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Frank Wierzbicki committed 86c218f

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Lib/test/test_io.py

+"""Unit tests for the io module."""
+
+# Tests of io are scattered over the test suite:
+# * test_bufio - tests file buffering
+# * test_memoryio - tests BytesIO and StringIO
+# * test_fileio - tests FileIO
+# * test_file - tests the file interface
+# * test_io - tests everything else in the io module
+# * test_univnewlines - tests universal newline support
+# * test_largefile - tests operations on a file greater than 2**32 bytes
+#     (only enabled with -ulargefile)
+
+################################################################################
+# ATTENTION TEST WRITERS!!!
+################################################################################
+# When writing tests for io, it's important to test both the C and Python
+# implementations. This is usually done by writing a base test that refers to
+# the type it is testing as a attribute. Then it provides custom subclasses to
+# test both implementations. This file has lots of examples.
+################################################################################
+
+from __future__ import print_function
+from __future__ import unicode_literals
+
+import os
+import sys
+import time
+import array
+import random
+import unittest
+import weakref
+import abc
+import signal
+import errno
+from itertools import cycle, count
+from collections import deque
+from test import test_support as support
+
+import codecs
+import io  # C implementation of io
+import _pyio as pyio # Python implementation of io
+try:
+    import threading
+except ImportError:
+    threading = None
+try:
+    import fcntl
+except ImportError:
+    fcntl = None
+
+__metaclass__ = type
+bytes = support.py3k_bytes
+
+def _default_chunk_size():
+    """Get the default TextIOWrapper chunk size"""
+    with io.open(__file__, "r", encoding="latin1") as f:
+        return f._CHUNK_SIZE
+
+
+class MockRawIOWithoutRead:
+    """A RawIO implementation without read(), so as to exercise the default
+    RawIO.read() which calls readinto()."""
+
+    def __init__(self, read_stack=()):
+        self._read_stack = list(read_stack)
+        self._write_stack = []
+        self._reads = 0
+        self._extraneous_reads = 0
+
+    def write(self, b):
+        self._write_stack.append(bytes(b))
+        return len(b)
+
+    def writable(self):
+        return True
+
+    def fileno(self):
+        return 42
+
+    def readable(self):
+        return True
+
+    def seekable(self):
+        return True
+
+    def seek(self, pos, whence):
+        return 0   # wrong but we gotta return something
+
+    def tell(self):
+        return 0   # same comment as above
+
+    def readinto(self, buf):
+        self._reads += 1
+        max_len = len(buf)
+        try:
+            data = self._read_stack[0]
+        except IndexError:
+            self._extraneous_reads += 1
+            return 0
+        if data is None:
+            del self._read_stack[0]
+            return None
+        n = len(data)
+        if len(data) <= max_len:
+            del self._read_stack[0]
+            buf[:n] = data
+            return n
+        else:
+            buf[:] = data[:max_len]
+            self._read_stack[0] = data[max_len:]
+            return max_len
+
+    def truncate(self, pos=None):
+        return pos
+
+class CMockRawIOWithoutRead(MockRawIOWithoutRead, io.RawIOBase):
+    pass
+
+class PyMockRawIOWithoutRead(MockRawIOWithoutRead, pyio.RawIOBase):
+    pass
+
+
+class MockRawIO(MockRawIOWithoutRead):
+
+    def read(self, n=None):
+        self._reads += 1
+        try:
+            return self._read_stack.pop(0)
+        except:
+            self._extraneous_reads += 1
+            return b""
+
+class CMockRawIO(MockRawIO, io.RawIOBase):
+    pass
+
+class PyMockRawIO(MockRawIO, pyio.RawIOBase):
+    pass
+
+
+class MisbehavedRawIO(MockRawIO):
+    def write(self, b):
+        return MockRawIO.write(self, b) * 2
+
+    def read(self, n=None):
+        return MockRawIO.read(self, n) * 2
+
+    def seek(self, pos, whence):
+        return -123
+
+    def tell(self):
+        return -456
+
+    def readinto(self, buf):
+        MockRawIO.readinto(self, buf)
+        return len(buf) * 5
+
+class CMisbehavedRawIO(MisbehavedRawIO, io.RawIOBase):
+    pass
+
+class PyMisbehavedRawIO(MisbehavedRawIO, pyio.RawIOBase):
+    pass
+
+
+class CloseFailureIO(MockRawIO):
+    closed = 0
+
+    def close(self):
+        if not self.closed:
+            self.closed = 1
+            raise IOError
+
+class CCloseFailureIO(CloseFailureIO, io.RawIOBase):
+    pass
+
+class PyCloseFailureIO(CloseFailureIO, pyio.RawIOBase):
+    pass
+
+
+class MockFileIO:
+
+    def __init__(self, data):
+        self.read_history = []
+        super(MockFileIO, self).__init__(data)
+
+    def read(self, n=None):
+        res = super(MockFileIO, self).read(n)
+        self.read_history.append(None if res is None else len(res))
+        return res
+
+    def readinto(self, b):
+        res = super(MockFileIO, self).readinto(b)
+        self.read_history.append(res)
+        return res
+
+class CMockFileIO(MockFileIO, io.BytesIO):
+    pass
+
+class PyMockFileIO(MockFileIO, pyio.BytesIO):
+    pass
+
+
+class MockNonBlockWriterIO:
+
+    def __init__(self):
+        self._write_stack = []
+        self._blocker_char = None
+
+    def pop_written(self):
+        s = b"".join(self._write_stack)
+        self._write_stack[:] = []
+        return s
+
+    def block_on(self, char):
+        """Block when a given char is encountered."""
+        self._blocker_char = char
+
+    def readable(self):
+        return True
+
+    def seekable(self):
+        return True
+
+    def writable(self):
+        return True
+
+    def write(self, b):
+        b = bytes(b)
+        n = -1
+        if self._blocker_char:
+            try:
+                n = b.index(self._blocker_char)
+            except ValueError:
+                pass
+            else:
+                if n > 0:
+                    # write data up to the first blocker
+                    self._write_stack.append(b[:n])
+                    return n
+                else:
+                    # cancel blocker and indicate would block
+                    self._blocker_char = None
+                    return None
+        self._write_stack.append(b)
+        return len(b)
+
+class CMockNonBlockWriterIO(MockNonBlockWriterIO, io.RawIOBase):
+    BlockingIOError = io.BlockingIOError
+
+class PyMockNonBlockWriterIO(MockNonBlockWriterIO, pyio.RawIOBase):
+    BlockingIOError = pyio.BlockingIOError
+
+
+class IOTest(unittest.TestCase):
+
+    def setUp(self):
+        support.unlink(support.TESTFN)
+
+    def tearDown(self):
+        support.unlink(support.TESTFN)
+
+    def write_ops(self, f):
+        self.assertEqual(f.write(b"blah."), 5)
+        f.truncate(0)
+        self.assertEqual(f.tell(), 5)
+        f.seek(0)
+
+        self.assertEqual(f.write(b"blah."), 5)
+        self.assertEqual(f.seek(0), 0)
+        self.assertEqual(f.write(b"Hello."), 6)
+        self.assertEqual(f.tell(), 6)
+        self.assertEqual(f.seek(-1, 1), 5)
+        self.assertEqual(f.tell(), 5)
+        self.assertEqual(f.write(bytearray(b" world\n\n\n")), 9)
+        self.assertEqual(f.seek(0), 0)
+        self.assertEqual(f.write(b"h"), 1)
+        self.assertEqual(f.seek(-1, 2), 13)
+        self.assertEqual(f.tell(), 13)
+
+        self.assertEqual(f.truncate(12), 12)
+        self.assertEqual(f.tell(), 13)
+        self.assertRaises(TypeError, f.seek, 0.0)
+
+    def read_ops(self, f, buffered=False):
+        data = f.read(5)
+        self.assertEqual(data, b"hello")
+        data = bytearray(data)
+        self.assertEqual(f.readinto(data), 5)
+        self.assertEqual(data, b" worl")
+        self.assertEqual(f.readinto(data), 2)
+        self.assertEqual(len(data), 5)
+        self.assertEqual(data[:2], b"d\n")
+        self.assertEqual(f.seek(0), 0)
+        self.assertEqual(f.read(20), b"hello world\n")
+        self.assertEqual(f.read(1), b"")
+        self.assertEqual(f.readinto(bytearray(b"x")), 0)
+        self.assertEqual(f.seek(-6, 2), 6)
+        self.assertEqual(f.read(5), b"world")
+        self.assertEqual(f.read(0), b"")
+        self.assertEqual(f.readinto(bytearray()), 0)
+        self.assertEqual(f.seek(-6, 1), 5)
+        self.assertEqual(f.read(5), b" worl")
+        self.assertEqual(f.tell(), 10)
+        self.assertRaises(TypeError, f.seek, 0.0)
+        if buffered:
+            f.seek(0)
+            self.assertEqual(f.read(), b"hello world\n")
+            f.seek(6)
+            self.assertEqual(f.read(), b"world\n")
+            self.assertEqual(f.read(), b"")
+
+    LARGE = 2**31
+
+    def large_file_ops(self, f):
+        assert f.readable()
+        assert f.writable()
+        self.assertEqual(f.seek(self.LARGE), self.LARGE)
+        self.assertEqual(f.tell(), self.LARGE)
+        self.assertEqual(f.write(b"xxx"), 3)
+        self.assertEqual(f.tell(), self.LARGE + 3)
+        self.assertEqual(f.seek(-1, 1), self.LARGE + 2)
+        self.assertEqual(f.truncate(), self.LARGE + 2)
+        self.assertEqual(f.tell(), self.LARGE + 2)
+        self.assertEqual(f.seek(0, 2), self.LARGE + 2)
+        self.assertEqual(f.truncate(self.LARGE + 1), self.LARGE + 1)
+        self.assertEqual(f.tell(), self.LARGE + 2)
+        self.assertEqual(f.seek(0, 2), self.LARGE + 1)
+        self.assertEqual(f.seek(-1, 2), self.LARGE)
+        self.assertEqual(f.read(2), b"x")
+
+    def test_invalid_operations(self):
+        # Try writing on a file opened in read mode and vice-versa.
