From d2bf69e354467ef20e24d3dccff77664983dc48a Mon Sep 17 00:00:00 2001
From: Blues-star <469830014@qq.com>
Date: Tue, 20 Feb 2024 20:19:32 +0800
Subject: [PATCH] Update test_csv.py from CPython v3.12.0

---
 Lib/test/test_csv.py | 1441 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 1441 insertions(+)
 create mode 100644 Lib/test/test_csv.py

diff --git a/Lib/test/test_csv.py b/Lib/test/test_csv.py
new file mode 100644
index 000000000..bc9961e08
--- /dev/null
+++ b/Lib/test/test_csv.py
@@ -0,0 +1,1441 @@
+# Copyright (C) 2001,2002 Python Software Foundation
+# csv package unit tests
+
+import copy
+import sys
+import unittest
+from io import StringIO
+from tempfile import TemporaryFile
+import csv
+import gc
+import pickle
+from test import support
+from test.support import warnings_helper, import_helper, check_disallow_instantiation
+from itertools import permutations
+from textwrap import dedent
+from collections import OrderedDict
+
+
+class BadIterable:
+    def __iter__(self):
+        raise OSError
+
+
+class Test_Csv(unittest.TestCase):
+    """
+    Test the underlying C csv parser in ways that are not appropriate
+    from the high level interface. Further tests of this nature are done
+    in TestDialectRegistry.
+    """
+    def _test_arg_valid(self, ctor, arg):
+        self.assertRaises(TypeError, ctor)
+        self.assertRaises(TypeError, ctor, None)
+        self.assertRaises(TypeError, ctor, arg, bad_attr = 0)
+        self.assertRaises(TypeError, ctor, arg, delimiter = 0)
+        self.assertRaises(TypeError, ctor, arg, delimiter = 'XX')
+        self.assertRaises(csv.Error, ctor, arg, 'foo')
+        self.assertRaises(TypeError, ctor, arg, delimiter=None)
+        self.assertRaises(TypeError, ctor, arg, delimiter=1)
+        self.assertRaises(TypeError, ctor, arg, quotechar=1)
+        self.assertRaises(TypeError, ctor, arg, lineterminator=None)
+        self.assertRaises(TypeError, ctor, arg, lineterminator=1)
+        self.assertRaises(TypeError, ctor, arg, quoting=None)
+        self.assertRaises(TypeError, ctor, arg,
+                          quoting=csv.QUOTE_ALL, quotechar='')
+        self.assertRaises(TypeError, ctor, arg,
+                          quoting=csv.QUOTE_ALL, quotechar=None)
+        self.assertRaises(TypeError, ctor, arg,
+                          quoting=csv.QUOTE_NONE, quotechar='')
+
+    def test_reader_arg_valid(self):
+        self._test_arg_valid(csv.reader, [])
+        self.assertRaises(OSError, csv.reader, BadIterable())
+
+    def test_writer_arg_valid(self):
+        self._test_arg_valid(csv.writer, StringIO())
+        class BadWriter:
+            @property
+            def write(self):
+                raise OSError
+        self.assertRaises(OSError, csv.writer, BadWriter())
+
+    def _test_default_attrs(self, ctor, *args):
+        obj = ctor(*args)
+        # Check defaults
+        self.assertEqual(obj.dialect.delimiter, ',')
+        self.assertIs(obj.dialect.doublequote, True)
+        self.assertEqual(obj.dialect.escapechar, None)
+        self.assertEqual(obj.dialect.lineterminator, "\r\n")
+        self.assertEqual(obj.dialect.quotechar, '"')
+        self.assertEqual(obj.dialect.quoting, csv.QUOTE_MINIMAL)
+        self.assertIs(obj.dialect.skipinitialspace, False)
+        self.assertIs(obj.dialect.strict, False)
+        # Try deleting or changing attributes (they are read-only)
+        self.assertRaises(AttributeError, delattr, obj.dialect, 'delimiter')
+        self.assertRaises(AttributeError, setattr, obj.dialect, 'delimiter', ':')
+        self.assertRaises(AttributeError, delattr, obj.dialect, 'quoting')
+        self.assertRaises(AttributeError, setattr, obj.dialect,
+                          'quoting', None)
+
+    def test_reader_attrs(self):
+        self._test_default_attrs(csv.reader, [])
+
+    def test_writer_attrs(self):
+        self._test_default_attrs(csv.writer, StringIO())
+
+    def _test_kw_attrs(self, ctor, *args):
+        # Now try with alternate options
+        kwargs = dict(delimiter=':', doublequote=False, escapechar='\\',
+                      lineterminator='\r', quotechar='*',
+                      quoting=csv.QUOTE_NONE, skipinitialspace=True,
+                      strict=True)
+        obj = ctor(*args, **kwargs)
+        self.assertEqual(obj.dialect.delimiter, ':')
+        self.assertIs(obj.dialect.doublequote, False)
+        self.assertEqual(obj.dialect.escapechar, '\\')
+        self.assertEqual(obj.dialect.lineterminator, "\r")
+        self.assertEqual(obj.dialect.quotechar, '*')
+        self.assertEqual(obj.dialect.quoting, csv.QUOTE_NONE)
+        self.assertIs(obj.dialect.skipinitialspace, True)
+        self.assertIs(obj.dialect.strict, True)
+
+    def test_reader_kw_attrs(self):
+        self._test_kw_attrs(csv.reader, [])
+
+    def test_writer_kw_attrs(self):
+        self._test_kw_attrs(csv.writer, StringIO())
+
+    def _test_dialect_attrs(self, ctor, *args):
+        # Now try with dialect-derived options
+        class dialect:
+            delimiter='-'
+            doublequote=False
+            escapechar='^'
+            lineterminator='$'
+            quotechar='#'
+            quoting=csv.QUOTE_ALL
+            skipinitialspace=True
+            strict=False
+        args = args + (dialect,)
+        obj = ctor(*args)
+        self.assertEqual(obj.dialect.delimiter, '-')
+        self.assertIs(obj.dialect.doublequote, False)
+        self.assertEqual(obj.dialect.escapechar, '^')
+        self.assertEqual(obj.dialect.lineterminator, "$")
+        self.assertEqual(obj.dialect.quotechar, '#')
+        self.assertEqual(obj.dialect.quoting, csv.QUOTE_ALL)
+        self.assertIs(obj.dialect.skipinitialspace, True)
+        self.assertIs(obj.dialect.strict, False)
+
+    def test_reader_dialect_attrs(self):
+        self._test_dialect_attrs(csv.reader, [])
+
+    def test_writer_dialect_attrs(self):
+        self._test_dialect_attrs(csv.writer, StringIO())
+
+
+    def _write_test(self, fields, expect, **kwargs):
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj, **kwargs)
+            writer.writerow(fields)
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(),
+                             expect + writer.dialect.lineterminator)
+
+    def _write_error_test(self, exc, fields, **kwargs):
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj, **kwargs)
+            with self.assertRaises(exc):
+                writer.writerow(fields)
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), '')
+
+    def test_write_arg_valid(self):
+        self._write_error_test(csv.Error, None)
+        self._write_test((), '')
+        self._write_test([None], '""')
