1 files changed, 1081 insertions, 11 deletions

diff --git a/test/stringio/test_stringio.rb b/test/stringio/test_stringio.rb
index de15ab5508..024906261e 100644
--- a/test/stringio/test_stringio.rb
+++ b/test/stringio/test_stringio.rb
@@ -1,9 +1,8 @@
+# frozen_string_literal: false
 require 'test/unit'
 require 'stringio'
-dir = File.expand_path(__FILE__)
-2.times {dir = File.dirname(dir)}
-$:.replace([File.join(dir, "ruby")] | $:)
-require 'ut_eof'
+require "rbconfig/sizeof"
+require_relative '../ruby/ut_eof'
 
 class TestStringIO < Test::Unit::TestCase
   include TestEOF
@@ -15,29 +14,1100 @@ class TestStringIO < Test::Unit::TestCase
 
   include TestEOF::Seek
 
-  def test_truncate # [ruby-dev:24190]
+  def test_do_not_mutate_shared_buffers
+    # Ensure we have two strings that are not embedded but have the same shared
+    # string reference.
+    #
+    # In this case, we must use eval because we need two strings literals that
+    # are long enough they cannot be embedded, but also contain the same bytes.
+
+    a = eval("+"+("x" * 1024).dump)
+    b = eval("+"+("x" * 1024).dump)
+
+    s = StringIO.new(b)
+    s.getc
+    s.ungetc '#'
+
+    # We mutated b, so a should not be mutated
+    assert_equal("x", a[0])
+  end
+
+  def test_version
+    assert_kind_of(String, StringIO::VERSION)
+  end
+
+  def test_initialize
+    assert_kind_of StringIO, StringIO.new
+    assert_kind_of StringIO, StringIO.new('str')
+    assert_kind_of StringIO, StringIO.new('str', 'r+')
+    assert_kind_of StringIO, StringIO.new(nil)
+    assert_raise(ArgumentError) { StringIO.new('', 'x') }
+    assert_raise(ArgumentError) { StringIO.new('', 'rx') }
+    assert_raise(ArgumentError) { StringIO.new('', 'rbt') }
+    assert_raise(TypeError) { StringIO.new(Object) }
+
+    o = Object.new
+    def o.to_str
+      nil
+    end
+    assert_raise(TypeError) { StringIO.new(o) }
+
+    o = Object.new
+    def o.to_str
+      'str'
+    end
+    assert_kind_of StringIO, StringIO.new(o)
+  end
+
+  def test_null
+    io = StringIO.new(nil)
+    assert_nil io.gets
+    io.puts "abc"
+    assert_nil io.string
+
+    # Null device StringIO just drop ungot string
+    io.ungetc '#'
+    assert_nil io.getc
+  end
+
+  def test_eof_null
+    io = StringIO.new(nil)
+    assert_predicate io, :eof?
+  end
+
+  def test_pread_null
+    io = StringIO.new(nil)
+    assert_raise(EOFError) { io.pread(1, 0) }
+  end
+
+  def test_read_null
+    io = StringIO.new(nil)
+    assert_equal "", io.read(0)
+  end
+
+  def test_seek_null
+    io = StringIO.new(nil)
+    assert_equal(0, io.seek(0, IO::SEEK_SET))
+    assert_equal(0, io.pos)
+    assert_equal(0, io.seek(0, IO::SEEK_CUR))
+    assert_equal(0, io.pos)
+    assert_equal(0, io.seek(0, IO::SEEK_END))  # This should not segfault
+    assert_equal(0, io.pos)
+  end
+
+  def test_truncate
     io = StringIO.new("")
     io.puts "abc"
-    io.truncate(0)
+    assert_equal(0, io.truncate(0))
     io.puts "def"
-    assert_equal("\0\0\0\0def\n", io.string)
+    assert_equal("\0\0\0\0def\n", io.string, "[ruby-dev:24190]")
+    assert_raise(Errno::EINVAL) { io.truncate(-1) }
+    assert_equal(0, io.truncate(10))
+    assert_equal("\0\0\0\0def\n\0\0", io.string)
   end
 
-  def test_seek_beyond_eof # [ruby-dev:24194]
+  def test_seek_beyond_eof
     io = StringIO.new
     n = 100
     io.seek(n)
     io.print "last"
-    assert_equal("\0" * n + "last", io.string)
+    assert_equal("\0" * n + "last", io.string, "[ruby-dev:24194]")
   end
 
-  def test_overwrite # [ruby-core:03836]
+  def test_overwrite
     stringio = StringIO.new
     responses = ['', 'just another ruby', 'hacker']
     responses.each do |resp|
       stringio.puts(resp)
       stringio.rewind
     end
-    assert_equal("hacker\nother ruby\n", stringio.string)
+    assert_equal("hacker\nother ruby\n", stringio.string, "[ruby-core:3836]")
+  end
+
+  def test_gets
+    assert_equal(nil, StringIO.new("").gets)
+    assert_equal("\n", StringIO.new("\n").gets)
+    assert_equal("a\n", StringIO.new("a\n").gets)
+    assert_equal("a\n", StringIO.new("a\nb\n").gets)
+    assert_equal("a", StringIO.new("a").gets)
+    assert_equal("a\n", StringIO.new("a\nb").gets)
+    assert_equal("abc\n", StringIO.new("abc\n\ndef\n").gets)
+    assert_equal("abc\n\ndef\n", StringIO.new("abc\n\ndef\n").gets(nil))