+        for mode in ("w", "wb"):
+            with self.open(support.TESTFN, mode) as fp:
+                self.assertRaises(IOError, fp.read)
+                self.assertRaises(IOError, fp.readline)
+        with self.open(support.TESTFN, "rb") as fp:
+            self.assertRaises(IOError, fp.write, b"blah")
+            self.assertRaises(IOError, fp.writelines, [b"blah\n"])
+        with self.open(support.TESTFN, "r") as fp:
+            self.assertRaises(IOError, fp.write, "blah")
+            self.assertRaises(IOError, fp.writelines, ["blah\n"])
+
+    def test_raw_file_io(self):
+        with self.open(support.TESTFN, "wb", buffering=0) as f:
+            self.assertEqual(f.readable(), False)
+            self.assertEqual(f.writable(), True)
+            self.assertEqual(f.seekable(), True)
+            self.write_ops(f)
+        with self.open(support.TESTFN, "rb", buffering=0) as f:
+            self.assertEqual(f.readable(), True)
+            self.assertEqual(f.writable(), False)
+            self.assertEqual(f.seekable(), True)
+            self.read_ops(f)
+
+    def test_buffered_file_io(self):
+        with self.open(support.TESTFN, "wb") as f:
+            self.assertEqual(f.readable(), False)
+            self.assertEqual(f.writable(), True)
+            self.assertEqual(f.seekable(), True)
+            self.write_ops(f)
+        with self.open(support.TESTFN, "rb") as f:
+            self.assertEqual(f.readable(), True)
+            self.assertEqual(f.writable(), False)
+            self.assertEqual(f.seekable(), True)
+            self.read_ops(f, True)
+
+    def test_readline(self):
+        with self.open(support.TESTFN, "wb") as f:
+            f.write(b"abc\ndef\nxyzzy\nfoo\x00bar\nanother line")
+        with self.open(support.TESTFN, "rb") as f:
+            self.assertEqual(f.readline(), b"abc\n")
+            self.assertEqual(f.readline(10), b"def\n")
+            self.assertEqual(f.readline(2), b"xy")
+            self.assertEqual(f.readline(4), b"zzy\n")
+            self.assertEqual(f.readline(), b"foo\x00bar\n")
+            self.assertEqual(f.readline(None), b"another line")
+            self.assertRaises(TypeError, f.readline, 5.3)
+        with self.open(support.TESTFN, "r") as f:
+            self.assertRaises(TypeError, f.readline, 5.3)
+
+    def test_raw_bytes_io(self):
+        f = self.BytesIO()
+        self.write_ops(f)
+        data = f.getvalue()
+        self.assertEqual(data, b"hello world\n")
+        f = self.BytesIO(data)
+        self.read_ops(f, True)
+
+    def test_large_file_ops(self):
+        # On Windows and Mac OSX this test comsumes large resources; It takes
+        # a long time to build the >2GB file and takes >2GB of disk space
+        # therefore the resource must be enabled to run this test.
+        if sys.platform[:3] == 'win' or sys.platform == 'darwin':
+            if not support.is_resource_enabled("largefile"):
+                print("\nTesting large file ops skipped on %s." % sys.platform,
+                      file=sys.stderr)
+                print("It requires %d bytes and a long time." % self.LARGE,
+                      file=sys.stderr)
+                print("Use 'regrtest.py -u largefile test_io' to run it.",
+                      file=sys.stderr)
+                return
+        with self.open(support.TESTFN, "w+b", 0) as f:
+            self.large_file_ops(f)
+        with self.open(support.TESTFN, "w+b") as f:
+            self.large_file_ops(f)
+
+    def test_with_open(self):
+        for bufsize in (0, 1, 100):
+            f = None
+            with self.open(support.TESTFN, "wb", bufsize) as f:
+                f.write(b"xxx")
+            self.assertEqual(f.closed, True)
+            f = None
+            try:
+                with self.open(support.TESTFN, "wb", bufsize) as f:
+                    1 // 0
+            except ZeroDivisionError:
+                self.assertEqual(f.closed, True)
+            else:
+                self.fail("1 // 0 didn't raise an exception")
+
+    # issue 5008
+    def test_append_mode_tell(self):
+        with self.open(support.TESTFN, "wb") as f:
+            f.write(b"xxx")
+        with self.open(support.TESTFN, "ab", buffering=0) as f:
+            self.assertEqual(f.tell(), 3)
+        with self.open(support.TESTFN, "ab") as f:
+            self.assertEqual(f.tell(), 3)
+        with self.open(support.TESTFN, "a") as f:
+            self.assertTrue(f.tell() > 0)
+
+    def test_destructor(self):
+        record = []
+        class MyFileIO(self.FileIO):
+            def __del__(self):
+                record.append(1)
+                try:
+                    f = super(MyFileIO, self).__del__
+                except AttributeError:
+                    pass
+                else:
+                    f()
+            def close(self):
+                record.append(2)
+                super(MyFileIO, self).close()
+            def flush(self):
+                record.append(3)
+                super(MyFileIO, self).flush()
+        f = MyFileIO(support.TESTFN, "wb")
+        f.write(b"xxx")
+        del f
+        support.gc_collect()
+        self.assertEqual(record, [1, 2, 3])
+        with self.open(support.TESTFN, "rb") as f:
+            self.assertEqual(f.read(), b"xxx")
+
+    def _check_base_destructor(self, base):
+        record = []
+        class MyIO(base):
+            def __init__(self):
+                # This exercises the availability of attributes on object
+                # destruction.
+                # (in the C version, close() is called by the tp_dealloc
+                # function, not by __del__)
+                self.on_del = 1
+                self.on_close = 2
+                self.on_flush = 3
+            def __del__(self):
+                record.append(self.on_del)
+                try:
+                    f = super(MyIO, self).__del__
+                except AttributeError:
+                    pass
+                else:
+                    f()
+            def close(self):
+                record.append(self.on_close)
+                super(MyIO, self).close()
+            def flush(self):
+                record.append(self.on_flush)
+                super(MyIO, self).flush()
+        f = MyIO()
+        del f
+        support.gc_collect()
+        self.assertEqual(record, [1, 2, 3])
+
+    def test_IOBase_destructor(self):
+        self._check_base_destructor(self.IOBase)
+
+    def test_RawIOBase_destructor(self):
+        self._check_base_destructor(self.RawIOBase)
+
+    def test_BufferedIOBase_destructor(self):
+        self._check_base_destructor(self.BufferedIOBase)
+
+    def test_TextIOBase_destructor(self):
+        self._check_base_destructor(self.TextIOBase)
+
+    def test_close_flushes(self):
+        with self.open(support.TESTFN, "wb") as f:
+            f.write(b"xxx")
+        with self.open(support.TESTFN, "rb") as f:
+            self.assertEqual(f.read(), b"xxx")
+
+    def test_array_writes(self):
+        a = array.array(b'i', range(10))
+        n = len(a.tostring())
+        with self.open(support.TESTFN, "wb", 0) as f:
+            self.assertEqual(f.write(a), n)
+        with self.open(support.TESTFN, "wb") as f:
+            self.assertEqual(f.write(a), n)
+
+    def test_closefd(self):
+        self.assertRaises(ValueError, self.open, support.TESTFN, 'w',
+                          closefd=False)
+
+    def test_read_closed(self):
+        with self.open(support.TESTFN, "w") as f:
+            f.write("egg\n")
+        with self.open(support.TESTFN, "r") as f:
+            file = self.open(f.fileno(), "r", closefd=False)
+            self.assertEqual(file.read(), "egg\n")
+            file.seek(0)
+            file.close()
+            self.assertRaises(ValueError, file.read)
+
+    def test_no_closefd_with_filename(self):
+        # can't use closefd in combination with a file name
+        self.assertRaises(ValueError, self.open, support.TESTFN, "r", closefd=False)
+
+    def test_closefd_attr(self):
+        with self.open(support.TESTFN, "wb") as f:
+            f.write(b"egg\n")
+        with self.open(support.TESTFN, "r") as f:
+            self.assertEqual(f.buffer.raw.closefd, True)
+            file = self.open(f.fileno(), "r", closefd=False)
+            self.assertEqual(file.buffer.raw.closefd, False)
+
+    def test_garbage_collection(self):
+        # FileIO objects are collected, and collecting them flushes
+        # all data to disk.
+        f = self.FileIO(support.TESTFN, "wb")
+        f.write(b"abcxxx")
+        f.f = f
+        wr = weakref.ref(f)
+        del f
+        support.gc_collect()
+        self.assertTrue(wr() is None, wr)
+        with self.open(support.TESTFN, "rb") as f:
+            self.assertEqual(f.read(), b"abcxxx")
+
+    def test_unbounded_file(self):
+        # Issue #1174606: reading from an unbounded stream such as /dev/zero.
+        zero = "/dev/zero"
+        if not os.path.exists(zero):
+            self.skipTest("{0} does not exist".format(zero))
+        if sys.maxsize > 0x7FFFFFFF:
+            self.skipTest("test can only run in a 32-bit address space")
+        if support.real_max_memuse < support._2G:
+            self.skipTest("test requires at least 2GB of memory")
+        with self.open(zero, "rb", buffering=0) as f:
+            self.assertRaises(OverflowError, f.read)
+        with self.open(zero, "rb") as f:
+            self.assertRaises(OverflowError, f.read)
+        with self.open(zero, "r") as f:
+            self.assertRaises(OverflowError, f.read)
+
+    def test_flush_error_on_close(self):
+        f = self.open(support.TESTFN, "wb", buffering=0)
+        def bad_flush():
+            raise IOError()
+        f.flush = bad_flush
+        self.assertRaises(IOError, f.close) # exception not swallowed
+
+    def test_multi_close(self):
+        f = self.open(support.TESTFN, "wb", buffering=0)
+        f.close()
+        f.close()
+        f.close()
+        self.assertRaises(ValueError, f.flush)
+
+    def test_RawIOBase_read(self):
+        # Exercise the default RawIOBase.read() implementation (which calls
+        # readinto() internally).
+        rawio = self.MockRawIOWithoutRead((b"abc", b"d", None, b"efg", None))
+        self.assertEqual(rawio.read(2), b"ab")
+        self.assertEqual(rawio.read(2), b"c")
+        self.assertEqual(rawio.read(2), b"d")
+        self.assertEqual(rawio.read(2), None)
+        self.assertEqual(rawio.read(2), b"ef")
+        self.assertEqual(rawio.read(2), b"g")
+        self.assertEqual(rawio.read(2), None)
+        self.assertEqual(rawio.read(2), b"")
+
+class CIOTest(IOTest):
+
+    def test_IOBase_finalize(self):
+        # Issue #12149: segmentation fault on _PyIOBase_finalize when both a
+        # class which inherits IOBase and an object of this class are caught
+        # in a reference cycle and close() is already in the method cache.