+        self._write_error_test(csv.Error, [None], quoting = csv.QUOTE_NONE)
+        # Check that exceptions are passed up the chain
+        self._write_error_test(OSError, BadIterable())
+        class BadList:
+            def __len__(self):
+                return 10
+            def __getitem__(self, i):
+                if i > 2:
+                    raise OSError
+        self._write_error_test(OSError, BadList())
+        class BadItem:
+            def __str__(self):
+                raise OSError
+        self._write_error_test(OSError, [BadItem()])
+
+    def test_write_bigfield(self):
+        # This exercises the buffer realloc functionality
+        bigstring = 'X' * 50000
+        self._write_test([bigstring,bigstring], '%s,%s' % \
+                         (bigstring, bigstring))
+
+    def test_write_quoting(self):
+        self._write_test(['a',1,'p,q'], 'a,1,"p,q"')
+        self._write_error_test(csv.Error, ['a',1,'p,q'],
+                               quoting = csv.QUOTE_NONE)
+        self._write_test(['a',1,'p,q'], 'a,1,"p,q"',
+                         quoting = csv.QUOTE_MINIMAL)
+        self._write_test(['a',1,'p,q'], '"a",1,"p,q"',
+                         quoting = csv.QUOTE_NONNUMERIC)
+        self._write_test(['a',1,'p,q'], '"a","1","p,q"',
+                         quoting = csv.QUOTE_ALL)
+        self._write_test(['a\nb',1], '"a\nb","1"',
+                         quoting = csv.QUOTE_ALL)
+        self._write_test(['a','',None,1], '"a","",,1',
+                         quoting = csv.QUOTE_STRINGS)
+        self._write_test(['a','',None,1], '"a","",,"1"',
+                         quoting = csv.QUOTE_NOTNULL)
+
+    def test_write_escape(self):
+        self._write_test(['a',1,'p,q'], 'a,1,"p,q"',
+                         escapechar='\\')
+        self._write_error_test(csv.Error, ['a',1,'p,"q"'],
+                               escapechar=None, doublequote=False)
+        self._write_test(['a',1,'p,"q"'], 'a,1,"p,\\"q\\""',
+                         escapechar='\\', doublequote = False)
+        self._write_test(['"'], '""""',
+                         escapechar='\\', quoting = csv.QUOTE_MINIMAL)
+        self._write_test(['"'], '\\"',
+                         escapechar='\\', quoting = csv.QUOTE_MINIMAL,
+                         doublequote = False)
+        self._write_test(['"'], '\\"',
+                         escapechar='\\', quoting = csv.QUOTE_NONE)
+        self._write_test(['a',1,'p,q'], 'a,1,p\\,q',
+                         escapechar='\\', quoting = csv.QUOTE_NONE)
+        self._write_test(['\\', 'a'], '\\\\,a',
+                         escapechar='\\', quoting=csv.QUOTE_NONE)
+        self._write_test(['\\', 'a'], '\\\\,a',
+                         escapechar='\\', quoting=csv.QUOTE_MINIMAL)
+        self._write_test(['\\', 'a'], '"\\\\","a"',
+                         escapechar='\\', quoting=csv.QUOTE_ALL)
+        self._write_test(['\\ ', 'a'], '\\\\ ,a',
+                         escapechar='\\', quoting=csv.QUOTE_MINIMAL)
+        self._write_test(['\\,', 'a'], '\\\\\\,,a',
+                         escapechar='\\', quoting=csv.QUOTE_NONE)
+        self._write_test([',\\', 'a'], '",\\\\",a',
+                         escapechar='\\', quoting=csv.QUOTE_MINIMAL)
+        self._write_test(['C\\', '6', '7', 'X"'], 'C\\\\,6,7,"X"""',
+                         escapechar='\\', quoting=csv.QUOTE_MINIMAL)
+
+    def test_write_lineterminator(self):
+        for lineterminator in '\r\n', '\n', '\r', '!@#', '\0':
+            with self.subTest(lineterminator=lineterminator):
+                with StringIO() as sio:
+                    writer = csv.writer(sio, lineterminator=lineterminator)
+                    writer.writerow(['a', 'b'])
+                    writer.writerow([1, 2])
+                    self.assertEqual(sio.getvalue(),
+                                     f'a,b{lineterminator}'
+                                     f'1,2{lineterminator}')
+
+    def test_write_iterable(self):
+        self._write_test(iter(['a', 1, 'p,q']), 'a,1,"p,q"')
+        self._write_test(iter(['a', 1, None]), 'a,1,')
+        self._write_test(iter([]), '')
+        self._write_test(iter([None]), '""')
+        self._write_error_test(csv.Error, iter([None]), quoting=csv.QUOTE_NONE)
+        self._write_test(iter([None, None]), ',')
+
+    def test_writerows(self):
+        class BrokenFile:
+            def write(self, buf):
+                raise OSError
+        writer = csv.writer(BrokenFile())
+        self.assertRaises(OSError, writer.writerows, [['a']])
+
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj)
+            self.assertRaises(TypeError, writer.writerows, None)
+            writer.writerows([['a', 'b'], ['c', 'd']])
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), "a,b\r\nc,d\r\n")
+
+    def test_writerows_with_none(self):
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj)
+            writer.writerows([['a', None], [None, 'd']])
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), "a,\r\n,d\r\n")
+
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj)
+            writer.writerows([[None], ['a']])
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), '""\r\na\r\n')
+
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj)
+            writer.writerows([['a'], [None]])
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), 'a\r\n""\r\n')
+
+    def test_writerows_errors(self):
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj)
+            self.assertRaises(TypeError, writer.writerows, None)
+            self.assertRaises(OSError, writer.writerows, BadIterable())
+
+    @support.cpython_only
+    @support.requires_legacy_unicode_capi()
+    @warnings_helper.ignore_warnings(category=DeprecationWarning)
+    def test_writerows_legacy_strings(self):
+        import _testcapi
+        c = _testcapi.unicode_legacy_string('a')
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj)
+            writer.writerows([[c]])
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), "a\r\n")
+
+    def _read_test(self, input, expect, **kwargs):
+        reader = csv.reader(input, **kwargs)
+        result = list(reader)
+        self.assertEqual(result, expect)
+
+    def test_read_oddinputs(self):
+        self._read_test([], [])
+        self._read_test([''], [[]])
+        self.assertRaises(csv.Error, self._read_test,
+                          ['"ab"c'], None, strict = 1)
+        self._read_test(['"ab"c'], [['abc']], doublequote = 0)
+
+        self.assertRaises(csv.Error, self._read_test,
+                          [b'abc'], None)
+
+    def test_read_eol(self):