+    assert_equal("abc\n\n", StringIO.new("abc\n\ndef\n").gets(""))
+    stringio = StringIO.new("abc\n\ndef\n")
+    assert_equal("abc\n\n", stringio.gets(""))
+    assert_equal("def\n", stringio.gets(""))
+    assert_raise(TypeError){StringIO.new("").gets(1, 1)}
+    assert_nothing_raised {StringIO.new("").gets(nil, nil)}
+
+    assert_string("", Encoding::UTF_8, StringIO.new("foo").gets(0))
+  end
+
+  def test_gets_utf_16
+    stringio = StringIO.new("line1\nline2\nline3\n".encode("utf-16le"))
+    assert_equal("line1\n".encode("utf-16le"), stringio.gets)
+    assert_equal("line2\n".encode("utf-16le"), stringio.gets)
+    assert_equal("line3\n".encode("utf-16le"), stringio.gets)
+    assert_nil(stringio.gets)
+  end
+
+  def test_gets_chomp
+    assert_equal(nil, StringIO.new("").gets(chomp: true))
+    assert_equal("", StringIO.new("\n").gets(chomp: true))
+    assert_equal("a", StringIO.new("a\n").gets(chomp: true))
+    assert_equal("a", StringIO.new("a\nb\n").gets(chomp: true))
+    assert_equal("a", StringIO.new("a").gets(chomp: true))
+    assert_equal("a", StringIO.new("a\nb").gets(chomp: true))
+    assert_equal("abc", StringIO.new("abc\n\ndef\n").gets(chomp: true))
+    assert_equal("abc\n\ndef\n", StringIO.new("abc\n\ndef\n").gets(nil, chomp: true))
+    assert_equal("abc", StringIO.new("abc\n\ndef\n").gets("", chomp: true))
+    stringio = StringIO.new("abc\n\ndef\n")
+    assert_equal("abc", stringio.gets("", chomp: true))
+    assert_equal("def\n", stringio.gets("", chomp: true))
+
+    assert_string("", Encoding::UTF_8, StringIO.new("\n").gets(chomp: true))
+
+    assert_equal("", StringIO.new("ab").gets("ab", chomp: true))
+  end
+
+  def test_gets_chomp_eol
+    assert_equal(nil, StringIO.new("").gets(chomp: true))
+    assert_equal("", StringIO.new("\r\n").gets(chomp: true))
+    assert_equal("a", StringIO.new("a\r\n").gets(chomp: true))
+    assert_equal("a", StringIO.new("a\r\nb\r\n").gets(chomp: true))
+    assert_equal("a", StringIO.new("a").gets(chomp: true))
+    assert_equal("a", StringIO.new("a\r\nb").gets(chomp: true))
+    assert_equal("abc", StringIO.new("abc\r\n\r\ndef\r\n").gets(chomp: true))
+    assert_equal("abc\r\n\r\ndef\r\n", StringIO.new("abc\r\n\r\ndef\r\n").gets(nil, chomp: true))
+    assert_equal("abc", StringIO.new("abc\r\n\r\ndef\r\n").gets("", chomp: true))
+    stringio = StringIO.new("abc\r\n\r\ndef\r\n")
+    assert_equal("abc", stringio.gets("", chomp: true))
+    assert_equal("def\r\n", stringio.gets("", chomp: true))
+  end
+
+  def test_readlines
+    assert_equal([], StringIO.new("").readlines)
+    assert_equal(["\n"], StringIO.new("\n").readlines)
+    assert_equal(["a\n"], StringIO.new("a\n").readlines)
+    assert_equal(["a\n", "b\n"], StringIO.new("a\nb\n").readlines)
+    assert_equal(["a"], StringIO.new("a").readlines)
+    assert_equal(["a\n", "b"], StringIO.new("a\nb").readlines)
+    assert_equal(["abc\n", "\n", "def\n"], StringIO.new("abc\n\ndef\n").readlines)
+    assert_equal(["abc\n\ndef\n"], StringIO.new("abc\n\ndef\n").readlines(nil), "[ruby-dev:34591]")
+    assert_equal(["abc\n\n", "def\n"], StringIO.new("abc\n\ndef\n").readlines(""))
+  end
+
+  def test_write
+    s = ""
+    f = StringIO.new(s, "w")
+    f.print("foo")
+    f.close
+    assert_equal("foo", s)
+
+    f = StringIO.new(s, File::WRONLY)
+    f.print("bar")
+    f.close
+    assert_equal("bar", s)
+
+    f = StringIO.new(s, "a")
+    o = Object.new
+    def o.to_s; "baz"; end
+    f.print(o)
+    f.close
+    assert_equal("barbaz", s)
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_write_nonblock_no_exceptions
+    s = ""
+    f = StringIO.new(s, "w")
+    f.write_nonblock("foo", exception: false)
+    f.close
+    assert_equal("foo", s)
+  end
+
+  def test_write_nonblock
+    s = ""
+    f = StringIO.new(s, "w")
+    f.write_nonblock("foo")
+    f.close
+    assert_equal("foo", s)
+
+    f = StringIO.new(s, File::WRONLY)
+    f.write_nonblock("bar")
+    f.close
+    assert_equal("bar", s)
+
+    f = StringIO.new(s, "a")
+    o = Object.new
+    def o.to_s; "baz"; end
+    f.write_nonblock(o)
+    f.close
+    assert_equal("barbaz", s)
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_write_encoding
+    s = "".force_encoding(Encoding::UTF_8)
+    f = StringIO.new(s)
