}
-      seen.should == ["para1\n\n", "para2\n\n", "para3"]
-    end
-  end
-
-  version_is StringIO::VERSION, "3.0.4" do #ruby_version_is "3.2" do
-    it "yields each paragraph with all separation characters when passed an empty String as separator" do
-      seen = []
-      io = StringIO.new("para1\n\npara2\n\n\npara3")
-      io.send(@method, "") {|s| seen << s}
-      seen.should == ["para1\n\n", "para2\n\n\n", "para3"]
-    end
+  it "yields each paragraph with all separation characters when passed an empty String as separator" do
+    seen = []
+    io = StringIO.new("para1\n\npara2\n\n\npara3")
+    io.send(@method, "") {|s| seen << s}
+    seen.should == ["para1\n\n", "para2\n\n\n", "para3"]
   end
 end
 
@@ -161,3 +150,60 @@ describe :stringio_each_limit, shared: true do
     seen.should == ["a b ", "c d ", "e\n", "1 2 ", "3 4 ", "5"]
   end
 end
+
+describe :stringio_each_separator_and_limit, shared: true do
+  before :each do
+    @io = StringIO.new("this>is>an>example")
+  end
+
+  it "returns the data read until the limit is consumed or the separator is met" do
+    @io.send(@method, '>', 8) { |s| break s }.should == "this>"
+    @io.send(@method, '>', 2) { |s| break s }.should == "is"
+    @io.send(@method, '>', 10) { |s| break s }.should == ">"
+    @io.send(@method, '>', 6) { |s| break s }.should == "an>"
+    @io.send(@method, '>', 5) { |s| break s }.should == "examp"
+  end
+
+  it "truncates the multi-character separator at the end to meet the limit" do
+    @io.send(@method, "is>an", 7) { |s| break s }.should == "this>is"
+  end
+
+  it "does not change $_" do
+    $_ = "test"
+    @io.send(@method, '>', 8) { |s| s }
+    $_.should == "test"
+  end
+
+  it "updates self's lineno by one" do
+    @io.send(@method, '>', 3) { |s| break s }
+    @io.lineno.should eql(1)
+
+    @io.send(@method, '>', 3) { |s| break s }
+    @io.lineno.should eql(2)
+
+    @io.send(@method, '>', 3) { |s| break s }
+    @io.lineno.should eql(3)
+  end
+
+  it "tries to convert the passed separator to a String using #to_str" do # TODO
+    obj = mock('to_str')
+    obj.should_receive(:to_str).and_return('>')
+
+    seen = []
+    @io.send(@method, obj, 5) { |s| seen << s }
+    seen.should == ["this>", "is>", "an>", "examp", "le"]
+  end
+
+  it "does not raise TypeError if passed separator is nil" do
+    @io.send(@method, nil, 5) { |s| break s }.should == "this>"
+  end
+
+  it "tries to convert the passed limit to an Integer using #to_int" do # TODO
+    obj = mock('to_int')
+    obj.should_receive(:to_int).and_return(5)
+
+    seen = []
+    @io.send(@method, '>', obj) { |s| seen << s }
+    seen.should == ["this>", "is>", "an>", "examp", "le"]
+  end
+end
diff --git a/spec/ruby/library/stringio/shared/gets.rb b/spec/ruby/library/stringio/shared/gets.rb
new file mode 100644
index 0000000000..8396b161f1
--- /dev/null
+++ b/spec/ruby/library/stringio/shared/gets.rb
@@ -0,0 +1,249 @@
+describe :stringio_gets_separator, shared: true do
+  describe "when passed [separator]" do
+    before :each do
+      @io = StringIO.new("this>is>an>example")
+    end
+
+    it "returns the data read till the next occurrence of the passed separator" do
+      @io.send(@method, ">").should == "this>"
+      @io.send(@method, ">").should == "is>"
+      @io.send(@method, ">").should == "an>"
+      @io.send(@method, ">").should == "example"
+    end
+
+    it "sets $_ to the read content" do
+      @io.send(@method, ">")
+      $_.should == "this>"
+      @io.send(@method, ">")
+      $_.should == "is>"
+      @io.send(@method, ">")
+      $_.should == "an>"
+      @io.send(@method, ">")
+      $_.should == "example"
+    end
+
+    it "accepts string as separator" do
+      @io.send(@method, "is>")
+      $_.should == "this>"
+      @io.send(@method, "an>")
+      $_.should == "is>an>"
+      @io.send(@method, "example")
+      $_.should == "example"
+    end
+
+    it "updates self's lineno by one" do
+      @io.send(@method, ">")
+      @io.lineno.should eql(1)
+
+      @io.send(@method, ">")
+      @io.lineno.should eql(2)
+
+      @io.send(@method, ">")
+      @io.lineno.should eql(3)
+    end
+
+    it "returns the next paragraph when the passed separator is an empty String" do
+      io = StringIO.new("this is\n\nan example")
+      io.send(@method, "").should == "this is\n\n"
+      io.send(@method, "").should == "an example"
+    end
+
+    it "returns the remaining content starting at the current position when passed nil" do
+      io = StringIO.new("this is\n\nan example")
+      io.pos = 5
+      io.send(@method, nil).should == "is\n\nan example"
+    end
+
+    it "tries to convert the passed separator to a String using #to_str" do
+      obj = mock('to_str')
+      obj.should_receive(:to_str).and_return(">")
+      @io.send(@method, obj).should == "this>"
+    end
+  end
+end
+
+describe :stringio_gets_limit, shared: true do
+  describe "when passed [limit]" do
+    before :each do
+      @io = StringIO.new("this>is>an>example")
+    end
+
+    it "returns the data read until the limit is met" do
+      @io.send(@method, 4).should == "this"
+      @io.send(@method, 3).should == ">is"
+      @io.send(@method, 5).should == ">an>e"