+        class MyIO(self.IOBase):
+            def close(self):
+                pass
+
+        # create an instance to populate the method cache
+        MyIO()
+        obj = MyIO()
+        obj.obj = obj
+        wr = weakref.ref(obj)
+        del MyIO
+        del obj
+        support.gc_collect()
+        self.assertTrue(wr() is None, wr)
+
+class PyIOTest(IOTest):
+    test_array_writes = unittest.skip(
+        "len(array.array) returns number of elements rather than bytelength"
+    )(IOTest.test_array_writes)
+
+
+class CommonBufferedTests:
+    # Tests common to BufferedReader, BufferedWriter and BufferedRandom
+
+    def test_detach(self):
+        raw = self.MockRawIO()
+        buf = self.tp(raw)
+        self.assertIs(buf.detach(), raw)
+        self.assertRaises(ValueError, buf.detach)
+
+    def test_fileno(self):
+        rawio = self.MockRawIO()
+        bufio = self.tp(rawio)
+
+        self.assertEqual(42, bufio.fileno())
+
+    def test_no_fileno(self):
+        # XXX will we always have fileno() function? If so, kill
+        # this test. Else, write it.
+        pass
+
+    def test_invalid_args(self):
+        rawio = self.MockRawIO()
+        bufio = self.tp(rawio)
+        # Invalid whence
+        self.assertRaises(ValueError, bufio.seek, 0, -1)
+        self.assertRaises(ValueError, bufio.seek, 0, 3)
+
+    def test_override_destructor(self):
+        tp = self.tp
+        record = []
+        class MyBufferedIO(tp):
+            def __del__(self):
+                record.append(1)
+                try:
+                    f = super(MyBufferedIO, self).__del__
+                except AttributeError:
+                    pass
+                else:
+                    f()
+            def close(self):
+                record.append(2)
+                super(MyBufferedIO, self).close()
+            def flush(self):
+                record.append(3)
+                super(MyBufferedIO, self).flush()
+        rawio = self.MockRawIO()
+        bufio = MyBufferedIO(rawio)
+        writable = bufio.writable()
+        del bufio
+        support.gc_collect()
+        if writable:
+            self.assertEqual(record, [1, 2, 3])
+        else:
+            self.assertEqual(record, [1, 2])
+
+    def test_context_manager(self):
+        # Test usability as a context manager
+        rawio = self.MockRawIO()
+        bufio = self.tp(rawio)
+        def _with():
+            with bufio:
+                pass
+        _with()
+        # bufio should now be closed, and using it a second time should raise
+        # a ValueError.
+        self.assertRaises(ValueError, _with)
+
+    def test_error_through_destructor(self):
+        # Test that the exception state is not modified by a destructor,
+        # even if close() fails.
+        rawio = self.CloseFailureIO()
+        def f():
+            self.tp(rawio).xyzzy
+        with support.captured_output("stderr") as s:
+            self.assertRaises(AttributeError, f)
+        s = s.getvalue().strip()
+        if s:
+            # The destructor *may* have printed an unraisable error, check it
+            self.assertEqual(len(s.splitlines()), 1)
+            self.assertTrue(s.startswith("Exception IOError: "), s)
+            self.assertTrue(s.endswith(" ignored"), s)
+
+    def test_repr(self):
+        raw = self.MockRawIO()
+        b = self.tp(raw)
+        clsname = "%s.%s" % (self.tp.__module__, self.tp.__name__)
+        self.assertEqual(repr(b), "<%s>" % clsname)
+        raw.name = "dummy"
+        self.assertEqual(repr(b), "<%s name=u'dummy'>" % clsname)
+        raw.name = b"dummy"
+        self.assertEqual(repr(b), "<%s name='dummy'>" % clsname)
+
+    def test_flush_error_on_close(self):
+        raw = self.MockRawIO()
+        def bad_flush():
+            raise IOError()
+        raw.flush = bad_flush
+        b = self.tp(raw)
+        self.assertRaises(IOError, b.close) # exception not swallowed
+
+    def test_multi_close(self):
+        raw = self.MockRawIO()
+        b = self.tp(raw)
+        b.close()
+        b.close()
+        b.close()
+        self.assertRaises(ValueError, b.flush)
+
+    def test_readonly_attributes(self):
+        raw = self.MockRawIO()
+        buf = self.tp(raw)
+        x = self.MockRawIO()
+        with self.assertRaises((AttributeError, TypeError)):
+            buf.raw = x
+
+
+class BufferedReaderTest(unittest.TestCase, CommonBufferedTests):
+    read_mode = "rb"
+
+    def test_constructor(self):
+        rawio = self.MockRawIO([b"abc"])
+        bufio = self.tp(rawio)
+        bufio.__init__(rawio)
+        bufio.__init__(rawio, buffer_size=1024)
+        bufio.__init__(rawio, buffer_size=16)
+        self.assertEqual(b"abc", bufio.read())
+        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=0)
+        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-16)
+        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-1)
+        rawio = self.MockRawIO([b"abc"])
+        bufio.__init__(rawio)
+        self.assertEqual(b"abc", bufio.read())
+
+    def test_read(self):
+        for arg in (None, 7):
+            rawio = self.MockRawIO((b"abc", b"d", b"efg"))
+            bufio = self.tp(rawio)
+            self.assertEqual(b"abcdefg", bufio.read(arg))
+        # Invalid args
+        self.assertRaises(ValueError, bufio.read, -2)
+
+    def test_read1(self):
+        rawio = self.MockRawIO((b"abc", b"d", b"efg"))
+        bufio = self.tp(rawio)
+        self.assertEqual(b"a", bufio.read(1))
+        self.assertEqual(b"b", bufio.read1(1))
+        self.assertEqual(rawio._reads, 1)
+        self.assertEqual(b"c", bufio.read1(100))
+        self.assertEqual(rawio._reads, 1)
+        self.assertEqual(b"d", bufio.read1(100))
+        self.assertEqual(rawio._reads, 2)
+        self.assertEqual(b"efg", bufio.read1(100))
+        self.assertEqual(rawio._reads, 3)
+        self.assertEqual(b"", bufio.read1(100))
+        self.assertEqual(rawio._reads, 4)
+        # Invalid args
+        self.assertRaises(ValueError, bufio.read1, -1)
+
+    def test_readinto(self):
+        rawio = self.MockRawIO((b"abc", b"d", b"efg"))
+        bufio = self.tp(rawio)
+        b = bytearray(2)
+        self.assertEqual(bufio.readinto(b), 2)
+        self.assertEqual(b, b"ab")
+        self.assertEqual(bufio.readinto(b), 2)
+        self.assertEqual(b, b"cd")
+        self.assertEqual(bufio.readinto(b), 2)
+        self.assertEqual(b, b"ef")
+        self.assertEqual(bufio.readinto(b), 1)
+        self.assertEqual(b, b"gf")
+        self.assertEqual(bufio.readinto(b), 0)
+        self.assertEqual(b, b"gf")
+
+    def test_readlines(self):
+        def bufio():
+            rawio = self.MockRawIO((b"abc\n", b"d\n", b"ef"))
+            return self.tp(rawio)
+        self.assertEqual(bufio().readlines(), [b"abc\n", b"d\n", b"ef"])
+        self.assertEqual(bufio().readlines(5), [b"abc\n", b"d\n"])
+        self.assertEqual(bufio().readlines(None), [b"abc\n", b"d\n", b"ef"])
+
+    def test_buffering(self):
+        data = b"abcdefghi"
+        dlen = len(data)
+
+        tests = [
+            [ 100, [ 3, 1, 4, 8 ], [ dlen, 0 ] ],
+            [ 100, [ 3, 3, 3],     [ dlen ]    ],
+            [   4, [ 1, 2, 4, 2 ], [ 4, 4, 1 ] ],
+        ]
+
+        for bufsize, buf_read_sizes, raw_read_sizes in tests:
+            rawio = self.MockFileIO(data)
+            bufio = self.tp(rawio, buffer_size=bufsize)
+            pos = 0
+            for nbytes in buf_read_sizes:
+                self.assertEqual(bufio.read(nbytes), data[pos:pos+nbytes])
+                pos += nbytes
+            # this is mildly implementation-dependent
+            self.assertEqual(rawio.read_history, raw_read_sizes)
+
+    def test_read_non_blocking(self):
+        # Inject some None's in there to simulate EWOULDBLOCK
+        rawio = self.MockRawIO((b"abc", b"d", None, b"efg", None, None, None))
+        bufio = self.tp(rawio)
+        self.assertEqual(b"abcd", bufio.read(6))
+        self.assertEqual(b"e", bufio.read(1))
+        self.assertEqual(b"fg", bufio.read())
+        self.assertEqual(b"", bufio.peek(1))
+        self.assertIsNone(bufio.read())
+        self.assertEqual(b"", bufio.read())
+
+        rawio = self.MockRawIO((b"a", None, None))
+        self.assertEqual(b"a", rawio.readall())
+        self.assertIsNone(rawio.readall())
+
+    def test_read_past_eof(self):
+        rawio = self.MockRawIO((b"abc", b"d", b"efg"))
+        bufio = self.tp(rawio)
+
+        self.assertEqual(b"abcdefg", bufio.read(9000))
+
+    def test_read_all(self):
+        rawio = self.MockRawIO((b"abc", b"d", b"efg"))
+        bufio = self.tp(rawio)
+
+        self.assertEqual(b"abcdefg", bufio.read())
+
+    @unittest.skipUnless(threading, 'Threading required for this test.')
+    @support.requires_resource('cpu')
+    def test_threads(self):
+        try:
+            # Write out many bytes with exactly the same number of 0's,
+            # 1's... 255's. This will help us check that concurrent reading
+            # doesn't duplicate or forget contents.