+    f.print("\u{3053 3093 306b 3061 306f ff01}".b)
+    assert_equal(Encoding::UTF_8, s.encoding, "honor the original encoding over ASCII-8BIT")
+  end
+
+  def test_write_encoding_conversion
+    convertible = "\u{3042}"
+    inconvertible = "\u{1f363}"
+    conversion_encoding = Encoding::Windows_31J
+
+    s = StringIO.new.set_encoding(conversion_encoding)
+    s.write(convertible)
+    assert_equal(conversion_encoding, s.string.encoding)
+
+    s = StringIO.new.set_encoding(Encoding::UTF_8)
+    s.write("foo".force_encoding("ISO-8859-1"), convertible)
+    assert_equal(Encoding::UTF_8, s.string.encoding)
+
+    s = StringIO.new.set_encoding(Encoding::US_ASCII)
+    s.write("foo".force_encoding("US-ASCII"), convertible)
+    assert_equal(Encoding::UTF_8, s.string.encoding)
+
+    all_assertions do |a|
+      [
+        inconvertible,
+        convertible + inconvertible,
+        [convertible, inconvertible],
+        ["a", inconvertible],
+      ].each do |data|
+        a.for(data.inspect) do
+          s = StringIO.new.set_encoding(conversion_encoding)
+          assert_raise(Encoding::CompatibilityError) do
+            s.write(*data)
+          end
+        end
+      end
+    end
+  end
+
+  def test_write_integer_overflow
+    f = StringIO.new
+    f.pos = StringIO::MAX_LENGTH
+    assert_raise(ArgumentError) {
+      f.write("pos + len overflows")
+    }
+  end
+
+  def test_write_with_multiple_arguments
+    s = ""
+    f = StringIO.new(s, "w")
+    f.write("foo", "bar")
+    f.close
+    assert_equal("foobar", s)
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_set_encoding
+    bug10285 = '[ruby-core:65240] [Bug #10285]'
+    f = StringIO.new()
+    f.set_encoding(Encoding::ASCII_8BIT)
+    f.write("quz \x83 mat".b)
+    s = "foo \x97 bar".force_encoding(Encoding::WINDOWS_1252)
+    assert_nothing_raised(Encoding::CompatibilityError, bug10285) {
+      f.write(s)
+    }
+    assert_equal(Encoding::ASCII_8BIT, f.string.encoding, bug10285)
+
+    bug11827 = '[ruby-core:72189] [Bug #11827]'
+    f = StringIO.new("foo\x83".freeze)
+    assert_nothing_raised(RuntimeError, bug11827) {
+      f.set_encoding(Encoding::ASCII_8BIT)
+    }
+    assert_equal("foo\x83".b, f.gets)
+
+    f = StringIO.new()
+    f.set_encoding("ISO-8859-16:ISO-8859-1")
+    assert_equal(Encoding::ISO_8859_16, f.external_encoding)
+    assert_equal(Encoding::ISO_8859_16, f.string.encoding)
+    assert_nil(f.internal_encoding)
+  end
+
+  def test_mode_error
+    f = StringIO.new("", "r")
+    assert_raise(IOError) { f.write("foo") }
+
+    f = StringIO.new("", "w")
+    assert_raise(IOError) { f.read }
+
+    assert_raise(Errno::EACCES) { StringIO.new("".freeze, "w") }
+    s = ""
+    f = StringIO.new(s, "w")
+    s.freeze
+    assert_raise(IOError) { f.write("foo") }
+
+    assert_raise(IOError) { StringIO.allocate.read }
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_open
+    s = ""
+    StringIO.open("foo") {|f| s = f.read }
+    assert_equal("foo", s)
+  end
+
+  def test_isatty
+    assert_equal(false, StringIO.new("").isatty)
+  end
+
+  def test_fsync
+    assert_equal(0, StringIO.new("").fsync)
+  end
+
+  def test_sync
+    assert_equal(true, StringIO.new("").sync)
+    assert_equal(false, StringIO.new("").sync = false)
+  end
+
+  def test_set_fcntl
+    assert_raise(NotImplementedError) { StringIO.new("").fcntl }
+  end
+
+  def test_close
+    f = StringIO.new("")
+    f.close
+    assert_nil(f.close)
+
+    f = StringIO.new("")
+    f.close_read
+    f.close_write
+    assert_nil(f.close)
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_close_read
+    f = StringIO.new("")
+    f.close_read
+    assert_raise(IOError) { f.read }
+    assert_nothing_raised(IOError) {f.close_read}
+    f.close
+
+    f = StringIO.new("", "w")
+    assert_raise(IOError) { f.close_read }
+    f.close
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_close_write
+    f = StringIO.new("")
+    f.close_write
+    assert_raise(IOError) { f.write("foo") }
+    assert_nothing_raised(IOError) {f.close_write}
+    f.close
+
+    f = StringIO.new("", "r")
+    assert_raise(IOError) { f.close_write }
+    f.close
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_closed
+    f = StringIO.new("")
+    assert_equal(false, f.closed?)