+        self._read_test(['a,b'], [['a','b']])
+        self._read_test(['a,b\n'], [['a','b']])
+        self._read_test(['a,b\r\n'], [['a','b']])
+        self._read_test(['a,b\r'], [['a','b']])
+        self.assertRaises(csv.Error, self._read_test, ['a,b\rc,d'], [])
+        self.assertRaises(csv.Error, self._read_test, ['a,b\nc,d'], [])
+        self.assertRaises(csv.Error, self._read_test, ['a,b\r\nc,d'], [])
+
+    def test_read_eof(self):
+        self._read_test(['a,"'], [['a', '']])
+        self._read_test(['"a'], [['a']])
+        self._read_test(['^'], [['\n']], escapechar='^')
+        self.assertRaises(csv.Error, self._read_test, ['a,"'], [], strict=True)
+        self.assertRaises(csv.Error, self._read_test, ['"a'], [], strict=True)
+        self.assertRaises(csv.Error, self._read_test,
+                          ['^'], [], escapechar='^', strict=True)
+
+    def test_read_nul(self):
+        self._read_test(['\0'], [['\0']])
+        self._read_test(['a,\0b,c'], [['a', '\0b', 'c']])
+        self._read_test(['a,b\0,c'], [['a', 'b\0', 'c']])
+        self._read_test(['a,b\\\0,c'], [['a', 'b\0', 'c']], escapechar='\\')
+        self._read_test(['a,"\0b",c'], [['a', '\0b', 'c']])
+
+    def test_read_delimiter(self):
+        self._read_test(['a,b,c'], [['a', 'b', 'c']])
+        self._read_test(['a;b;c'], [['a', 'b', 'c']], delimiter=';')
+        self._read_test(['a\0b\0c'], [['a', 'b', 'c']], delimiter='\0')
+
+    def test_read_escape(self):
+        self._read_test(['a,\\b,c'], [['a', 'b', 'c']], escapechar='\\')
+        self._read_test(['a,b\\,c'], [['a', 'b,c']], escapechar='\\')
+        self._read_test(['a,"b\\,c"'], [['a', 'b,c']], escapechar='\\')
+        self._read_test(['a,"b,\\c"'], [['a', 'b,c']], escapechar='\\')
+        self._read_test(['a,"b,c\\""'], [['a', 'b,c"']], escapechar='\\')
+        self._read_test(['a,"b,c"\\'], [['a', 'b,c\\']], escapechar='\\')
+        self._read_test(['a,^b,c'], [['a', 'b', 'c']], escapechar='^')
+        self._read_test(['a,\0b,c'], [['a', 'b', 'c']], escapechar='\0')
+        self._read_test(['a,\\b,c'], [['a', '\\b', 'c']], escapechar=None)
+        self._read_test(['a,\\b,c'], [['a', '\\b', 'c']])
+
+    def test_read_quoting(self):
+        self._read_test(['1,",3,",5'], [['1', ',3,', '5']])
+        self._read_test(['1,",3,",5'], [['1', '"', '3', '"', '5']],
+                        quotechar=None, escapechar='\\')
+        self._read_test(['1,",3,",5'], [['1', '"', '3', '"', '5']],
+                        quoting=csv.QUOTE_NONE, escapechar='\\')
+        # will this fail where locale uses comma for decimals?
+        self._read_test([',3,"5",7.3, 9'], [['', 3, '5', 7.3, 9]],
+                        quoting=csv.QUOTE_NONNUMERIC)
+        self._read_test(['"a\nb", 7'], [['a\nb', ' 7']])
+        self.assertRaises(ValueError, self._read_test,
+                          ['abc,3'], [[]],
+                          quoting=csv.QUOTE_NONNUMERIC)
+        self._read_test(['1,@,3,@,5'], [['1', ',3,', '5']], quotechar='@')
+        self._read_test(['1,\0,3,\0,5'], [['1', ',3,', '5']], quotechar='\0')
+
+    def test_read_skipinitialspace(self):
+        self._read_test(['no space, space,  spaces,\ttab'],
+                        [['no space', 'space', 'spaces', '\ttab']],
+                        skipinitialspace=True)
+
+    def test_read_bigfield(self):
+        # This exercises the buffer realloc functionality and field size
+        # limits.
+        limit = csv.field_size_limit()
+        try:
+            size = 50000
+            bigstring = 'X' * size
+            bigline = '%s,%s' % (bigstring, bigstring)
+            self._read_test([bigline], [[bigstring, bigstring]])
+            csv.field_size_limit(size)
+            self._read_test([bigline], [[bigstring, bigstring]])
+            self.assertEqual(csv.field_size_limit(), size)
+            csv.field_size_limit(size-1)
+            self.assertRaises(csv.Error, self._read_test, [bigline], [])
+            self.assertRaises(TypeError, csv.field_size_limit, None)
+            self.assertRaises(TypeError, csv.field_size_limit, 1, None)
+        finally:
+            csv.field_size_limit(limit)
+
+    def test_read_linenum(self):
+        r = csv.reader(['line,1', 'line,2', 'line,3'])
+        self.assertEqual(r.line_num, 0)
+        next(r)
+        self.assertEqual(r.line_num, 1)
+        next(r)
+        self.assertEqual(r.line_num, 2)
+        next(r)
+        self.assertEqual(r.line_num, 3)
+        self.assertRaises(StopIteration, next, r)
+        self.assertEqual(r.line_num, 3)
+
+    def test_roundtrip_quoteed_newlines(self):
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj)
+            rows = [['a\nb','b'],['c','x\r\nd']]
+            writer.writerows(rows)
+            fileobj.seek(0)
+            for i, row in enumerate(csv.reader(fileobj)):
+                self.assertEqual(row, rows[i])
+
+    def test_roundtrip_escaped_unquoted_newlines(self):
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj,quoting=csv.QUOTE_NONE,escapechar="\\")
+            rows = [['a\nb','b'],['c','x\r\nd']]
+            writer.writerows(rows)
+            fileobj.seek(0)
+            for i, row in enumerate(csv.reader(fileobj,quoting=csv.QUOTE_NONE,escapechar="\\")):
+                self.assertEqual(row,rows[i])
+
+class TestDialectRegistry(unittest.TestCase):
+    def test_registry_badargs(self):
+        self.assertRaises(TypeError, csv.list_dialects, None)
+        self.assertRaises(TypeError, csv.get_dialect)
+        self.assertRaises(csv.Error, csv.get_dialect, None)
+        self.assertRaises(csv.Error, csv.get_dialect, "nonesuch")
+        self.assertRaises(TypeError, csv.unregister_dialect)
+        self.assertRaises(csv.Error, csv.unregister_dialect, None)
+        self.assertRaises(csv.Error, csv.unregister_dialect, "nonesuch")
+        self.assertRaises(TypeError, csv.register_dialect, None)
+        self.assertRaises(TypeError, csv.register_dialect, None, None)
+        self.assertRaises(TypeError, csv.register_dialect, "nonesuch", 0, 0)
+        self.assertRaises(TypeError, csv.register_dialect, "nonesuch",
+                          badargument=None)
+        self.assertRaises(TypeError, csv.register_dialect, "nonesuch",
+                          quoting=None)
+        self.assertRaises(TypeError, csv.register_dialect, [])
+
+    def test_registry(self):
+        class myexceltsv(csv.excel):
+            delimiter = "\t"
+        name = "myexceltsv"
+        expected_dialects = csv.list_dialects() + [name]
+        expected_dialects.sort()
+        csv.register_dialect(name, myexceltsv)
+        self.addCleanup(csv.unregister_dialect, name)