+            N = 1000
+            l = list(range(256)) * N
+            random.shuffle(l)
+            s = bytes(bytearray(l))
+            with self.open(support.TESTFN, "wb") as f:
+                f.write(s)
+            with self.open(support.TESTFN, self.read_mode, buffering=0) as raw:
+                bufio = self.tp(raw, 8)
+                errors = []
+                results = []
+                def f():
+                    try:
+                        # Intra-buffer read then buffer-flushing read
+                        for n in cycle([1, 19]):
+                            s = bufio.read(n)
+                            if not s:
+                                break
+                            # list.append() is atomic
+                            results.append(s)
+                    except Exception as e:
+                        errors.append(e)
+                        raise
+                threads = [threading.Thread(target=f) for x in range(20)]
+                for t in threads:
+                    t.start()
+                time.sleep(0.02) # yield
+                for t in threads:
+                    t.join()
+                self.assertFalse(errors,
+                    "the following exceptions were caught: %r" % errors)
+                s = b''.join(results)
+                for i in range(256):
+                    c = bytes(bytearray([i]))
+                    self.assertEqual(s.count(c), N)
+        finally:
+            support.unlink(support.TESTFN)
+
+    def test_misbehaved_io(self):
+        rawio = self.MisbehavedRawIO((b"abc", b"d", b"efg"))
+        bufio = self.tp(rawio)
+        self.assertRaises(IOError, bufio.seek, 0)
+        self.assertRaises(IOError, bufio.tell)
+
+    def test_no_extraneous_read(self):
+        # Issue #9550; when the raw IO object has satisfied the read request,
+        # we should not issue any additional reads, otherwise it may block
+        # (e.g. socket).
+        bufsize = 16
+        for n in (2, bufsize - 1, bufsize, bufsize + 1, bufsize * 2):
+            rawio = self.MockRawIO([b"x" * n])
+            bufio = self.tp(rawio, bufsize)
+            self.assertEqual(bufio.read(n), b"x" * n)
+            # Simple case: one raw read is enough to satisfy the request.
+            self.assertEqual(rawio._extraneous_reads, 0,
+                             "failed for {}: {} != 0".format(n, rawio._extraneous_reads))
+            # A more complex case where two raw reads are needed to satisfy
+            # the request.
+            rawio = self.MockRawIO([b"x" * (n - 1), b"x"])
+            bufio = self.tp(rawio, bufsize)
+            self.assertEqual(bufio.read(n), b"x" * n)
+            self.assertEqual(rawio._extraneous_reads, 0,
+                             "failed for {}: {} != 0".format(n, rawio._extraneous_reads))
+
+
+class CBufferedReaderTest(BufferedReaderTest):
+    tp = io.BufferedReader
+
+    def test_constructor(self):
+        BufferedReaderTest.test_constructor(self)
+        # The allocation can succeed on 32-bit builds, e.g. with more
+        # than 2GB RAM and a 64-bit kernel.
+        if sys.maxsize > 0x7FFFFFFF:
+            rawio = self.MockRawIO()
+            bufio = self.tp(rawio)
+            self.assertRaises((OverflowError, MemoryError, ValueError),
+                bufio.__init__, rawio, sys.maxsize)
+
+    def test_initialization(self):
+        rawio = self.MockRawIO([b"abc"])
+        bufio = self.tp(rawio)
+        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=0)
+        self.assertRaises(ValueError, bufio.read)
+        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-16)
+        self.assertRaises(ValueError, bufio.read)
+        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-1)
+        self.assertRaises(ValueError, bufio.read)
+
+    def test_misbehaved_io_read(self):
+        rawio = self.MisbehavedRawIO((b"abc", b"d", b"efg"))
+        bufio = self.tp(rawio)
+        # _pyio.BufferedReader seems to implement reading different, so that
+        # checking this is not so easy.
+        self.assertRaises(IOError, bufio.read, 10)
+
+    def test_garbage_collection(self):
+        # C BufferedReader objects are collected.
+        # The Python version has __del__, so it ends into gc.garbage instead
+        rawio = self.FileIO(support.TESTFN, "w+b")
+        f = self.tp(rawio)
+        f.f = f
+        wr = weakref.ref(f)
+        del f
+        support.gc_collect()
+        self.assertTrue(wr() is None, wr)
+
+class PyBufferedReaderTest(BufferedReaderTest):
+    tp = pyio.BufferedReader
+
+
+class BufferedWriterTest(unittest.TestCase, CommonBufferedTests):
+    write_mode = "wb"
+
+    def test_constructor(self):
+        rawio = self.MockRawIO()
+        bufio = self.tp(rawio)
+        bufio.__init__(rawio)
+        bufio.__init__(rawio, buffer_size=1024)
+        bufio.__init__(rawio, buffer_size=16)
+        self.assertEqual(3, bufio.write(b"abc"))
+        bufio.flush()
+        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=0)
+        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-16)
+        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-1)
+        bufio.__init__(rawio)
+        self.assertEqual(3, bufio.write(b"ghi"))
+        bufio.flush()
+        self.assertEqual(b"".join(rawio._write_stack), b"abcghi")
+
+    def test_detach_flush(self):
+        raw = self.MockRawIO()
+        buf = self.tp(raw)
+        buf.write(b"howdy!")
+        self.assertFalse(raw._write_stack)
+        buf.detach()
+        self.assertEqual(raw._write_stack, [b"howdy!"])
+
+    def test_write(self):
+        # Write to the buffered IO but don't overflow the buffer.
+        writer = self.MockRawIO()
+        bufio = self.tp(writer, 8)
+        bufio.write(b"abc")
+        self.assertFalse(writer._write_stack)
+
+    def test_write_overflow(self):
+        writer = self.MockRawIO()
+        bufio = self.tp(writer, 8)
+        contents = b"abcdefghijklmnop"
+        for n in range(0, len(contents), 3):
+            bufio.write(contents[n:n+3])
+        flushed = b"".join(writer._write_stack)
+        # At least (total - 8) bytes were implicitly flushed, perhaps more
+        # depending on the implementation.
+        self.assertTrue(flushed.startswith(contents[:-8]), flushed)
+
+    def check_writes(self, intermediate_func):
+        # Lots of writes, test the flushed output is as expected.
+        contents = bytes(range(256)) * 1000
+        n = 0
+        writer = self.MockRawIO()
+        bufio = self.tp(writer, 13)
+        # Generator of write sizes: repeat each N 15 times then proceed to N+1
+        def gen_sizes():
+            for size in count(1):
+                for i in range(15):
+                    yield size
+        sizes = gen_sizes()
+        while n < len(contents):
+            size = min(next(sizes), len(contents) - n)
+            self.assertEqual(bufio.write(contents[n:n+size]), size)
+            intermediate_func(bufio)
+            n += size
+        bufio.flush()
+        self.assertEqual(contents,
+            b"".join(writer._write_stack))
+
+    def test_writes(self):
+        self.check_writes(lambda bufio: None)
+
+    def test_writes_and_flushes(self):
+        self.check_writes(lambda bufio: bufio.flush())
+
+    def test_writes_and_seeks(self):
+        def _seekabs(bufio):
+            pos = bufio.tell()
+            bufio.seek(pos + 1, 0)
+            bufio.seek(pos - 1, 0)
+            bufio.seek(pos, 0)
+        self.check_writes(_seekabs)
+        def _seekrel(bufio):
+            pos = bufio.seek(0, 1)
+            bufio.seek(+1, 1)
+            bufio.seek(-1, 1)
+            bufio.seek(pos, 0)
+        self.check_writes(_seekrel)
+
+    def test_writes_and_truncates(self):
+        self.check_writes(lambda bufio: bufio.truncate(bufio.tell()))
+
+    def test_write_non_blocking(self):
+        raw = self.MockNonBlockWriterIO()
+        bufio = self.tp(raw, 8)
+
+        self.assertEqual(bufio.write(b"abcd"), 4)
+        self.assertEqual(bufio.write(b"efghi"), 5)
+        # 1 byte will be written, the rest will be buffered
+        raw.block_on(b"k")
+        self.assertEqual(bufio.write(b"jklmn"), 5)
+
+        # 8 bytes will be written, 8 will be buffered and the rest will be lost
+        raw.block_on(b"0")
+        try:
+            bufio.write(b"opqrwxyz0123456789")
+        except self.BlockingIOError as e:
+            written = e.characters_written
+        else:
+            self.fail("BlockingIOError should have been raised")
+        self.assertEqual(written, 16)
+        self.assertEqual(raw.pop_written(),
+            b"abcdefghijklmnopqrwxyz")
+
+        self.assertEqual(bufio.write(b"ABCDEFGHI"), 9)
+        s = raw.pop_written()
+        # Previously buffered bytes were flushed
+        self.assertTrue(s.startswith(b"01234567A"), s)
+
+    def test_write_and_rewind(self):
+        raw = io.BytesIO()
+        bufio = self.tp(raw, 4)
+        self.assertEqual(bufio.write(b"abcdef"), 6)
+        self.assertEqual(bufio.tell(), 6)
+        bufio.seek(0, 0)
+        self.assertEqual(bufio.write(b"XY"), 2)
+        bufio.seek(6, 0)
+        self.assertEqual(raw.getvalue(), b"XYcdef")
+        self.assertEqual(bufio.write(b"123456"), 6)
+        bufio.flush()
+        self.assertEqual(raw.getvalue(), b"XYcdef123456")
+
+    def test_flush(self):
+        writer = self.MockRawIO()
+        bufio = self.tp(writer, 8)
+        bufio.write(b"abc")
+        bufio.flush()
+        self.assertEqual(b"abc", writer._write_stack[0])
+
+    def test_destructor(self):
+        writer = self.MockRawIO()
+        bufio = self.tp(writer, 8)
+        bufio.write(b"abc")
+        del bufio
+        support.gc_collect()
+        self.assertEqual(b"abc", writer._write_stack[0])
+
+    def test_truncate(self):
+        # Truncate implicitly flushes the buffer.
+        with self.open(support.TESTFN, self.write_mode, buffering=0) as raw:
+            bufio = self.tp(raw, 8)
+            bufio.write(b"abcdef")
+            self.assertEqual(bufio.truncate(3), 3)
+            self.assertEqual(bufio.tell(), 6)
+        with self.open(support.TESTFN, "rb", buffering=0) as f:
+            self.assertEqual(f.read(), b"abc")
+
+    @unittest.skipUnless(threading, 'Threading required for this test.')
+    @support.requires_resource('cpu')
+    def test_threads(self):
+        try:
+            # Write out many bytes from many threads and test they were
+            # all flushed.
+            N = 1000
+            contents = bytes(range(256)) * N
+            sizes = cycle([1, 19])
+            n = 0
+            queue = deque()
+            while n < len(contents):
+                size = next(sizes)
+                queue.append(contents[n:n+size])
+                n += size
+            del contents
+            # We use a real file object because it allows us to
+            # exercise situations where the GIL is released before
+            # writing the buffer to the raw streams. This is in addition
+            # to concurrency issues due to switching threads in the middle
+            # of Python code.