+    f.close
+    assert_equal(true, f.closed?)
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_closed_read
+    f = StringIO.new("")
+    assert_equal(false, f.closed_read?)
+    f.close_write
+    assert_equal(false, f.closed_read?)
+    f.close_read
+    assert_equal(true, f.closed_read?)
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_closed_write
+    f = StringIO.new("")
+    assert_equal(false, f.closed_write?)
+    f.close_read
+    assert_equal(false, f.closed_write?)
+    f.close_write
+    assert_equal(true, f.closed_write?)
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_dup
+    f1 = StringIO.new("1234")
+    assert_equal("1", f1.getc)
+    f2 = f1.dup
+    assert_equal("2", f2.getc)
+    assert_equal("3", f1.getc)
+    assert_equal("4", f2.getc)
+    assert_equal(nil, f1.getc)
+    assert_equal(true, f2.eof?)
+    f1.close
+    assert_equal(false, f2.closed?, '[ruby-core:48443]')
+  ensure
+    f1.close unless f1.closed?
+    f2.close unless f2.closed?
+  end
+
+  def test_lineno
+    f = StringIO.new("foo\nbar\nbaz\n")
+    assert_equal([0, "foo\n"], [f.lineno, f.gets])
+    assert_equal([1, "bar\n"], [f.lineno, f.gets])
+    f.lineno = 1000
+    assert_equal([1000, "baz\n"], [f.lineno, f.gets])
+    assert_equal([1001, nil], [f.lineno, f.gets])
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_pos
+    f = StringIO.new("foo\nbar\nbaz\n")
+    assert_equal([0, "foo\n"], [f.pos, f.gets])
+    assert_equal([4, "bar\n"], [f.pos, f.gets])
+    assert_raise(Errno::EINVAL) { f.pos = -1 }
+    f.pos = 1
+    assert_equal([1, "oo\n"], [f.pos, f.gets])
+    assert_equal([4, "bar\n"], [f.pos, f.gets])
+    assert_equal([8, "baz\n"], [f.pos, f.gets])
+    assert_equal([12, nil], [f.pos, f.gets])
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_reopen
+    f = StringIO.new("foo\nbar\nbaz\n")
+    assert_equal("foo\n", f.gets)
+    f.reopen("qux\nquux\nquuux\n")
+    assert_equal("qux\n", f.gets)
+
+    f2 = StringIO.new("")
+    f2.reopen(f)
+    assert_equal("quux\n", f2.gets)
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_seek
+    f = StringIO.new("1234")
+    assert_raise(Errno::EINVAL) { f.seek(-1) }
+    f.seek(-1, 2)
+    assert_equal("4", f.getc)
+    assert_raise(Errno::EINVAL) { f.seek(1, 3) }
+    f.close
+    assert_raise(IOError) { f.seek(0) }
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_seek_frozen_string
+    f = StringIO.new(-"1234")
+    assert_equal(0, f.seek(1))
+  end
+
+  def test_each_byte
+    f = StringIO.new("1234")
+    a = []
+    f.each_byte {|c| a << c }
+    assert_equal(%w(1 2 3 4).map {|c| c.ord }, a)
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_each_byte_closed
+    f = StringIO.new("1234")
+    assert_equal("1".ord, f.each_byte {|c| f.close; break c })
+    f = StringIO.new("1234")
+    assert_raise(IOError) do
+      f.each_byte { f.close }
+    end
+  end
+
+  def test_getbyte
+    f = StringIO.new("1234")
+    assert_equal("1".ord, f.getbyte)
+    assert_equal("2".ord, f.getbyte)
+    assert_equal("3".ord, f.getbyte)
+    assert_equal("4".ord, f.getbyte)
+    assert_equal(nil, f.getbyte)
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_ungetbyte
+    s = "foo\nbar\n"
+    t = StringIO.new(s, "r")
+    t.ungetbyte(0x41)
+    assert_equal(0x41, t.getbyte)
+    t.ungetbyte("qux")
+    assert_equal("quxfoo\n", t.gets)
+    t.set_encoding("utf-8")
+    t.ungetbyte(0x89)
+    t.ungetbyte(0x8e)
+    t.ungetbyte("\xe7")
+    t.ungetbyte("\xe7\xb4\x85")
+    assert_equal("\u7d05\u7389bar\n", t.gets)
+    assert_equal("q\u7d05\u7389bar\n", s)
+    t.pos = 1
+    t.ungetbyte("\u{30eb 30d3 30fc}")
+    assert_equal(0, t.pos)
+    assert_equal("\u{30eb 30d3 30fc}\u7d05\u7389bar\n", s)
+
+    assert_nothing_raised {t.ungetbyte(-1)}
+    assert_nothing_raised {t.ungetbyte(256)}
+    assert_nothing_raised {t.ungetbyte(1<<64)}
+  end
+
+  def test_ungetc
+    s = "1234"
+    f = StringIO.new(s, "r")
+    assert_nothing_raised { f.ungetc("x") }
+    assert_equal("x", f.getc) # bug? -> it's a feature from 1.9.