+        self.assertEqual(csv.get_dialect(name).delimiter, '\t')
+        got_dialects = sorted(csv.list_dialects())
+        self.assertEqual(expected_dialects, got_dialects)
+
+    def test_register_kwargs(self):
+        name = 'fedcba'
+        csv.register_dialect(name, delimiter=';')
+        self.addCleanup(csv.unregister_dialect, name)
+        self.assertEqual(csv.get_dialect(name).delimiter, ';')
+        self.assertEqual([['X', 'Y', 'Z']], list(csv.reader(['X;Y;Z'], name)))
+
+    def test_register_kwargs_override(self):
+        class mydialect(csv.Dialect):
+            delimiter = "\t"
+            quotechar = '"'
+            doublequote = True
+            skipinitialspace = False
+            lineterminator = '\r\n'
+            quoting = csv.QUOTE_MINIMAL
+
+        name = 'test_dialect'
+        csv.register_dialect(name, mydialect,
+                             delimiter=';',
+                             quotechar="'",
+                             doublequote=False,
+                             skipinitialspace=True,
+                             lineterminator='\n',
+                             quoting=csv.QUOTE_ALL)
+        self.addCleanup(csv.unregister_dialect, name)
+
+        # Ensure that kwargs do override attributes of a dialect class:
+        dialect = csv.get_dialect(name)
+        self.assertEqual(dialect.delimiter, ';')
+        self.assertEqual(dialect.quotechar, "'")
+        self.assertEqual(dialect.doublequote, False)
+        self.assertEqual(dialect.skipinitialspace, True)
+        self.assertEqual(dialect.lineterminator, '\n')
+        self.assertEqual(dialect.quoting, csv.QUOTE_ALL)
+
+    def test_incomplete_dialect(self):
+        class myexceltsv(csv.Dialect):
+            delimiter = "\t"
+        self.assertRaises(csv.Error, myexceltsv)
+
+    def test_space_dialect(self):
+        class space(csv.excel):
+            delimiter = " "
+            quoting = csv.QUOTE_NONE
+            escapechar = "\\"
+
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
+            fileobj.write("abc def\nc1ccccc1 benzene\n")
+            fileobj.seek(0)
+            reader = csv.reader(fileobj, dialect=space())
+            self.assertEqual(next(reader), ["abc", "def"])
+            self.assertEqual(next(reader), ["c1ccccc1", "benzene"])
+
+    def compare_dialect_123(self, expected, *writeargs, **kwwriteargs):
+
+        with TemporaryFile("w+", newline='', encoding="utf-8") as fileobj:
+
+            writer = csv.writer(fileobj, *writeargs, **kwwriteargs)
+            writer.writerow([1,2,3])
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), expected)
+
+    def test_dialect_apply(self):
+        class testA(csv.excel):
+            delimiter = "\t"
+        class testB(csv.excel):
+            delimiter = ":"
+        class testC(csv.excel):
+            delimiter = "|"
+        class testUni(csv.excel):
+            delimiter = "\u039B"
+
+        class unspecified():
+            # A class to pass as dialect but with no dialect attributes.
+            pass
+
+        csv.register_dialect('testC', testC)
+        try:
+            self.compare_dialect_123("1,2,3\r\n")
+            self.compare_dialect_123("1,2,3\r\n", dialect=None)
+            self.compare_dialect_123("1,2,3\r\n", dialect=unspecified)
+            self.compare_dialect_123("1\t2\t3\r\n", testA)
+            self.compare_dialect_123("1:2:3\r\n", dialect=testB())
+            self.compare_dialect_123("1|2|3\r\n", dialect='testC')
+            self.compare_dialect_123("1;2;3\r\n", dialect=testA,
+                                     delimiter=';')
+            self.compare_dialect_123("1\u039B2\u039B3\r\n",
+                                     dialect=testUni)
+
+        finally:
+            csv.unregister_dialect('testC')
+
+    def test_bad_dialect(self):
+        # Unknown parameter
+        self.assertRaises(TypeError, csv.reader, [], bad_attr = 0)
+        # Bad values
+        self.assertRaises(TypeError, csv.reader, [], delimiter = None)
+        self.assertRaises(TypeError, csv.reader, [], quoting = -1)
+        self.assertRaises(TypeError, csv.reader, [], quoting = 100)
+
+    def test_copy(self):
+        for name in csv.list_dialects():
+            dialect = csv.get_dialect(name)
+            self.assertRaises(TypeError, copy.copy, dialect)
+
+    def test_pickle(self):
+        for name in csv.list_dialects():
+            dialect = csv.get_dialect(name)
+            for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+                self.assertRaises(TypeError, pickle.dumps, dialect, proto)
+
+class TestCsvBase(unittest.TestCase):
+    def readerAssertEqual(self, input, expected_result):
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            fileobj.write(input)
+            fileobj.seek(0)
+            reader = csv.reader(fileobj, dialect = self.dialect)
+            fields = list(reader)
+            self.assertEqual(fields, expected_result)
+
+    def writerAssertEqual(self, input, expected_result):
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj, dialect = self.dialect)
+            writer.writerows(input)
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), expected_result)
+
+class TestDialectExcel(TestCsvBase):
+    dialect = 'excel'
+
+    def test_single(self):
+        self.readerAssertEqual('abc', [['abc']])
+
+    def test_simple(self):
+        self.readerAssertEqual('1,2,3,4,5', [['1','2','3','4','5']])
+
+    def test_blankline(self):
+        self.readerAssertEqual('', [])
+
+    def test_empty_fields(self):
+        self.readerAssertEqual(',', [['', '']])
+
+    def test_singlequoted(self):
+        self.readerAssertEqual('""', [['']])
+
+    def test_singlequoted_left_empty(self):
+        self.readerAssertEqual('"",', [['','']])
+
+    def test_singlequoted_right_empty(self):
+        self.readerAssertEqual(',""', [['','']])
+
+    def test_single_quoted_quote(self):
+        self.readerAssertEqual('""""', [['"']])
+
+    def test_quoted_quotes(self):
+        self.readerAssertEqual('""""""', [['""']])
+
+    def test_inline_quote(self):
+        self.readerAssertEqual('a""b', [['a""b']])
+
+    def test_inline_quotes(self):
+        self.readerAssertEqual('a"b"c', [['a"b"c']])
+
+    def test_quotes_and_more(self):
+        # Excel would never write a field containing '"a"b', but when
+        # reading one, it will return 'ab'.
+        self.readerAssertEqual('"a"b', [['ab']])
+
+    def test_lone_quote(self):
+        self.readerAssertEqual('a"b', [['a"b']])
+
+    def test_quote_and_quote(self):
+        # Excel would never write a field containing '"a" "b"', but when
+        # reading one, it will return 'a "b"'.