+      @io.send(@method, 6).should == "xample"
+    end
+
+    it "sets $_ to the read content" do
+      @io.send(@method, 4)
+      $_.should == "this"
+      @io.send(@method, 3)
+      $_.should == ">is"
+      @io.send(@method, 5)
+      $_.should == ">an>e"
+      @io.send(@method, 6)
+      $_.should == "xample"
+    end
+
+    it "updates self's lineno by one" do
+      @io.send(@method, 3)
+      @io.lineno.should eql(1)
+
+      @io.send(@method, 3)
+      @io.lineno.should eql(2)
+
+      @io.send(@method, 3)
+      @io.lineno.should eql(3)
+    end
+
+    it "tries to convert the passed limit to an Integer using #to_int" do
+      obj = mock('to_int')
+      obj.should_receive(:to_int).and_return(4)
+      @io.send(@method, obj).should == "this"
+    end
+
+    it "returns a blank string when passed a limit of 0" do
+      @io.send(@method, 0).should == ""
+    end
+
+    it "ignores it when passed a negative limit" do
+      @io.send(@method, -4).should == "this>is>an>example"
+    end
+  end
+end
+
+describe :stringio_gets_separator_and_limit, shared: true do
+  describe "when passed [separator] and [limit]" do
+    before :each do
+      @io = StringIO.new("this>is>an>example")
+    end
+
+    it "returns the data read until the limit is consumed or the separator is met" do
+      @io.send(@method, '>', 8).should == "this>"
+      @io.send(@method, '>', 2).should == "is"
+      @io.send(@method, '>', 10).should == ">"
+      @io.send(@method, '>', 6).should == "an>"
+      @io.send(@method, '>', 5).should == "examp"
+    end
+
+    it "truncates the multi-character separator at the end to meet the limit" do
+      @io.send(@method, "is>an", 7).should == "this>is"
+    end
+
+    it "sets $_ to the read content" do
+      @io.send(@method, '>', 8)
+      $_.should == "this>"
+      @io.send(@method, '>', 2)
+      $_.should == "is"
+      @io.send(@method, '>', 10)
+      $_.should == ">"
+      @io.send(@method, '>', 6)
+      $_.should == "an>"
+      @io.send(@method, '>', 5)
+      $_.should == "examp"
+    end
+
+    it "updates self's lineno by one" do
+      @io.send(@method, '>', 3)
+      @io.lineno.should eql(1)
+
+      @io.send(@method, '>', 3)
+      @io.lineno.should eql(2)
+
+      @io.send(@method, '>', 3)
+      @io.lineno.should eql(3)
+    end
+
+    it "tries to convert the passed separator to a String using #to_str" do
+      obj = mock('to_str')
+      obj.should_receive(:to_str).and_return('>')
+      @io.send(@method, obj, 5).should == "this>"
+    end
+
+    it "does not raise TypeError if passed separator is nil" do
+      @io.send(@method, nil, 5).should == "this>"
+    end
+
+    it "tries to convert the passed limit to an Integer using #to_int" do
+      obj = mock('to_int')
+      obj.should_receive(:to_int).and_return(5)
+      @io.send(@method, '>', obj).should == "this>"
+    end
+  end
+end
+
+describe :stringio_gets_no_argument, shared: true do
+  describe "when passed no argument" do
+    before :each do
+      @io = StringIO.new("this is\nan example\nfor StringIO#gets")
+    end
+
+    it "returns the data read till the next occurrence of $/ or till eof" do
+      @io.send(@method).should == "this is\n"
+
+      begin
+        old_sep = $/
+        suppress_warning {$/ = " "}
+        @io.send(@method).should == "an "
+        @io.send(@method).should == "example\nfor "
+        @io.send(@method).should == "StringIO#gets"
+      ensure
+        suppress_warning {$/ = old_sep}
+      end
+    end
+
+    it "sets $_ to the read content" do
+      @io.send(@method)
+      $_.should == "this is\n"
+      @io.send(@method)
+      $_.should == "an example\n"
+      @io.send(@method)
+      $_.should == "for StringIO#gets"
+    end
+
+    it "updates self's position" do
+      @io.send(@method)
+      @io.pos.should eql(8)
+
+      @io.send(@method)
+      @io.pos.should eql(19)
+
+      @io.send(@method)
+      @io.pos.should eql(36)
+    end
+
+    it "updates self's lineno" do
+      @io.send(@method)
+      @io.lineno.should eql(1)
+
+      @io.send(@method)
+      @io.lineno.should eql(2)
+
+      @io.send(@method)
+      @io.lineno.should eql(3)
+    end
+  end
+end
+
+describe :stringio_gets_chomp, shared: true do
+  describe "when passed [chomp]" do
+    it "returns the data read without a trailing newline character" do
+      io = StringIO.new("this>is>an>example\n")
+      io.send(@method, chomp: true).should == "this>is>an>example"
+    end
+  end
+end
+
+describe :stringio_gets_write_only, shared: true do
+  describe "when in write-only mode" do
+    it "raises an IOError" do
+      io = StringIO.new(+"xyz", "w")
+      -> { io.send(@method) }.should raise_error(IOError)
+
+      io = StringIO.new("xyz")
+      io.close_read
+      -> { io.send(@method) }.should raise_error(IOError)
+    end
+  end
+end
diff --git a/spec/ruby/library/stringio/shared/read.rb b/spec/ruby/library/stringio/shared/read.rb
index 8ef6ec2734..22f76b0fb0 100644
--- a/spec/ruby/library/stringio/shared/read.rb
+++ b/spec/ruby/library/stringio/shared/read.rb
@@ -15,7 +15,7 @@ describe :stringio_read, shared: true do
     buffer.should == "example"
   end
 