+    assert_equal("1", f.getc)
+
+    s = "1234"
+    f = StringIO.new(s, "r")
+    assert_equal("1", f.getc)
+    f.ungetc("y".ord)
+    assert_equal("y", f.getc)
+    assert_equal("2", f.getc)
+
+    assert_raise(RangeError) {f.ungetc(0x1ffffff)}
+    assert_raise(RangeError) {f.ungetc(0xffffffffffffff)}
+  ensure
+    f.close unless f.closed?
+  end
+
+  def test_readchar
+    f = StringIO.new("1234")
+    a = ""
+    assert_raise(EOFError) { loop { a << f.readchar } }
+    assert_equal("1234", a)
+  end
+
+  def test_readbyte
+    f = StringIO.new("1234")
+    a = []
+    assert_raise(EOFError) { loop { a << f.readbyte } }
+    assert_equal("1234".unpack("C*"), a)
+  end
+
+  def test_each_char
+    f = StringIO.new("1234")
+    assert_equal(%w(1 2 3 4), f.each_char.to_a)
+  end
+
+  def test_each_char_closed
+    f = StringIO.new("1234")
+    assert_equal("1", f.each_char {|c| f.close; break c })
+    f = StringIO.new("1234")
+    assert_raise(IOError) do
+      f.each_char { f.close }
+    end
+  end
+
+  def test_each_codepoint
+    f = StringIO.new("1234")
+    assert_equal([49, 50, 51, 52], f.each_codepoint.to_a)
+  end
+
+  def test_each_codepoint_closed
+    f = StringIO.new("1234")
+    assert_equal("1".ord, f.each_codepoint {|c| f.close; break c })
+    f = StringIO.new("1234")
+    assert_raise(IOError) do
+      f.each_codepoint { f.close }
+    end
+  end
+
+  def test_each_codepoint_enumerator
+    io = StringIO.new('你好построить')
+
+    chinese_part = io.each_codepoint.take(2).pack('U*')
+    russian_part = io.read(40).force_encoding('UTF-8')
+
+    assert_equal("你好", chinese_part)
+    assert_equal("построить", russian_part)
+  end
+
+  def test_gets2
+    f = StringIO.new("foo\nbar\nbaz\n")
+    assert_equal("fo", f.gets(2))
+
+    o = Object.new
+    def o.to_str; "z"; end
+    assert_equal("o\nbar\nbaz", f.gets(o))
+
+    f = StringIO.new("foo\nbar\nbaz\n")
+    assert_equal("foo\nbar\nbaz", f.gets("az"))
+    f = StringIO.new("a" * 10000 + "zz!")
+    assert_equal("a" * 10000 + "zz", f.gets("zz"))
+    f = StringIO.new("a" * 10000 + "zz!")
+    assert_equal("a" * 10000 + "zz!", f.gets("zzz"))
+
+    bug4112 = '[ruby-dev:42674]'
+    ["a".encode("utf-16be"), "\u3042"].each do |s|
+      assert_equal(s, StringIO.new(s).gets(1), bug4112)
+      assert_equal(s, StringIO.new(s).gets(nil, 1), bug4112)
+    end
+  end
+
+  def test_each_string_sep
+    f = StringIO.new('a||b||c')
+    assert_equal(["a||", "b||", "c"], f.each("||").to_a)
+    f.rewind
+    assert_equal(["a", "b", "c"], f.each("||", chomp: true).to_a)
+  end
+
+  def test_each
+    f = StringIO.new("foo\nbar\nbaz\n")
+    assert_equal(["foo\n", "bar\n", "baz\n"], f.each.to_a)
+    f.rewind
+    assert_equal(["foo", "bar", "baz"], f.each(chomp: true).to_a)
+    f = StringIO.new("foo\nbar\n\n\nbaz\n")
+    assert_equal(["foo\nbar\n\n\n", "baz\n"], f.each("").to_a)
+    f.rewind
+    assert_equal(["foo\nbar", "baz\n"], f.each("", chomp: true).to_a)
+
+    f = StringIO.new("foo\r\nbar\r\n\r\n\r\nbaz\r\n")
+    assert_equal(["foo\r\nbar\r\n\r\n\r\n", "baz\r\n"], f.each("").to_a)
+    f.rewind
+    assert_equal(["foo\r\nbar", "baz\r\n"], f.each("", chomp: true).to_a)
+
+    f = StringIO.new("abc\n\ndef\n")
+    assert_equal(["ab", "c\n", "\nd", "ef", "\n"], f.each(nil, 2, chomp: true).to_a)
+  end
+
+  def test_putc
+    s = ""
+    f = StringIO.new(s, "w")
+    f.putc("1")
+    f.putc("2")
+    f.putc("3")
+    f.close
+    assert_equal("123", s)
+
+    s = "foo"
+    f = StringIO.new(s, "a")
+    f.putc("1")
+    f.putc("2")
+    f.putc("3")
+    f.close
+    assert_equal("foo123", s)
+  end
+
+  def test_putc_nonascii
+    s = ""
+    f = StringIO.new(s, "w")
+    f.putc("\u{3042}")
+    f.putc(0x3044)
+    f.close
+    assert_equal("\u{3042}D", s)
+
+    s = "foo"
+    f = StringIO.new(s, "a")
+    f.putc("\u{3042}")
+    f.putc(0x3044)
+    f.close
+    assert_equal("foo\u{3042}D", s)
+  end
+
+  def test_read
+    f = StringIO.new("\u3042\u3044")
+    assert_raise(ArgumentError) { f.read(-1) }