+        self.readerAssertEqual('"a" "b"', [['a "b"']])
+
+    def test_space_and_quote(self):
+        self.readerAssertEqual(' "a"', [[' "a"']])
+
+    def test_quoted(self):
+        self.readerAssertEqual('1,2,3,"I think, therefore I am",5,6',
+                               [['1', '2', '3',
+                                 'I think, therefore I am',
+                                 '5', '6']])
+
+    def test_quoted_quote(self):
+        self.readerAssertEqual('1,2,3,"""I see,"" said the blind man","as he picked up his hammer and saw"',
+                               [['1', '2', '3',
+                                 '"I see," said the blind man',
+                                 'as he picked up his hammer and saw']])
+
+    def test_quoted_nl(self):
+        input = '''\
+1,2,3,"""I see,""
+said the blind man","as he picked up his
+hammer and saw"
+9,8,7,6'''
+        self.readerAssertEqual(input,
+                               [['1', '2', '3',
+                                   '"I see,"\nsaid the blind man',
+                                   'as he picked up his\nhammer and saw'],
+                                ['9','8','7','6']])
+
+    def test_dubious_quote(self):
+        self.readerAssertEqual('12,12,1",', [['12', '12', '1"', '']])
+
+    def test_null(self):
+        self.writerAssertEqual([], '')
+
+    def test_single_writer(self):
+        self.writerAssertEqual([['abc']], 'abc\r\n')
+
+    def test_simple_writer(self):
+        self.writerAssertEqual([[1, 2, 'abc', 3, 4]], '1,2,abc,3,4\r\n')
+
+    def test_quotes(self):
+        self.writerAssertEqual([[1, 2, 'a"bc"', 3, 4]], '1,2,"a""bc""",3,4\r\n')
+
+    def test_quote_fieldsep(self):
+        self.writerAssertEqual([['abc,def']], '"abc,def"\r\n')
+
+    def test_newlines(self):
+        self.writerAssertEqual([[1, 2, 'a\nbc', 3, 4]], '1,2,"a\nbc",3,4\r\n')
+
+class EscapedExcel(csv.excel):
+    quoting = csv.QUOTE_NONE
+    escapechar = '\\'
+
+class TestEscapedExcel(TestCsvBase):
+    dialect = EscapedExcel()
+
+    def test_escape_fieldsep(self):
+        self.writerAssertEqual([['abc,def']], 'abc\\,def\r\n')
+
+    def test_read_escape_fieldsep(self):
+        self.readerAssertEqual('abc\\,def\r\n', [['abc,def']])
+
+class TestDialectUnix(TestCsvBase):
+    dialect = 'unix'
+
+    def test_simple_writer(self):
+        self.writerAssertEqual([[1, 'abc def', 'abc']], '"1","abc def","abc"\n')
+
+    def test_simple_reader(self):
+        self.readerAssertEqual('"1","abc def","abc"\n', [['1', 'abc def', 'abc']])
+
+class QuotedEscapedExcel(csv.excel):
+    quoting = csv.QUOTE_NONNUMERIC
+    escapechar = '\\'
+
+class TestQuotedEscapedExcel(TestCsvBase):
+    dialect = QuotedEscapedExcel()
+
+    def test_write_escape_fieldsep(self):
+        self.writerAssertEqual([['abc,def']], '"abc,def"\r\n')
+
+    def test_read_escape_fieldsep(self):
+        self.readerAssertEqual('"abc\\,def"\r\n', [['abc,def']])
+
+class TestDictFields(unittest.TestCase):
+    ### "long" means the row is longer than the number of fieldnames
+    ### "short" means there are fewer elements in the row than fieldnames
+    def test_writeheader_return_value(self):
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.DictWriter(fileobj, fieldnames = ["f1", "f2", "f3"])
+            writeheader_return_value = writer.writeheader()
+            self.assertEqual(writeheader_return_value, 10)
+
+    def test_write_simple_dict(self):
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.DictWriter(fileobj, fieldnames = ["f1", "f2", "f3"])
+            writer.writeheader()
+            fileobj.seek(0)
+            self.assertEqual(fileobj.readline(), "f1,f2,f3\r\n")
+            writer.writerow({"f1": 10, "f3": "abc"})
+            fileobj.seek(0)
+            fileobj.readline() # header
+            self.assertEqual(fileobj.read(), "10,,abc\r\n")
+
+    def test_write_multiple_dict_rows(self):
+        fileobj = StringIO()
+        writer = csv.DictWriter(fileobj, fieldnames=["f1", "f2", "f3"])
+        writer.writeheader()
+        self.assertEqual(fileobj.getvalue(), "f1,f2,f3\r\n")
+        writer.writerows([{"f1": 1, "f2": "abc", "f3": "f"},
+                          {"f1": 2, "f2": 5, "f3": "xyz"}])
+        self.assertEqual(fileobj.getvalue(),
+                         "f1,f2,f3\r\n1,abc,f\r\n2,5,xyz\r\n")
+
+    def test_write_no_fields(self):
+        fileobj = StringIO()
+        self.assertRaises(TypeError, csv.DictWriter, fileobj)
+
+    def test_write_fields_not_in_fieldnames(self):
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.DictWriter(fileobj, fieldnames = ["f1", "f2", "f3"])
+            # Of special note is the non-string key (issue 19449)
+            with self.assertRaises(ValueError) as cx:
+                writer.writerow({"f4": 10, "f2": "spam", 1: "abc"})
+            exception = str(cx.exception)
+            self.assertIn("fieldnames", exception)
+            self.assertIn("'f4'", exception)
+            self.assertNotIn("'f2'", exception)
+            self.assertIn("1", exception)
+
+    def test_typo_in_extrasaction_raises_error(self):
+        fileobj = StringIO()
+        self.assertRaises(ValueError, csv.DictWriter, fileobj, ['f1', 'f2'],
+                          extrasaction="raised")
+
+    def test_write_field_not_in_field_names_raise(self):
+        fileobj = StringIO()
+        writer = csv.DictWriter(fileobj, ['f1', 'f2'], extrasaction="raise")
+        dictrow = {'f0': 0, 'f1': 1, 'f2': 2, 'f3': 3}
+        self.assertRaises(ValueError, csv.DictWriter.writerow, writer, dictrow)
+
+        # see bpo-44512 (differently cased 'raise' should not result in 'ignore')
+        writer = csv.DictWriter(fileobj, ['f1', 'f2'], extrasaction="RAISE")
+        self.assertRaises(ValueError, csv.DictWriter.writerow, writer, dictrow)
+
+    def test_write_field_not_in_field_names_ignore(self):
+        fileobj = StringIO()
+        writer = csv.DictWriter(fileobj, ['f1', 'f2'], extrasaction="ignore")
+        dictrow = {'f0': 0, 'f1': 1, 'f2': 2, 'f3': 3}
+        csv.DictWriter.writerow(writer, dictrow)
+        self.assertEqual(fileobj.getvalue(), "1,2\r\n")
+
+        # bpo-44512
+        writer = csv.DictWriter(fileobj, ['f1', 'f2'], extrasaction="IGNORE")
+        csv.DictWriter.writerow(writer, dictrow)
+
+    def test_dict_reader_fieldnames_accepts_iter(self):
+        fieldnames = ["a", "b", "c"]
+        f = StringIO()
+        reader = csv.DictReader(f, iter(fieldnames))
+        self.assertEqual(reader.fieldnames, fieldnames)
+
+    def test_dict_reader_fieldnames_accepts_list(self):
+        fieldnames = ["a", "b", "c"]
+        f = StringIO()
+        reader = csv.DictReader(f, fieldnames)
+        self.assertEqual(reader.fieldnames, fieldnames)
+
+    def test_dict_writer_fieldnames_rejects_iter(self):
+        fieldnames = ["a", "b", "c"]
+        f = StringIO()
+        writer = csv.DictWriter(f, iter(fieldnames))
+        self.assertEqual(writer.fieldnames, fieldnames)
+
+    def test_dict_writer_fieldnames_accepts_list(self):
+        fieldnames = ["a", "b", "c"]
+        f = StringIO()
+        writer = csv.DictWriter(f, fieldnames)
+        self.assertEqual(writer.fieldnames, fieldnames)
+
+    def test_dict_reader_fieldnames_is_optional(self):
+        f = StringIO()
+        reader = csv.DictReader(f, fieldnames=None)
+
+    def test_read_dict_fields(self):
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
+            fileobj.write("1,2,abc\r\n")
+            fileobj.seek(0)
+            reader = csv.DictReader(fileobj,
+                                    fieldnames=["f1", "f2", "f3"])
+            self.assertEqual(next(reader), {"f1": '1', "f2": '2', "f3": 'abc'})
+
+    def test_read_dict_no_fieldnames(self):
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
+            fileobj.write("f1,f2,f3\r\n1,2,abc\r\n")
+            fileobj.seek(0)
+            reader = csv.DictReader(fileobj)
+            self.assertEqual(next(reader), {"f1": '1', "f2": '2', "f3": 'abc'})
+            self.assertEqual(reader.fieldnames, ["f1", "f2", "f3"])
+
+    # Two test cases to make sure existing ways of implicitly setting
+    # fieldnames continue to work.  Both arise from discussion in issue3436.