-  ruby_version_is ""..."3.4" do
+  guard -> { StringIO::VERSION < "3.1.2" } do
     it "does not preserve the encoding of the given buffer" do
       buffer = ''.encode(Encoding::ISO_8859_1)
       @io.send(@method, 7, buffer)
@@ -24,7 +24,7 @@ describe :stringio_read, shared: true do
     end
   end
 
-  ruby_version_is "3.4" do
+  guard -> { StringIO::VERSION >= "3.1.2" } do
     it "preserves the encoding of the given buffer" do
       buffer = ''.encode(Encoding::ISO_8859_1)
       @io.send(@method, 7, buffer)
diff --git a/spec/ruby/library/stringio/shared/sysread.rb b/spec/ruby/library/stringio/shared/sysread.rb
index 937bac705c..3e23fbc233 100644
--- a/spec/ruby/library/stringio/shared/sysread.rb
+++ b/spec/ruby/library/stringio/shared/sysread.rb
@@ -10,6 +10,6 @@ describe :stringio_sysread_length, shared: true do
 
   it "raises an EOFError when passed length > 0 and no data remains" do
     @io.read.should == "example"
-    -> { @io.sysread(1) }.should raise_error(EOFError)
+    -> { @io.send(@method, 1) }.should raise_error(EOFError)
   end
 end
diff --git a/spec/ruby/library/stringio/shared/write.rb b/spec/ruby/library/stringio/shared/write.rb
index 404e08b93d..4661658baf 100644
--- a/spec/ruby/library/stringio/shared/write.rb
+++ b/spec/ruby/library/stringio/shared/write.rb
@@ -94,7 +94,7 @@ describe :stringio_write_string, shared: true do
   end
 
   it "does not transcode the given string when the external encoding is set and the string encoding is BINARY" do
-    str = "été".b
+    str = "été_".b
     io = StringIO.new.set_encoding(Encoding::UTF_16BE)
     io.external_encoding.should == Encoding::UTF_16BE
 
diff --git a/spec/ruby/library/stringio/sysread_spec.rb b/spec/ruby/library/stringio/sysread_spec.rb
index 8f78073f42..fabb06dd9a 100644
--- a/spec/ruby/library/stringio/sysread_spec.rb
+++ b/spec/ruby/library/stringio/sysread_spec.rb
@@ -1,6 +1,7 @@
 require_relative '../../spec_helper'
 require "stringio"
 require_relative 'shared/read'
+require_relative 'shared/sysread'
 
 describe "StringIO#sysread when passed length, buffer" do
   it_behaves_like :stringio_read, :sysread
@@ -32,6 +33,10 @@ describe "StringIO#sysread when passed nil" do
   end
 end
 
+describe "StringIO#sysread when passed length" do
+  it_behaves_like :stringio_sysread_length, :sysread
+end
+
 describe "StringIO#sysread when passed [length]" do
   before :each do
     @io = StringIO.new("example")