+    assert_raise(ArgumentError) { f.read(1, 2, 3) }
+    assert_equal("\u3042\u3044", f.read)
+    assert_nil(f.read(1))
+    f.rewind
+    assert_equal("\u3042\u3044".force_encoding(Encoding::ASCII_8BIT), f.read(f.size))
+
+    bug5207 = '[ruby-core:39026]'
+    f.rewind
+    assert_equal("\u3042\u3044", f.read(nil, nil), bug5207)
+    f.rewind
+    s = ""
+    assert_same(s, f.read(nil, s))
+    assert_equal("\u3042\u3044", s, bug5207)
+    f.rewind
+    # not empty buffer
+    s = "0123456789"
+    assert_same(s, f.read(nil, s))
+    assert_equal("\u3042\u3044", s)
+
+    bug13806 = '[ruby-core:82349] [Bug #13806]'
+    assert_string("", Encoding::UTF_8, f.read, bug13806)
+    assert_string("", Encoding::UTF_8, f.read(nil, nil), bug13806)
+    s.force_encoding(Encoding::US_ASCII)
+    assert_same(s, f.read(nil, s))
+    assert_string("", Encoding::UTF_8, s, bug13806)
+
+    bug20418 = '[Bug #20418] ™€®'.b
+    f = StringIO.new(bug20418)
+    s = ""
+    assert_equal(Encoding::UTF_8, s.encoding, bug20418)
+    f.read(4, s)
+    assert_equal(Encoding::UTF_8, s.encoding, bug20418)
+
+    f.rewind
+    s = ""
+    f.read(nil, s)
+    assert_equal(Encoding::ASCII_8BIT, s.encoding, bug20418)
+  end
+
+  def test_readpartial
+    f = StringIO.new("\u3042\u3044")
+    assert_raise(ArgumentError) { f.readpartial(-1) }
+    assert_raise(ArgumentError) { f.readpartial(1, 2, 3) }
+    assert_equal("\u3042\u3044".force_encoding(Encoding::ASCII_8BIT), f.readpartial(100))
+    f.rewind
+    assert_equal("\u3042\u3044".force_encoding(Encoding::ASCII_8BIT), f.readpartial(f.size))
+    f.rewind
+    # not empty buffer
+    s = '0123456789'.b
+    assert_equal("\u3042\u3044".b, f.readpartial(f.size, s))
+  end
+
+  def test_read_nonblock
+    f = StringIO.new("\u3042\u3044")
+    assert_raise(ArgumentError) { f.read_nonblock(-1) }
+    assert_raise(ArgumentError) { f.read_nonblock(1, 2, 3) }
+    assert_equal("\u3042\u3044".force_encoding("BINARY"), f.read_nonblock(100))
+    assert_raise(EOFError) { f.read_nonblock(10) }
+    f.rewind
+    assert_equal("\u3042\u3044".force_encoding(Encoding::ASCII_8BIT), f.read_nonblock(f.size))
+  end
+
+  def test_read_nonblock_no_exceptions
+    f = StringIO.new("\u3042\u3044")
+    assert_raise(ArgumentError) { f.read_nonblock(-1, exception: false) }
+    assert_raise(ArgumentError) { f.read_nonblock(1, 2, 3, exception: false) }
+    assert_raise(ArgumentError) { f.read_nonblock }
+    assert_equal("\u3042\u3044".force_encoding(Encoding::ASCII_8BIT), f.read_nonblock(100, exception: false))
+    assert_equal(nil, f.read_nonblock(10, exception: false))
+    f.rewind
+    assert_equal("\u3042\u3044".force_encoding(Encoding::ASCII_8BIT), f.read_nonblock(f.size))
+    f.rewind
+    # not empty buffer
+    s = '0123456789'.b
+    assert_equal("\u3042\u3044".b, f.read_nonblock(f.size, s))
+  end
+
+  def test_sysread
+    f = StringIO.new("sysread \u{30c6 30b9 30c8}")
+    assert_equal "sysread \u{30c6 30b9 30c8}", f.sysread
+    assert_equal "", f.sysread
+    assert_raise(EOFError) { f.sysread(1) }
+    f.rewind
+    assert_equal Encoding::ASCII_8BIT, f.sysread(3).encoding
+  end
+
+  def test_pread
+    f = StringIO.new("pread")
+    f.read
+
+    assert_equal "pre".b, f.pread(3, 0)
+    assert_equal "read".b, f.pread(4, 1)
+    assert_equal Encoding::ASCII_8BIT, f.pread(4, 1).encoding
+
+    buf = "".b
+    f.pread(3, 0, buf)
+    assert_equal "pre".b, buf
+    f.pread(4, 1, buf)
+    assert_equal "read".b, buf
+
+    assert_raise(EOFError) { f.pread(1, 5) }
+    assert_raise(ArgumentError) { f.pread(-1, 0) }
+    assert_raise(Errno::EINVAL) { f.pread(3, -1) }
+
+    assert_equal "".b, StringIO.new("").pread(0, 0)
+    assert_equal "".b, StringIO.new("").pread(0, -10)
+
+    buf = "stale".b
+    assert_equal "stale".b, StringIO.new("").pread(0, 0, buf)
+    assert_equal "stale".b, buf
+  end
+
+  def test_size
+    f = StringIO.new("1234")
+    assert_equal(4, f.size)
+  end
+
+  # This test is should in ruby/test_method.rb
+  # However this test depends on stringio library,
+  # we write it here.