+            with self.open(support.TESTFN, self.write_mode, buffering=0) as raw:
+                bufio = self.tp(raw, 8)
+                errors = []
+                def f():
+                    try:
+                        while True:
+                            try:
+                                s = queue.popleft()
+                            except IndexError:
+                                return
+                            bufio.write(s)
+                    except Exception as e:
+                        errors.append(e)
+                        raise
+                threads = [threading.Thread(target=f) for x in range(20)]
+                for t in threads:
+                    t.start()
+                time.sleep(0.02) # yield
+                for t in threads:
+                    t.join()
+                self.assertFalse(errors,
+                    "the following exceptions were caught: %r" % errors)
+                bufio.close()
+            with self.open(support.TESTFN, "rb") as f:
+                s = f.read()
+            for i in range(256):
+                self.assertEqual(s.count(bytes([i])), N)
+        finally:
+            support.unlink(support.TESTFN)
+
+    def test_misbehaved_io(self):
+        rawio = self.MisbehavedRawIO()
+        bufio = self.tp(rawio, 5)
+        self.assertRaises(IOError, bufio.seek, 0)
+        self.assertRaises(IOError, bufio.tell)
+        self.assertRaises(IOError, bufio.write, b"abcdef")
+
+    def test_max_buffer_size_deprecation(self):
+        with support.check_warnings(("max_buffer_size is deprecated",
+                                     DeprecationWarning)):
+            self.tp(self.MockRawIO(), 8, 12)
+
+
+class CBufferedWriterTest(BufferedWriterTest):
+    tp = io.BufferedWriter
+
+    def test_constructor(self):
+        BufferedWriterTest.test_constructor(self)
+        # The allocation can succeed on 32-bit builds, e.g. with more
+        # than 2GB RAM and a 64-bit kernel.
+        if sys.maxsize > 0x7FFFFFFF:
+            rawio = self.MockRawIO()
+            bufio = self.tp(rawio)
+            self.assertRaises((OverflowError, MemoryError, ValueError),
+                bufio.__init__, rawio, sys.maxsize)
+
+    def test_initialization(self):
+        rawio = self.MockRawIO()
+        bufio = self.tp(rawio)
+        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=0)
+        self.assertRaises(ValueError, bufio.write, b"def")
+        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-16)
+        self.assertRaises(ValueError, bufio.write, b"def")
+        self.assertRaises(ValueError, bufio.__init__, rawio, buffer_size=-1)
+        self.assertRaises(ValueError, bufio.write, b"def")
+
+    def test_garbage_collection(self):
+        # C BufferedWriter objects are collected, and collecting them flushes
+        # all data to disk.
+        # The Python version has __del__, so it ends into gc.garbage instead
+        rawio = self.FileIO(support.TESTFN, "w+b")
+        f = self.tp(rawio)
+        f.write(b"123xxx")
+        f.x = f
+        wr = weakref.ref(f)
+        del f
+        support.gc_collect()
+        self.assertTrue(wr() is None, wr)
+        with self.open(support.TESTFN, "rb") as f:
+            self.assertEqual(f.read(), b"123xxx")
+
+
+class PyBufferedWriterTest(BufferedWriterTest):
+    tp = pyio.BufferedWriter
+
+class BufferedRWPairTest(unittest.TestCase):
+
+    def test_constructor(self):
+        pair = self.tp(self.MockRawIO(), self.MockRawIO())
+        self.assertFalse(pair.closed)
+
+    def test_detach(self):
+        pair = self.tp(self.MockRawIO(), self.MockRawIO())
+        self.assertRaises(self.UnsupportedOperation, pair.detach)
+
+    def test_constructor_max_buffer_size_deprecation(self):
+        with support.check_warnings(("max_buffer_size is deprecated",
+                                     DeprecationWarning)):
+            self.tp(self.MockRawIO(), self.MockRawIO(), 8, 12)
+
+    def test_constructor_with_not_readable(self):
+        class NotReadable(MockRawIO):
+            def readable(self):
+                return False
+
+        self.assertRaises(IOError, self.tp, NotReadable(), self.MockRawIO())
+
+    def test_constructor_with_not_writeable(self):
+        class NotWriteable(MockRawIO):
+            def writable(self):
+                return False
+
+        self.assertRaises(IOError, self.tp, self.MockRawIO(), NotWriteable())
+
+    def test_read(self):
+        pair = self.tp(self.BytesIO(b"abcdef"), self.MockRawIO())
+
+        self.assertEqual(pair.read(3), b"abc")
+        self.assertEqual(pair.read(1), b"d")
+        self.assertEqual(pair.read(), b"ef")
+        pair = self.tp(self.BytesIO(b"abc"), self.MockRawIO())
+        self.assertEqual(pair.read(None), b"abc")
+
+    def test_readlines(self):
+        pair = lambda: self.tp(self.BytesIO(b"abc\ndef\nh"), self.MockRawIO())
+        self.assertEqual(pair().readlines(), [b"abc\n", b"def\n", b"h"])
+        self.assertEqual(pair().readlines(), [b"abc\n", b"def\n", b"h"])
+        self.assertEqual(pair().readlines(5), [b"abc\n", b"def\n"])
+
+    def test_read1(self):
+        # .read1() is delegated to the underlying reader object, so this test
+        # can be shallow.
+        pair = self.tp(self.BytesIO(b"abcdef"), self.MockRawIO())
+
+        self.assertEqual(pair.read1(3), b"abc")
+
+    def test_readinto(self):
+        pair = self.tp(self.BytesIO(b"abcdef"), self.MockRawIO())
+
+        data = bytearray(5)
+        self.assertEqual(pair.readinto(data), 5)
+        self.assertEqual(data, b"abcde")
+
+    def test_write(self):
+        w = self.MockRawIO()
+        pair = self.tp(self.MockRawIO(), w)
+
+        pair.write(b"abc")
+        pair.flush()
+        pair.write(b"def")
+        pair.flush()
+        self.assertEqual(w._write_stack, [b"abc", b"def"])
+
+    def test_peek(self):
+        pair = self.tp(self.BytesIO(b"abcdef"), self.MockRawIO())
+
+        self.assertTrue(pair.peek(3).startswith(b"abc"))
+        self.assertEqual(pair.read(3), b"abc")
+
+    def test_readable(self):
+        pair = self.tp(self.MockRawIO(), self.MockRawIO())
+        self.assertTrue(pair.readable())
+
+    def test_writeable(self):
+        pair = self.tp(self.MockRawIO(), self.MockRawIO())
+        self.assertTrue(pair.writable())
+
+    def test_seekable(self):
+        # BufferedRWPairs are never seekable, even if their readers and writers
+        # are.
+        pair = self.tp(self.MockRawIO(), self.MockRawIO())
+        self.assertFalse(pair.seekable())
+
+    # .flush() is delegated to the underlying writer object and has been
+    # tested in the test_write method.
+
+    def test_close_and_closed(self):
+        pair = self.tp(self.MockRawIO(), self.MockRawIO())
+        self.assertFalse(pair.closed)
+        pair.close()
+        self.assertTrue(pair.closed)
+
+    def test_isatty(self):
+        class SelectableIsAtty(MockRawIO):
+            def __init__(self, isatty):
+                MockRawIO.__init__(self)
+                self._isatty = isatty
+
+            def isatty(self):
+                return self._isatty
+
+        pair = self.tp(SelectableIsAtty(False), SelectableIsAtty(False))
+        self.assertFalse(pair.isatty())
+
+        pair = self.tp(SelectableIsAtty(True), SelectableIsAtty(False))
+        self.assertTrue(pair.isatty())
+
+        pair = self.tp(SelectableIsAtty(False), SelectableIsAtty(True))
+        self.assertTrue(pair.isatty())
+
+        pair = self.tp(SelectableIsAtty(True), SelectableIsAtty(True))
+        self.assertTrue(pair.isatty())
+
+class CBufferedRWPairTest(BufferedRWPairTest):
+    tp = io.BufferedRWPair
+
+class PyBufferedRWPairTest(BufferedRWPairTest):
+    tp = pyio.BufferedRWPair
+
+
+class BufferedRandomTest(BufferedReaderTest, BufferedWriterTest):
+    read_mode = "rb+"
+    write_mode = "wb+"
+
+    def test_constructor(self):
+        BufferedReaderTest.test_constructor(self)
+        BufferedWriterTest.test_constructor(self)
+
+    def test_read_and_write(self):
+        raw = self.MockRawIO((b"asdf", b"ghjk"))
+        rw = self.tp(raw, 8)
+
+        self.assertEqual(b"as", rw.read(2))
+        rw.write(b"ddd")
+        rw.write(b"eee")
+        self.assertFalse(raw._write_stack) # Buffer writes
+        self.assertEqual(b"ghjk", rw.read())
+        self.assertEqual(b"dddeee", raw._write_stack[0])
+
+    def test_seek_and_tell(self):
+        raw = self.BytesIO(b"asdfghjkl")
+        rw = self.tp(raw)
+
+        self.assertEqual(b"as", rw.read(2))
+        self.assertEqual(2, rw.tell())
+        rw.seek(0, 0)
+        self.assertEqual(b"asdf", rw.read(4))
+
+        rw.write(b"123f")
+        rw.seek(0, 0)
+        self.assertEqual(b"asdf123fl", rw.read())
+        self.assertEqual(9, rw.tell())
+        rw.seek(-4, 2)
+        self.assertEqual(5, rw.tell())
+        rw.seek(2, 1)
+        self.assertEqual(7, rw.tell())
+        self.assertEqual(b"fl", rw.read(11))
+        rw.flush()
+        self.assertEqual(b"asdf123fl", raw.getvalue())
+
+        self.assertRaises(TypeError, rw.seek, 0.0)
+
+    def check_flush_and_read(self, read_func):
+        raw = self.BytesIO(b"abcdefghi")
+        bufio = self.tp(raw)
+
+        self.assertEqual(b"ab", read_func(bufio, 2))
+        bufio.write(b"12")
+        self.assertEqual(b"ef", read_func(bufio, 2))
+        self.assertEqual(6, bufio.tell())
+        bufio.flush()
+        self.assertEqual(6, bufio.tell())
+        self.assertEqual(b"ghi", read_func(bufio))
+        raw.seek(0, 0)
+        raw.write(b"XYZ")
+        # flush() resets the read buffer
+        bufio.flush()
+        bufio.seek(0, 0)
+        self.assertEqual(b"XYZ", read_func(bufio, 3))
+
+    def test_flush_and_read(self):
+        self.check_flush_and_read(lambda bufio, *args: bufio.read(*args))
+
+    def test_flush_and_readinto(self):
+        def _readinto(bufio, n=-1):
+            b = bytearray(n if n >= 0 else 9999)
+            n = bufio.readinto(b)
+            return bytes(b[:n])
+        self.check_flush_and_read(_readinto)
+
+    def test_flush_and_peek(self):
+        def _peek(bufio, n=-1):
+            # This relies on the fact that the buffer can contain the whole
+            # raw stream, otherwise peek() can return less.