+    def test_read_dict_fieldnames_from_file(self):
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
+            fileobj.write("f1,f2,f3\r\n1,2,abc\r\n")
+            fileobj.seek(0)
+            reader = csv.DictReader(fileobj,
+                                    fieldnames=next(csv.reader(fileobj)))
+            self.assertEqual(reader.fieldnames, ["f1", "f2", "f3"])
+            self.assertEqual(next(reader), {"f1": '1', "f2": '2', "f3": 'abc'})
+
+    def test_read_dict_fieldnames_chain(self):
+        import itertools
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
+            fileobj.write("f1,f2,f3\r\n1,2,abc\r\n")
+            fileobj.seek(0)
+            reader = csv.DictReader(fileobj)
+            first = next(reader)
+            for row in itertools.chain([first], reader):
+                self.assertEqual(reader.fieldnames, ["f1", "f2", "f3"])
+                self.assertEqual(row, {"f1": '1', "f2": '2', "f3": 'abc'})
+
+    def test_read_long(self):
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
+            fileobj.write("1,2,abc,4,5,6\r\n")
+            fileobj.seek(0)
+            reader = csv.DictReader(fileobj,
+                                    fieldnames=["f1", "f2"])
+            self.assertEqual(next(reader), {"f1": '1', "f2": '2',
+                                             None: ["abc", "4", "5", "6"]})
+
+    def test_read_long_with_rest(self):
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
+            fileobj.write("1,2,abc,4,5,6\r\n")
+            fileobj.seek(0)
+            reader = csv.DictReader(fileobj,
+                                    fieldnames=["f1", "f2"], restkey="_rest")
+            self.assertEqual(next(reader), {"f1": '1', "f2": '2',
+                                             "_rest": ["abc", "4", "5", "6"]})
+
+    def test_read_long_with_rest_no_fieldnames(self):
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
+            fileobj.write("f1,f2\r\n1,2,abc,4,5,6\r\n")
+            fileobj.seek(0)
+            reader = csv.DictReader(fileobj, restkey="_rest")
+            self.assertEqual(reader.fieldnames, ["f1", "f2"])
+            self.assertEqual(next(reader), {"f1": '1', "f2": '2',
+                                             "_rest": ["abc", "4", "5", "6"]})
+
+    def test_read_short(self):
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
+            fileobj.write("1,2,abc,4,5,6\r\n1,2,abc\r\n")
+            fileobj.seek(0)
+            reader = csv.DictReader(fileobj,
+                                    fieldnames="1 2 3 4 5 6".split(),
+                                    restval="DEFAULT")
+            self.assertEqual(next(reader), {"1": '1', "2": '2', "3": 'abc',
+                                             "4": '4', "5": '5', "6": '6'})
+            self.assertEqual(next(reader), {"1": '1', "2": '2', "3": 'abc',
+                                             "4": 'DEFAULT', "5": 'DEFAULT',
+                                             "6": 'DEFAULT'})
+
+    def test_read_multi(self):
+        sample = [
+            '2147483648,43.0e12,17,abc,def\r\n',
+            '147483648,43.0e2,17,abc,def\r\n',
+            '47483648,43.0,170,abc,def\r\n'
+            ]
+
+        reader = csv.DictReader(sample,
+                                fieldnames="i1 float i2 s1 s2".split())
+        self.assertEqual(next(reader), {"i1": '2147483648',
+                                         "float": '43.0e12',
+                                         "i2": '17',
+                                         "s1": 'abc',
+                                         "s2": 'def'})
+
+    def test_read_with_blanks(self):
+        reader = csv.DictReader(["1,2,abc,4,5,6\r\n","\r\n",
+                                 "1,2,abc,4,5,6\r\n"],
+                                fieldnames="1 2 3 4 5 6".split())
+        self.assertEqual(next(reader), {"1": '1', "2": '2', "3": 'abc',
+                                         "4": '4', "5": '5', "6": '6'})
+        self.assertEqual(next(reader), {"1": '1', "2": '2', "3": 'abc',
+                                         "4": '4', "5": '5', "6": '6'})
+
+    def test_read_semi_sep(self):
+        reader = csv.DictReader(["1;2;abc;4;5;6\r\n"],
+                                fieldnames="1 2 3 4 5 6".split(),
+                                delimiter=';')
+        self.assertEqual(next(reader), {"1": '1', "2": '2', "3": 'abc',
+                                         "4": '4', "5": '5', "6": '6'})
+
+class TestArrayWrites(unittest.TestCase):
+    def test_int_write(self):
+        import array
+        contents = [(20-i) for i in range(20)]
+        a = array.array('i', contents)
+
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj, dialect="excel")
+            writer.writerow(a)
+            expected = ",".join([str(i) for i in a])+"\r\n"
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), expected)
+
+    def test_double_write(self):
+        import array
+        contents = [(20-i)*0.1 for i in range(20)]
+        a = array.array('d', contents)
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj, dialect="excel")
+            writer.writerow(a)
+            expected = ",".join([str(i) for i in a])+"\r\n"
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), expected)
+
+    def test_float_write(self):
+        import array
+        contents = [(20-i)*0.1 for i in range(20)]
+        a = array.array('f', contents)
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj, dialect="excel")
+            writer.writerow(a)
+            expected = ",".join([str(i) for i in a])+"\r\n"
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), expected)
+
+    def test_char_write(self):
+        import array, string
+        a = array.array('u', string.ascii_letters)
+
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
+            writer = csv.writer(fileobj, dialect="excel")
+            writer.writerow(a)
+            expected = ",".join(a)+"\r\n"
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), expected)
+
+class TestDialectValidity(unittest.TestCase):
+    def test_quoting(self):
+        class mydialect(csv.Dialect):
+            delimiter = ";"
+            escapechar = '\\'
+            doublequote = False
+            skipinitialspace = True
+            lineterminator = '\r\n'
+            quoting = csv.QUOTE_NONE
+        d = mydialect()
+        self.assertEqual(d.quoting, csv.QUOTE_NONE)
+
+        mydialect.quoting = None
+        self.assertRaises(csv.Error, mydialect)
+
+        mydialect.doublequote = True
+        mydialect.quoting = csv.QUOTE_ALL
+        mydialect.quotechar = '"'
+        d = mydialect()