+  class C < StringIO
+    alias old_init initialize
+    attr_reader :foo
+    def initialize
+      @foo = :ok
+      old_init
+    end
+  end
+
+  def test_method
+    assert_equal(:ok, C.new.foo, 'Bug #632 [ruby-core:19282]')
+  end
+
+  def test_ungetc_pos
+    b = '\\b00010001 \\B00010001 \\b1 \\B1 \\b000100011'
+    s = StringIO.new( b )
+    expected_pos = 0
+    while n = s.getc
+      assert_equal( expected_pos + 1, s.pos )
+
+      s.ungetc( n )
+      assert_equal( expected_pos, s.pos )
+      assert_equal( n, s.getc )
+
+      expected_pos += 1
+    end
+  end
+
+  def test_ungetc_padding
+    s = StringIO.new()
+    s.pos = 2
+    s.ungetc("a")
+    assert_equal("\0""a", s.string)
+    s.pos = 0
+    s.ungetc("b")
+    assert_equal("b""\0""a", s.string)
+  end
+
+  def test_ungetc_fill
+    count = 100
+    s = StringIO.new
+    s.print 'a' * count
+    s.ungetc('b' * (count * 5))
+    assert_equal((count * 5), s.string.size)
+    assert_match(/\Ab+\z/, s.string)
+  end
+
+  def test_ungetc_same_string
+    s = StringIO.new("abc" * 30)
+    s.ungetc(s.string)
+    assert_match(/\A(?:abc){60}\z/, s.string)
+
+    s = StringIO.new("abc" * 30)
+    s.pos = 70 # ("abc".size * 30 - 70).divmod(3) == [6, 2]
+    s.ungetc(s.string)
+    assert_match(/\A(?:abc){30}bc(?:abc){6}\z/, s.string)
+  end
+
+  def test_ungetbyte_pos
+    b = '\\b00010001 \\B00010001 \\b1 \\B1 \\b000100011'
+    s = StringIO.new( b )
+    expected_pos = 0
+    while n = s.getbyte
+      assert_equal( expected_pos + 1, s.pos )
+
+      s.ungetbyte( n )
+      assert_equal( expected_pos, s.pos )
+      assert_equal( n, s.getbyte )
+
+      expected_pos += 1
+    end
+  end
+
+  def test_ungetbyte_padding
+    s = StringIO.new()
+    s.pos = 2
+    s.ungetbyte("a".ord)
+    assert_equal("\0""a", s.string)
+    s.pos = 0
+    s.ungetbyte("b".ord)
+    assert_equal("b""\0""a", s.string)
+  end
+
+  def test_ungetbyte_fill
+    count = 100
+    s = StringIO.new
+    s.print 'a' * count
+    s.ungetbyte('b' * (count * 5))
+    assert_equal((count * 5), s.string.size)
+    assert_match(/\Ab+\z/, s.string)
+  end
+
+  def test_ungetbyte_same_string
+    s = StringIO.new("abc" * 30)
+    s.ungetc(s.string)
+    assert_match(/\A(?:abc){60}\z/, s.string)
+
+    s = StringIO.new("abc" * 30)
+    s.pos = 70 # ("abc".size * 30 - 70).divmod(3) == [6, 2]
+    s.ungetbyte(s.string)
+    assert_match(/\A(?:abc){30}bc(?:abc){6}\z/, s.string)
+  end
+
+  def test_frozen
+    s = StringIO.new
+    s.freeze
+    bug = '[ruby-core:33648]'
+    exception_class = defined?(FrozenError) ? FrozenError : RuntimeError
+    assert_raise(exception_class, bug) {s.puts("foo")}
+    assert_raise(exception_class, bug) {s.string = "foo"}
+    assert_raise(exception_class, bug) {s.reopen("")}
+  end
+
+  def test_frozen_string
+    s = StringIO.new("".freeze)
+    bug = '[ruby-core:48530]'
+    assert_raise(IOError, bug) {s.write("foo")}
+    assert_raise(IOError, bug) {s.ungetc("a")}
+    assert_raise(IOError, bug) {s.ungetbyte("a")}
+  end
+
+  def test_readlines_limit_0
+    assert_raise(ArgumentError, "[ruby-dev:43392]") { StringIO.new.readlines(0) }
+  end
+
+  def test_each_line_limit_0
+    assert_raise(ArgumentError, "[ruby-dev:43392]") { StringIO.new.each_line(0){} }
+    assert_raise(ArgumentError, "[ruby-dev:43392]") { StringIO.new.each_line("a",0){} }
+  end
+
+  def test_binmode
+    s = StringIO.new
+    s.set_encoding('utf-8')
+    assert_same s, s.binmode
+
+    bug_11945 = '[ruby-core:72699] [Bug #11945]'
+    assert_equal Encoding::ASCII_8BIT, s.external_encoding, bug_11945
+  end
+
+  def test_new_block_warning