+            b = bufio.peek(n)
+            if n != -1:
+                b = b[:n]
+            bufio.seek(len(b), 1)
+            return b
+        self.check_flush_and_read(_peek)
+
+    def test_flush_and_write(self):
+        raw = self.BytesIO(b"abcdefghi")
+        bufio = self.tp(raw)
+
+        bufio.write(b"123")
+        bufio.flush()
+        bufio.write(b"45")
+        bufio.flush()
+        bufio.seek(0, 0)
+        self.assertEqual(b"12345fghi", raw.getvalue())
+        self.assertEqual(b"12345fghi", bufio.read())
+
+    def test_threads(self):
+        BufferedReaderTest.test_threads(self)
+        BufferedWriterTest.test_threads(self)
+
+    def test_writes_and_peek(self):
+        def _peek(bufio):
+            bufio.peek(1)
+        self.check_writes(_peek)
+        def _peek(bufio):
+            pos = bufio.tell()
+            bufio.seek(-1, 1)
+            bufio.peek(1)
+            bufio.seek(pos, 0)
+        self.check_writes(_peek)
+
+    def test_writes_and_reads(self):
+        def _read(bufio):
+            bufio.seek(-1, 1)
+            bufio.read(1)
+        self.check_writes(_read)
+
+    def test_writes_and_read1s(self):
+        def _read1(bufio):
+            bufio.seek(-1, 1)
+            bufio.read1(1)
+        self.check_writes(_read1)
+
+    def test_writes_and_readintos(self):
+        def _read(bufio):
+            bufio.seek(-1, 1)
+            bufio.readinto(bytearray(1))
+        self.check_writes(_read)
+
+    def test_write_after_readahead(self):
+        # Issue #6629: writing after the buffer was filled by readahead should
+        # first rewind the raw stream.
+        for overwrite_size in [1, 5]:
+            raw = self.BytesIO(b"A" * 10)
+            bufio = self.tp(raw, 4)
+            # Trigger readahead
+            self.assertEqual(bufio.read(1), b"A")
+            self.assertEqual(bufio.tell(), 1)
+            # Overwriting should rewind the raw stream if it needs so
+            bufio.write(b"B" * overwrite_size)
+            self.assertEqual(bufio.tell(), overwrite_size + 1)
+            # If the write size was smaller than the buffer size, flush() and
+            # check that rewind happens.
+            bufio.flush()
+            self.assertEqual(bufio.tell(), overwrite_size + 1)
+            s = raw.getvalue()
+            self.assertEqual(s,
+                b"A" + b"B" * overwrite_size + b"A" * (9 - overwrite_size))
+
+    def test_write_rewind_write(self):
+        # Various combinations of reading / writing / seeking backwards / writing again
+        def mutate(bufio, pos1, pos2):
+            assert pos2 >= pos1
+            # Fill the buffer
+            bufio.seek(pos1)
+            bufio.read(pos2 - pos1)
+            bufio.write(b'\x02')
+            # This writes earlier than the previous write, but still inside
+            # the buffer.
+            bufio.seek(pos1)
+            bufio.write(b'\x01')
+
+        b = b"\x80\x81\x82\x83\x84"
+        for i in range(0, len(b)):
+            for j in range(i, len(b)):
+                raw = self.BytesIO(b)
+                bufio = self.tp(raw, 100)
+                mutate(bufio, i, j)
+                bufio.flush()
+                expected = bytearray(b)
+                expected[j] = 2
+                expected[i] = 1
+                self.assertEqual(raw.getvalue(), expected,
+                                 "failed result for i=%d, j=%d" % (i, j))
+
+    def test_truncate_after_read_or_write(self):
+        raw = self.BytesIO(b"A" * 10)
+        bufio = self.tp(raw, 100)
+        self.assertEqual(bufio.read(2), b"AA") # the read buffer gets filled
+        self.assertEqual(bufio.truncate(), 2)
+        self.assertEqual(bufio.write(b"BB"), 2) # the write buffer increases
+        self.assertEqual(bufio.truncate(), 4)
+
+    def test_misbehaved_io(self):
+        BufferedReaderTest.test_misbehaved_io(self)
+        BufferedWriterTest.test_misbehaved_io(self)
+
+    def test_interleaved_read_write(self):
+        # Test for issue #12213
+        with self.BytesIO(b'abcdefgh') as raw:
+            with self.tp(raw, 100) as f:
+                f.write(b"1")
+                self.assertEqual(f.read(1), b'b')
+                f.write(b'2')
+                self.assertEqual(f.read1(1), b'd')
+                f.write(b'3')
+                buf = bytearray(1)
+                f.readinto(buf)
+                self.assertEqual(buf, b'f')
+                f.write(b'4')
+                self.assertEqual(f.peek(1), b'h')
+                f.flush()
+                self.assertEqual(raw.getvalue(), b'1b2d3f4h')
+
+        with self.BytesIO(b'abc') as raw:
+            with self.tp(raw, 100) as f:
+                self.assertEqual(f.read(1), b'a')
+                f.write(b"2")
+                self.assertEqual(f.read(1), b'c')
+                f.flush()
+                self.assertEqual(raw.getvalue(), b'a2c')
+
+    def test_interleaved_readline_write(self):
+        with self.BytesIO(b'ab\ncdef\ng\n') as raw:
+            with self.tp(raw) as f:
+                f.write(b'1')
+                self.assertEqual(f.readline(), b'b\n')
+                f.write(b'2')
+                self.assertEqual(f.readline(), b'def\n')
+                f.write(b'3')
+                self.assertEqual(f.readline(), b'\n')
+                f.flush()
+                self.assertEqual(raw.getvalue(), b'1b\n2def\n3\n')
+
+
+class CBufferedRandomTest(CBufferedReaderTest, CBufferedWriterTest, BufferedRandomTest):
+    tp = io.BufferedRandom
+
+    def test_constructor(self):
+        BufferedRandomTest.test_constructor(self)
+        # The allocation can succeed on 32-bit builds, e.g. with more
+        # than 2GB RAM and a 64-bit kernel.
+        if sys.maxsize > 0x7FFFFFFF:
+            rawio = self.MockRawIO()
+            bufio = self.tp(rawio)
+            self.assertRaises((OverflowError, MemoryError, ValueError),
+                bufio.__init__, rawio, sys.maxsize)
+
+    def test_garbage_collection(self):
+        CBufferedReaderTest.test_garbage_collection(self)
+        CBufferedWriterTest.test_garbage_collection(self)
+
+class PyBufferedRandomTest(BufferedRandomTest):
+    tp = pyio.BufferedRandom
+
+
+# To fully exercise seek/tell, the StatefulIncrementalDecoder has these
+# properties:
+#   - A single output character can correspond to many bytes of input.
+#   - The number of input bytes to complete the character can be
+#     undetermined until the last input byte is received.
+#   - The number of input bytes can vary depending on previous input.
+#   - A single input byte can correspond to many characters of output.
+#   - The number of output characters can be undetermined until the
+#     last input byte is received.
+#   - The number of output characters can vary depending on previous input.
+
+class StatefulIncrementalDecoder(codecs.IncrementalDecoder):
+    """
+    For testing seek/tell behavior with a stateful, buffering decoder.
+
+    Input is a sequence of words.  Words may be fixed-length (length set
+    by input) or variable-length (period-terminated).  In variable-length
+    mode, extra periods are ignored.  Possible words are:
+      - 'i' followed by a number sets the input length, I (maximum 99).
+        When I is set to 0, words are space-terminated.
+      - 'o' followed by a number sets the output length, O (maximum 99).
+      - Any other word is converted into a word followed by a period on
+        the output.  The output word consists of the input word truncated
+        or padded out with hyphens to make its length equal to O.  If O
+        is 0, the word is output verbatim without truncating or padding.
+    I and O are initially set to 1.  When I changes, any buffered input is
+    re-scanned according to the new I.  EOF also terminates the last word.
+    """
+
+    def __init__(self, errors='strict'):
+        codecs.IncrementalDecoder.__init__(self, errors)
+        self.reset()
+
+    def __repr__(self):
+        return '<SID %x>' % id(self)
+
+    def reset(self):
+        self.i = 1
+        self.o = 1
+        self.buffer = bytearray()
+
+    def getstate(self):
+        i, o = self.i ^ 1, self.o ^ 1 # so that flags = 0 after reset()
+        return bytes(self.buffer), i*100 + o
+
+    def setstate(self, state):
+        buffer, io = state
+        self.buffer = bytearray(buffer)
+        i, o = divmod(io, 100)
+        self.i, self.o = i ^ 1, o ^ 1
+
+    def decode(self, input, final=False):
+        output = ''
+        for b in input:
+            if self.i == 0: # variable-length, terminated with period
+                if b == '.':
+                    if self.buffer:
+                        output += self.process_word()
+                else:
+                    self.buffer.append(b)
+            else: # fixed-length, terminate after self.i bytes
+                self.buffer.append(b)
+                if len(self.buffer) == self.i:
+                    output += self.process_word()
+        if final and self.buffer: # EOF terminates the last word
+            output += self.process_word()
+        return output
+
+    def process_word(self):
+        output = ''
+        if self.buffer[0] == ord('i'):
+            self.i = min(99, int(self.buffer[1:] or 0)) # set input length
+        elif self.buffer[0] == ord('o'):
+            self.o = min(99, int(self.buffer[1:] or 0)) # set output length
+        else:
+            output = self.buffer.decode('ascii')
+            if len(output) < self.o:
+                output += '-'*self.o # pad out with hyphens
+            if self.o:
+                output = output[:self.o] # truncate to output length
+            output += '.'