+        self.assertEqual(d.quoting, csv.QUOTE_ALL)
+        self.assertEqual(d.quotechar, '"')
+        self.assertTrue(d.doublequote)
+
+        mydialect.quotechar = ""
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"quotechar" must be a 1-character string')
+
+        mydialect.quotechar = "''"
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"quotechar" must be a 1-character string')
+
+        mydialect.quotechar = 4
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"quotechar" must be string or None, not int')
+
+    def test_delimiter(self):
+        class mydialect(csv.Dialect):
+            delimiter = ";"
+            escapechar = '\\'
+            doublequote = False
+            skipinitialspace = True
+            lineterminator = '\r\n'
+            quoting = csv.QUOTE_NONE
+        d = mydialect()
+        self.assertEqual(d.delimiter, ";")
+
+        mydialect.delimiter = ":::"
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"delimiter" must be a 1-character string')
+
+        mydialect.delimiter = ""
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"delimiter" must be a 1-character string')
+
+        mydialect.delimiter = b","
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"delimiter" must be string, not bytes')
+
+        mydialect.delimiter = 4
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"delimiter" must be string, not int')
+
+        mydialect.delimiter = None
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"delimiter" must be string, not NoneType')
+
+    def test_escapechar(self):
+        class mydialect(csv.Dialect):
+            delimiter = ";"
+            escapechar = '\\'
+            doublequote = False
+            skipinitialspace = True
+            lineterminator = '\r\n'
+            quoting = csv.QUOTE_NONE
+        d = mydialect()
+        self.assertEqual(d.escapechar, "\\")
+
+        mydialect.escapechar = ""
+        with self.assertRaisesRegex(csv.Error, '"escapechar" must be a 1-character string'):
+            mydialect()
+
+        mydialect.escapechar = "**"
+        with self.assertRaisesRegex(csv.Error, '"escapechar" must be a 1-character string'):
+            mydialect()
+
+        mydialect.escapechar = b"*"
+        with self.assertRaisesRegex(csv.Error, '"escapechar" must be string or None, not bytes'):
+            mydialect()
+
+        mydialect.escapechar = 4
+        with self.assertRaisesRegex(csv.Error, '"escapechar" must be string or None, not int'):
+            mydialect()
+
+    def test_lineterminator(self):
+        class mydialect(csv.Dialect):
+            delimiter = ";"
+            escapechar = '\\'
+            doublequote = False
+            skipinitialspace = True
+            lineterminator = '\r\n'
+            quoting = csv.QUOTE_NONE
+        d = mydialect()
+        self.assertEqual(d.lineterminator, '\r\n')
+
+        mydialect.lineterminator = ":::"
+        d = mydialect()
+        self.assertEqual(d.lineterminator, ":::")
+
+        mydialect.lineterminator = 4
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"lineterminator" must be a string')
+
+    def test_invalid_chars(self):
+        def create_invalid(field_name, value):
+            class mydialect(csv.Dialect):
+                pass
+            setattr(mydialect, field_name, value)
+            d = mydialect()
+
+        for field_name in ("delimiter", "escapechar", "quotechar"):
+            with self.subTest(field_name=field_name):
+                self.assertRaises(csv.Error, create_invalid, field_name, "")
+                self.assertRaises(csv.Error, create_invalid, field_name, "abc")
+                self.assertRaises(csv.Error, create_invalid, field_name, b'x')
+                self.assertRaises(csv.Error, create_invalid, field_name, 5)
+
+
+class TestSniffer(unittest.TestCase):
+    sample1 = """\
+Harry's, Arlington Heights, IL, 2/1/03, Kimi Hayes
+Shark City, Glendale Heights, IL, 12/28/02, Prezence
+Tommy's Place, Blue Island, IL, 12/28/02, Blue Sunday/White Crow
+Stonecutters Seafood and Chop House, Lemont, IL, 12/19/02, Week Back
+"""
+    sample2 = """\
+'Harry''s':'Arlington Heights':'IL':'2/1/03':'Kimi Hayes'
+'Shark City':'Glendale Heights':'IL':'12/28/02':'Prezence'
+'Tommy''s Place':'Blue Island':'IL':'12/28/02':'Blue Sunday/White Crow'
+'Stonecutters ''Seafood'' and Chop House':'Lemont':'IL':'12/19/02':'Week Back'
+"""
+    header1 = '''\
+"venue","city","state","date","performers"
+'''
+    sample3 = '''\
+05/05/03?05/05/03?05/05/03?05/05/03?05/05/03?05/05/03
+05/05/03?05/05/03?05/05/03?05/05/03?05/05/03?05/05/03
+05/05/03?05/05/03?05/05/03?05/05/03?05/05/03?05/05/03
+'''
+
+    sample4 = '''\
+2147483648;43.0e12;17;abc;def
+147483648;43.0e2;17;abc;def
+47483648;43.0;170;abc;def
+'''
+
+    sample5 = "aaa\tbbb\r\nAAA\t\r\nBBB\t\r\n"
+    sample6 = "a|b|c\r\nd|e|f\r\n"
+    sample7 = "'a'|'b'|'c'\r\n'd'|e|f\r\n"
+
+# Issue 18155: Use a delimiter that is a special char to regex:
+
+    header2 = '''\
+"venue"+"city"+"state"+"date"+"performers"
+'''
+    sample8 = """\
+Harry's+ Arlington Heights+ IL+ 2/1/03+ Kimi Hayes
+Shark City+ Glendale Heights+ IL+ 12/28/02+ Prezence
+Tommy's Place+ Blue Island+ IL+ 12/28/02+ Blue Sunday/White Crow
+Stonecutters Seafood and Chop House+ Lemont+ IL+ 12/19/02+ Week Back
+"""
+    sample9 = """\
+'Harry''s'+ Arlington Heights'+ 'IL'+ '2/1/03'+ 'Kimi Hayes'
+'Shark City'+ Glendale Heights'+' IL'+ '12/28/02'+ 'Prezence'
+'Tommy''s Place'+ Blue Island'+ 'IL'+ '12/28/02'+ 'Blue Sunday/White Crow'
+'Stonecutters ''Seafood'' and Chop House'+ 'Lemont'+ 'IL'+ '12/19/02'+ 'Week Back'
+"""
+
+    sample10 = dedent("""
+                        abc,def
+                        ghijkl,mno
+                        ghi,jkl
+                        """)
+
+    sample11 = dedent("""
+                        abc,def
+                        ghijkl,mnop
+                        ghi,jkl
+                         """)
+
+    sample12 = dedent(""""time","forces"
+                        1,1.5
+                        0.5,5+0j
+                        0,0
+                        1+1j,6
+                        """)
+
+    sample13 = dedent(""""time","forces"
+                        0,0
+                        1,2
+                        a,b
+                        """)
+
+    sample14 = """\
+abc\0def
+ghijkl\0mno
+ghi\0jkl
+"""
+
+    def test_issue43625(self):
+        sniffer = csv.Sniffer()
+        self.assertTrue(sniffer.has_header(self.sample12))
+        self.assertFalse(sniffer.has_header(self.sample13))
+
+    def test_has_header_strings(self):
+        "More to document existing (unexpected?) behavior than anything else."