+    assert_warn(/does not take block/) do
+      StringIO.new {}
+    end
+  end
+
+  def test_overflow
+    intptr_max = RbConfig::LIMITS["INTPTR_MAX"]
+    return if intptr_max > StringIO::MAX_LENGTH
+    limit = intptr_max - 0x10
+    assert_separately(%w[-W0 -rstringio], "#{<<-"begin;"}\n#{<<-"end;"}")
+    begin;
+      limit = #{limit}
+      ary = []
+      begin
+        x = "a"*0x100000
+        break if [x].pack("p").unpack("i!")[0] < 0
+        ary << x
+      end while ary.size <= 100
+      s = StringIO.new(x)
+      s.gets("xxx", limit)
+      assert_equal(0x100000, s.pos)
+    end;
+  end
+
+  def test_encoding_write
+    s = StringIO.new("", "w:utf-32be")
+    s.print "abc"
+    assert_equal("abc".encode("utf-32be"), s.string)
+  end
+
+  def test_encoding_read
+    s = StringIO.new("abc".encode("utf-32be"), "r:utf-8")
+    assert_equal("\0\0\0a\0\0\0b\0\0\0c", s.read)
+  end
+
+  %w/UTF-8 UTF-16BE UTF-16LE UTF-32BE UTF-32LE/.each do |name|
+    define_method("test_strip_bom:#{name}") do
+      text = "\uFEFF\u0100a"
+      content = text.encode(name)
+      result = StringIO.new(content, mode: 'rb:BOM|UTF-8').read
+      assert_equal(Encoding.find(name), result.encoding, name)
+      assert_equal(content[1..-1].b, result.b, name)
+
+      StringIO.open(content) {|f|
+        assert_equal(Encoding.find(name), f.set_encoding_by_bom)
+      }
+    end
+  end
+
+  def test_binary_encoding_read_and_default_internal
+    verbose, $VERBOSE = $VERBOSE, nil
+    default_internal = Encoding.default_internal
+    Encoding.default_internal = Encoding::UTF_8
+    $VERBOSE = verbose
+    assert_equal Encoding::BINARY, StringIO.new("Hello".b).read.encoding
+  ensure
+    $VERBOSE = nil
+    Encoding.default_internal = default_internal
+    $VERBOSE = verbose
+  end
+
+  def test_coderange_after_overwrite
+    s = StringIO.new("".b)
+
+    s.write("a=b&c=d")
+    s.rewind
+    assert_predicate(s.string, :ascii_only?)
+    s.write "\u{431 43e 433 443 441}"
+    assert_not_predicate(s.string, :ascii_only?)
+
+    s = StringIO.new("\u{3042}")
+    s.rewind
+    assert_not_predicate(s.string, :ascii_only?)
+    s.write('aaaa')
+    assert_predicate(s.string, :ascii_only?)
+  end
+
+  def test_coderange_after_read_into_buffer
+    s = StringIO.new("01234567890".b)
+
+    buf = "¿Cómo estás? Ça va bien?"
+    assert_not_predicate(buf, :ascii_only?)
+
+    assert_predicate(s.string, :ascii_only?)
+
+    s.read(10, buf)
+
+    assert_predicate(buf, :ascii_only?)
+    assert_equal '0123456789', buf
+  end
+
+  require "objspace"
+  if ObjectSpace.respond_to?(:dump) && ObjectSpace.dump(eval(%{"test"})).include?('"chilled":true') # Ruby 3.4+ chilled strings
+    def test_chilled_string
+      chilled_string = eval(%{""})
+      io = StringIO.new(chilled_string)
+      assert_warning(/literal string will be frozen/) { io << "test" }
+      assert_equal("test", io.string)
+      assert_same(chilled_string, io.string)
+    end
+
+    def test_chilled_string_string_set
+      io = StringIO.new
+      chilled_string = eval(%{""})
+      io.string = chilled_string
+      assert_warning(/literal string will be frozen/) { io << "test" }
+      assert_equal("test", io.string)
+      assert_same(chilled_string, io.string)
+    end
+
+    def test_chilled_string_set_enocoding
+      chilled_string = eval(%{""})
+      io = StringIO.new(chilled_string)
+      assert_warning("") { io.set_encoding(Encoding::BINARY) }
+      assert_same(chilled_string, io.string)
+    end
+  end
+
+  private
+
+  def assert_string(content, encoding, str, mesg = nil)
+    assert_equal([content, encoding], [str, str.encoding], mesg)
   end
 end