+        self.buffer = bytearray()
+        return output
+
+    codecEnabled = False
+
+    @classmethod
+    def lookupTestDecoder(cls, name):
+        if cls.codecEnabled and name == 'test_decoder':
+            latin1 = codecs.lookup('latin-1')
+            return codecs.CodecInfo(
+                name='test_decoder', encode=latin1.encode, decode=None,
+                incrementalencoder=None,
+                streamreader=None, streamwriter=None,
+                incrementaldecoder=cls)
+
+# Register the previous decoder for testing.
+# Disabled by default, tests will enable it.
+codecs.register(StatefulIncrementalDecoder.lookupTestDecoder)
+
+
+class StatefulIncrementalDecoderTest(unittest.TestCase):
+    """
+    Make sure the StatefulIncrementalDecoder actually works.
+    """
+
+    test_cases = [
+        # I=1, O=1 (fixed-length input == fixed-length output)
+        (b'abcd', False, 'a.b.c.d.'),
+        # I=0, O=0 (variable-length input, variable-length output)
+        (b'oiabcd', True, 'abcd.'),
+        # I=0, O=0 (should ignore extra periods)
+        (b'oi...abcd...', True, 'abcd.'),
+        # I=0, O=6 (variable-length input, fixed-length output)
+        (b'i.o6.x.xyz.toolongtofit.', False, 'x-----.xyz---.toolon.'),
+        # I=2, O=6 (fixed-length input < fixed-length output)
+        (b'i.i2.o6xyz', True, 'xy----.z-----.'),
+        # I=6, O=3 (fixed-length input > fixed-length output)
+        (b'i.o3.i6.abcdefghijklmnop', True, 'abc.ghi.mno.'),
+        # I=0, then 3; O=29, then 15 (with longer output)
+        (b'i.o29.a.b.cde.o15.abcdefghijabcdefghij.i3.a.b.c.d.ei00k.l.m', True,
+         'a----------------------------.' +
+         'b----------------------------.' +
+         'cde--------------------------.' +
+         'abcdefghijabcde.' +
+         'a.b------------.' +
+         '.c.------------.' +
+         'd.e------------.' +
+         'k--------------.' +
+         'l--------------.' +
+         'm--------------.')
+    ]
+
+    def test_decoder(self):
+        # Try a few one-shot test cases.
+        for input, eof, output in self.test_cases:
+            d = StatefulIncrementalDecoder()
+            self.assertEqual(d.decode(input, eof), output)
+
+        # Also test an unfinished decode, followed by forcing EOF.
+        d = StatefulIncrementalDecoder()
+        self.assertEqual(d.decode(b'oiabcd'), '')
+        self.assertEqual(d.decode(b'', 1), 'abcd.')
+
+class TextIOWrapperTest(unittest.TestCase):
+
+    def setUp(self):
+        self.testdata = b"AAA\r\nBBB\rCCC\r\nDDD\nEEE\r\n"
+        self.normalized = b"AAA\nBBB\nCCC\nDDD\nEEE\n".decode("ascii")
+        support.unlink(support.TESTFN)
+
+    def tearDown(self):
+        support.unlink(support.TESTFN)
+
+    def test_constructor(self):
+        r = self.BytesIO(b"\xc3\xa9\n\n")
+        b = self.BufferedReader(r, 1000)
+        t = self.TextIOWrapper(b)
+        t.__init__(b, encoding="latin1", newline="\r\n")
+        self.assertEqual(t.encoding, "latin1")
+        self.assertEqual(t.line_buffering, False)
+        t.__init__(b, encoding="utf8", line_buffering=True)
+        self.assertEqual(t.encoding, "utf8")
+        self.assertEqual(t.line_buffering, True)
+        self.assertEqual("\xe9\n", t.readline())
+        self.assertRaises(TypeError, t.__init__, b, newline=42)
+        self.assertRaises(ValueError, t.__init__, b, newline='xyzzy')
+
+    def test_detach(self):
+        r = self.BytesIO()
+        b = self.BufferedWriter(r)
+        t = self.TextIOWrapper(b)
+        self.assertIs(t.detach(), b)
+
+        t = self.TextIOWrapper(b, encoding="ascii")
+        t.write("howdy")
+        self.assertFalse(r.getvalue())
+        t.detach()
+        self.assertEqual(r.getvalue(), b"howdy")
+        self.assertRaises(ValueError, t.detach)
+
+    def test_repr(self):
+        raw = self.BytesIO("hello".encode("utf-8"))
+        b = self.BufferedReader(raw)
+        t = self.TextIOWrapper(b, encoding="utf-8")
+        modname = self.TextIOWrapper.__module__
+        self.assertEqual(repr(t),
+                         "<%s.TextIOWrapper encoding='utf-8'>" % modname)
+        raw.name = "dummy"
+        self.assertEqual(repr(t),
+                         "<%s.TextIOWrapper name=u'dummy' encoding='utf-8'>" % modname)
+        raw.name = b"dummy"
+        self.assertEqual(repr(t),
+                         "<%s.TextIOWrapper name='dummy' encoding='utf-8'>" % modname)
+
+    def test_line_buffering(self):
+        r = self.BytesIO()
+        b = self.BufferedWriter(r, 1000)
+        t = self.TextIOWrapper(b, newline="\n", line_buffering=True)
+        t.write("X")
+        self.assertEqual(r.getvalue(), b"")  # No flush happened
+        t.write("Y\nZ")
+        self.assertEqual(r.getvalue(), b"XY\nZ")  # All got flushed
+        t.write("A\rB")
+        self.assertEqual(r.getvalue(), b"XY\nZA\rB")
+
+    def test_encoding(self):
+        # Check the encoding attribute is always set, and valid
+        b = self.BytesIO()
+        t = self.TextIOWrapper(b, encoding="utf8")
+        self.assertEqual(t.encoding, "utf8")
+        t = self.TextIOWrapper(b)
+        self.assertTrue(t.encoding is not None)
+        codecs.lookup(t.encoding)
+
+    def test_encoding_errors_reading(self):
+        # (1) default
+        b = self.BytesIO(b"abc\n\xff\n")
+        t = self.TextIOWrapper(b, encoding="ascii")
+        self.assertRaises(UnicodeError, t.read)
+        # (2) explicit strict
+        b = self.BytesIO(b"abc\n\xff\n")
+        t = self.TextIOWrapper(b, encoding="ascii", errors="strict")
+        self.assertRaises(UnicodeError, t.read)
+        # (3) ignore
+        b = self.BytesIO(b"abc\n\xff\n")
+        t = self.TextIOWrapper(b, encoding="ascii", errors="ignore")
+        self.assertEqual(t.read(), "abc\n\n")
+        # (4) replace
+        b = self.BytesIO(b"abc\n\xff\n")
+        t = self.TextIOWrapper(b, encoding="ascii", errors="replace")
+        self.assertEqual(t.read(), "abc\n\ufffd\n")
+
+    def test_encoding_errors_writing(self):
+        # (1) default
+        b = self.BytesIO()
+        t = self.TextIOWrapper(b, encoding="ascii")
+        self.assertRaises(UnicodeError, t.write, "\xff")
+        # (2) explicit strict
+        b = self.BytesIO()
+        t = self.TextIOWrapper(b, encoding="ascii", errors="strict")
+        self.assertRaises(UnicodeError, t.write, "\xff")
+        # (3) ignore
+        b = self.BytesIO()
+        t = self.TextIOWrapper(b, encoding="ascii", errors="ignore",
+                             newline="\n")
+        t.write("abc\xffdef\n")
+        t.flush()
+        self.assertEqual(b.getvalue(), b"abcdef\n")
+        # (4) replace
+        b = self.BytesIO()
+        t = self.TextIOWrapper(b, encoding="ascii", errors="replace",
+                             newline="\n")
+        t.write("abc\xffdef\n")
+        t.flush()
+        self.assertEqual(b.getvalue(), b"abc?def\n")
+
+    def test_newlines(self):
+        input_lines = [ "unix\n", "windows\r\n", "os9\r", "last\n", "nonl" ]
+
+        tests = [
+            [ None, [ 'unix\n', 'windows\n', 'os9\n', 'last\n', 'nonl' ] ],
+            [ '', input_lines ],
+            [ '\n', [ "unix\n", "windows\r\n", "os9\rlast\n", "nonl" ] ],
+            [ '\r\n', [ "unix\nwindows\r\n", "os9\rlast\nnonl" ] ],
+            [ '\r', [ "unix\nwindows\r", "\nos9\r", "last\nnonl" ] ],
+        ]
+        encodings = (
+            'utf-8', 'latin-1',
+            'utf-16', 'utf-16-le', 'utf-16-be',
+            'utf-32', 'utf-32-le', 'utf-32-be',
+        )
+
+        # Try a range of buffer sizes to test the case where \r is the last
+        # character in TextIOWrapper._pending_line.
+        for encoding in encodings:
+            # XXX: str.encode() should return bytes
+            data = bytes(''.join(input_lines).encode(encoding))
+            for do_reads in (False, True):
+                for bufsize in range(1, 10):
+                    for newline, exp_lines in tests:
+                        bufio = self.BufferedReader(self.BytesIO(data), bufsize)
+                        textio = self.TextIOWrapper(bufio, newline=newline,
+                                                  encoding=encoding)
+                        if do_reads:
+                            got_lines = []
+                            while True:
+                                c2 = textio.read(2)
+                                if c2 == '':
+                                    break
+                                self.assertEqual(len(c2), 2)
+                                got_lines.append(c2 + textio.readline())
+                        else:
+                            got_lines = list(textio)
+
+                        for got_line, exp_line in zip(got_lines, exp_lines):
+                            self.assertEqual(got_line, exp_line)
+                        self.assertEqual(len(got_lines), len(exp_lines))
+
+    def test_newlines_input(self):
+        testdata = b"AAA\nBB\x00B\nCCC\rDDD\rEEE\r\nFFF\r\nGGG"
+        normalized = testdata.replace(b"\r\n", b"\n").replace(b"\r", b"\n")
+        for newline, expected in [
+            (None, normalized.decode("ascii").splitlines(True)),
+            ("", testdata.decode("ascii").splitlines(True)),
+            ("\n", ["AAA\n", "BB\x00B\n", "CCC\rDDD\rEEE\r\n", "FFF\r\n", "GGG"]),
+            ("\r\n", ["AAA\nBB\x00B\nCCC\rDDD\rEEE\r\n", "FFF\r\n", "GGG"]),
+            ("\r",  ["AAA\nBB\x00B\nCCC\r", "DDD\r", "EEE\r", "\nFFF\r", "\nGGG"]),
+            ]:
+            buf = self.BytesIO(testdata)
+            txt = self.TextIOWrapper(buf, encoding="ascii", newline=newline)
+            self.assertEqual(txt.readlines(), expected)
+            txt.seek(0)
+            self.assertEqual(txt.read(), "".join(expected))
+
+    def test_newlines_output(self):
+        testdict = {
+            "": b"AAA\nBBB\nCCC\nX\rY\r\nZ",
+            "\n": b"AAA\nBBB\nCCC\nX\rY\r\nZ",
+            "\r": b"AAA\rBBB\rCCC\rX\rY\r\rZ",
+            "\r\n": b"AAA\r\nBBB\r\nCCC\r\nX\rY\r\r\nZ",
+            }
+        tests = [(None, testdict[os.linesep])] + sorted(testdict.items())
+        for newline, expected in tests:
+            buf = self.BytesIO()
+            txt = self.TextIOWrapper(buf, encoding="ascii", newline=newline)
+            txt.write("AAA\nB")
+            txt.write("BB\nCCC\n")
+            txt.write("X\rY\r\nZ")
+            txt.flush()
+            self.assertEqual(buf.closed, False)
+            self.assertEqual(buf.getvalue(), expected)
+
+    def test_destructor(self):
+        l = []
+        base = self.BytesIO
+        class MyBytesIO(base):
+            def close(self):
+                l.append(self.getvalue())
+                base.close(self)
+        b = MyBytesIO()
+        t = self.TextIOWrapper(b, encoding="ascii")
+        t.write("abc")
+        del t
+        support.gc_collect()
+        self.assertEqual([b"abc"], l)
+
+    def test_override_destructor(self):
+        record = []
+        class MyTextIO(self.TextIOWrapper):
+            def __del__(self):
+                record.append(1)
+                try:
+                    f = super(MyTextIO, self).__del__
+                except AttributeError:
+                    pass
+                else:
+                    f()
+            def close(self):
+                record.append(2)
+                super(MyTextIO, self).close()
+            def flush(self):
+                record.append(3)
+                super(MyTextIO, self).flush()
+        b = self.BytesIO()
+        t = MyTextIO(b, encoding="ascii")
+        del t
+        support.gc_collect()
+        self.assertEqual(record, [1, 2, 3])
+
+    def test_error_through_destructor(self):
+        # Test that the exception state is not modified by a destructor,
+        # even if close() fails.
+        rawio = self.CloseFailureIO()
+        def f():
+            self.TextIOWrapper(rawio).xyzzy
+        with support.captured_output("stderr") as s:
+            self.assertRaises(AttributeError, f)
+        s = s.getvalue().strip()
+        if s:
+            # The destructor *may* have printed an unraisable error, check it
+            self.assertEqual(len(s.splitlines()), 1)
+            self.assertTrue(s.startswith("Exception IOError: "), s)
+            self.assertTrue(s.endswith(" ignored"), s)
+
+    # Systematic tests of the text I/O API
+
+    def test_basic_io(self):
+        for chunksize in (1, 2, 3, 4, 5, 15, 16, 17, 31, 32, 33, 63, 64, 65):
+            for enc in "ascii", "latin1", "utf8" :# , "utf-16-be", "utf-16-le":
+                f = self.open(support.TESTFN, "w+", encoding=enc)
+                f._CHUNK_SIZE = chunksize
+                self.assertEqual(f.write("abc"), 3)
+                f.close()
+                f = self.open(support.TESTFN, "r+", encoding=enc)
+                f._CHUNK_SIZE = chunksize
+                self.assertEqual(f.tell(), 0)
+                self.assertEqual(f.read(), "abc")
+                cookie = f.tell()
+                self.assertEqual(f.seek(0), 0)
+                self.assertEqual(f.read(None), "abc")
+                f.seek(0)
+                self.assertEqual(f.read(2), "ab")
+                self.assertEqual(f.read(1), "c")
+                self.assertEqual(f.read(1), "")
+                self.assertEqual(f.read(), "")
+                self.assertEqual(f.tell(), cookie)
+                self.assertEqual(f.seek(0), 0)
+                self.assertEqual(f.seek(0, 2), cookie)
+                self.assertEqual(f.write("def"), 3)
+                self.assertEqual(f.seek(cookie), cookie)
+                self.assertEqual(f.read(), "def")
+                if enc.startswith("utf"):
+                    self.multi_line_test(f, enc)
+                f.close()
+
+    def multi_line_test(self, f, enc):
+        f.seek(0)
+        f.truncate()
+        sample = "s\xff\u0fff\uffff"
+        wlines = []
+        for size in (0, 1, 2, 3, 4, 5, 30, 31, 32, 33, 62, 63, 64, 65, 1000):
+            chars = []
+            for i in range(size):
+                chars.append(sample[i % len(sample)])
+            line = "".join(chars) + "\n"
+            wlines.append((f.tell(), line))
+            f.write(line)
+        f.seek(0)
+        rlines = []
+        while True:
+            pos = f.tell()
+            line = f.readline()
+            if not line:
+                break
+            rlines.append((pos, line))
+        self.assertEqual(rlines, wlines)
+
+    def test_telling(self):
+        f = self.open(support.TESTFN, "w+", encoding="utf8")
+        p0 = f.tell()
+        f.write("\xff\n")
+        p1 = f.tell()
+        f.write("\xff\n")
+        p2 = f.tell()
+        f.seek(0)
+        self.assertEqual(f.tell(), p0)
+        self.assertEqual(f.readline(), "\xff\n")
+        self.assertEqual(f.tell(), p1)
+        self.assertEqual(f.readline(), "\xff\n")
+        self.assertEqual(f.tell(), p2)
+        f.seek(0)
+        for line in f:
+            self.assertEqual(line, "\xff\n")
+            self.assertRaises(IOError, f.tell)
+        self.assertEqual(f.tell(), p2)
+        f.close()
+
+    def test_seeking(self):
+        chunk_size = _default_chunk_size()
+        prefix_size = chunk_size - 2
+        u_prefix = "a" * prefix_size
+        prefix = bytes(u_prefix.encode("utf-8"))
+        self.assertEqual(len(u_prefix), len(prefix))
+        u_suffix = "\u8888\n"
+        suffix = bytes(u_suffix.encode("utf-8"))
+        line = prefix + suffix
+        f = self.open(support.TESTFN, "wb")
+        f.write(line*2)
+        f.close()
+        f = self.open(support.TESTFN, "r", encoding="utf-8")
+        s = f.read(prefix_size)
+        self.assertEqual(s, prefix.decode("ascii"))
+        self.assertEqual(f.tell(), prefix_size)
+        self.assertEqual(f.readline(), u_suffix)
+
+    def test_seeking_too(self):
+        # Regression test for a specific bug
+        data = b'\xe0\xbf\xbf\n'
+        f = self.open(support.TESTFN, "wb")
+        f.write(data)
+        f.close()
+        f = self.open(support.TESTFN, "r", encoding="utf-8")
+        f._CHUNK_SIZE  # Just test that it exists
+        f._CHUNK_SIZE = 2
+        f.readline()
+        f.tell()
+
+    def test_seek_and_tell(self):
+        #Test seek/tell using the StatefulIncrementalDecoder.
+        # Make test faster by doing smaller seeks
+        CHUNK_SIZE = 128
+
+        def test_seek_and_tell_with_data(data, min_pos=0):
+            """Tell/seek to various points within a data stream and ensure
+            that the decoded data returned by read() is consistent."""
+            f = self.open(support.TESTFN, 'wb')
+            f.write(data)
+            f.close()
+            f = self.open(support.TESTFN, encoding='test_decoder')
+            f._CHUNK_SIZE = CHUNK_SIZE
+            decoded = f.read()
+            f.close()
+
+            for i in range(min_pos, len(decoded) + 1): # seek positions
+                for j in [1, 5, len(decoded) - i]: # read lengths
+                    f = self.open(support.TESTFN, encoding='test_decoder')
+                    self.assertEqual(f.read(i), decoded[:i])
+                    cookie = f.tell()
+                    self.assertEqual(f.read(j), decoded[i:i + j])
+                    f.seek(cookie)
+                    self.assertEqual(f.read(), decoded[i:])
+                    f.close()
+
+        # Enable the test decoder.
+        StatefulIncrementalDecoder.codecEnabled = 1
+
+        # Run the tests.
+        try:
+            # Try each test case.
+            for input, _, _ in StatefulIncrementalDecoderTest.test_cases:
+                test_seek_and_tell_with_data(input)
+
+            # Position each test case so that it crosses a chunk boundary.
+            for input, _, _ in StatefulIncrementalDecoderTest.test_cases:
+                offset = CHUNK_SIZE - len(input)//2
+                prefix = b'.'*offset
+                # Don't bother seeking into the prefix (takes too long).
+                min_pos = offset*2
+                test_seek_and_tell_with_data(prefix + input, min_pos)
+
+        # Ensure our test decoder won't interfere with subsequent tests.
+        finally:
+            StatefulIncrementalDecoder.codecEnabled = 0
+
+    def test_encoded_writes(self):
+        data = "1234567890"
+        tests = ("utf-16",
+                 "utf-16-le",
+                 "utf-16-be",
+                 "utf-32",
+                 "utf-32-le",
+                 "utf-32-be")
+        for encoding in tests:
+            buf = self.BytesIO()
+            f = self.TextIOWrapper(buf, encoding=encoding)
+            # Check if the BOM is written only once (see issue1753).
+            f.write(data)
+            f.write(data)
+            f.seek(0)
+            self.assertEqual(f.read(), data * 2)
+            f.seek(0)
+            self.assertEqual(f.read(), data * 2)
+            self.assertEqual(buf.getvalue(), (data * 2).encode(encoding))
+
+    def test_unreadable(self):
+        class UnReadable(self.BytesIO):
+            def readable(self):
+                return False
+        txt = self.TextIOWrapper(UnReadable())
+        self.assertRaises(IOError, txt.read)
+
+    def test_read_one_by_one(self):
+        txt = self.TextIOWrapper(self.BytesIO(b"AA\r\nBB"))