+        sniffer = csv.Sniffer()
+        self.assertFalse(sniffer.has_header(self.sample10))
+        self.assertFalse(sniffer.has_header(self.sample11))
+
+    def test_has_header(self):
+        sniffer = csv.Sniffer()
+        self.assertIs(sniffer.has_header(self.sample1), False)
+        self.assertIs(sniffer.has_header(self.header1 + self.sample1), True)
+
+    def test_has_header_regex_special_delimiter(self):
+        sniffer = csv.Sniffer()
+        self.assertIs(sniffer.has_header(self.sample8), False)
+        self.assertIs(sniffer.has_header(self.header2 + self.sample8), True)
+
+    def test_guess_quote_and_delimiter(self):
+        sniffer = csv.Sniffer()
+        for header in (";'123;4';", "'123;4';", ";'123;4'", "'123;4'"):
+            with self.subTest(header):
+                dialect = sniffer.sniff(header, ",;")
+                self.assertEqual(dialect.delimiter, ';')
+                self.assertEqual(dialect.quotechar, "'")
+                self.assertIs(dialect.doublequote, False)
+                self.assertIs(dialect.skipinitialspace, False)
+
+    def test_sniff(self):
+        sniffer = csv.Sniffer()
+        dialect = sniffer.sniff(self.sample1)
+        self.assertEqual(dialect.delimiter, ",")
+        self.assertEqual(dialect.quotechar, '"')
+        self.assertIs(dialect.skipinitialspace, True)
+
+        dialect = sniffer.sniff(self.sample2)
+        self.assertEqual(dialect.delimiter, ":")
+        self.assertEqual(dialect.quotechar, "'")
+        self.assertIs(dialect.skipinitialspace, False)
+
+    def test_delimiters(self):
+        sniffer = csv.Sniffer()
+        dialect = sniffer.sniff(self.sample3)
+        # given that all three lines in sample3 are equal,
+        # I think that any character could have been 'guessed' as the
+        # delimiter, depending on dictionary order
+        self.assertIn(dialect.delimiter, self.sample3)
+        dialect = sniffer.sniff(self.sample3, delimiters="?,")
+        self.assertEqual(dialect.delimiter, "?")
+        dialect = sniffer.sniff(self.sample3, delimiters="/,")
+        self.assertEqual(dialect.delimiter, "/")
+        dialect = sniffer.sniff(self.sample4)
+        self.assertEqual(dialect.delimiter, ";")
+        dialect = sniffer.sniff(self.sample5)
+        self.assertEqual(dialect.delimiter, "\t")
+        dialect = sniffer.sniff(self.sample6)
+        self.assertEqual(dialect.delimiter, "|")
+        dialect = sniffer.sniff(self.sample7)
+        self.assertEqual(dialect.delimiter, "|")
+        self.assertEqual(dialect.quotechar, "'")
+        dialect = sniffer.sniff(self.sample8)
+        self.assertEqual(dialect.delimiter, '+')
+        dialect = sniffer.sniff(self.sample9)
+        self.assertEqual(dialect.delimiter, '+')
+        self.assertEqual(dialect.quotechar, "'")
+        dialect = sniffer.sniff(self.sample14)
+        self.assertEqual(dialect.delimiter, '\0')
+
+    def test_doublequote(self):
+        sniffer = csv.Sniffer()
+        dialect = sniffer.sniff(self.header1)
+        self.assertFalse(dialect.doublequote)
+        dialect = sniffer.sniff(self.header2)
+        self.assertFalse(dialect.doublequote)
+        dialect = sniffer.sniff(self.sample2)
+        self.assertTrue(dialect.doublequote)
+        dialect = sniffer.sniff(self.sample8)
+        self.assertFalse(dialect.doublequote)
+        dialect = sniffer.sniff(self.sample9)
+        self.assertTrue(dialect.doublequote)
+
+class NUL:
+    def write(s, *args):
+        pass
+    writelines = write
+
+@unittest.skipUnless(hasattr(sys, "gettotalrefcount"),
+                     'requires sys.gettotalrefcount()')
+class TestLeaks(unittest.TestCase):
+    def test_create_read(self):
+        delta = 0
+        lastrc = sys.gettotalrefcount()
+        for i in range(20):
+            gc.collect()
+            self.assertEqual(gc.garbage, [])
+            rc = sys.gettotalrefcount()
+            csv.reader(["a,b,c\r\n"])
+            csv.reader(["a,b,c\r\n"])
+            csv.reader(["a,b,c\r\n"])
+            delta = rc-lastrc
+            lastrc = rc
+        # if csv.reader() leaks, last delta should be 3 or more
+        self.assertLess(delta, 3)
+
+    def test_create_write(self):
+        delta = 0
+        lastrc = sys.gettotalrefcount()
+        s = NUL()
+        for i in range(20):
+            gc.collect()
+            self.assertEqual(gc.garbage, [])
+            rc = sys.gettotalrefcount()
+            csv.writer(s)
+            csv.writer(s)
+            csv.writer(s)
+            delta = rc-lastrc
+            lastrc = rc
+        # if csv.writer() leaks, last delta should be 3 or more
+        self.assertLess(delta, 3)
+
+    def test_read(self):
+        delta = 0
+        rows = ["a,b,c\r\n"]*5
+        lastrc = sys.gettotalrefcount()
+        for i in range(20):
+            gc.collect()
+            self.assertEqual(gc.garbage, [])
+            rc = sys.gettotalrefcount()
+            rdr = csv.reader(rows)
+            for row in rdr:
+                pass
+            delta = rc-lastrc
+            lastrc = rc
+        # if reader leaks during read, delta should be 5 or more
+        self.assertLess(delta, 5)
+
+    def test_write(self):
+        delta = 0
+        rows = [[1,2,3]]*5
+        s = NUL()
+        lastrc = sys.gettotalrefcount()
+        for i in range(20):
+            gc.collect()
+            self.assertEqual(gc.garbage, [])
+            rc = sys.gettotalrefcount()
+            writer = csv.writer(s)
+            for row in rows:
+                writer.writerow(row)
+            delta = rc-lastrc
+            lastrc = rc
+        # if writer leaks during write, last delta should be 5 or more
+        self.assertLess(delta, 5)
+
+class TestUnicode(unittest.TestCase):
+
+    names = ["Martin von Löwis",
+             "Marc André Lemburg",
+             "Guido van Rossum",
+             "François Pinard"]
+
+    def test_unicode_read(self):
+        with TemporaryFile("w+", newline='', encoding="utf-8") as fileobj:
+            fileobj.write(",".join(self.names) + "\r\n")
+            fileobj.seek(0)
+            reader = csv.reader(fileobj)
+            self.assertEqual(list(reader), [self.names])
+
+
+    def test_unicode_write(self):
+        with TemporaryFile("w+", newline='', encoding="utf-8") as fileobj:
+            writer = csv.writer(fileobj)
+            writer.writerow(self.names)
+            expected = ",".join(self.names)+"\r\n"
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), expected)
+
+class KeyOrderingTest(unittest.TestCase):
+
+    def test_ordering_for_the_dict_reader_and_writer(self):
+        resultset = set()
+        for keys in permutations("abcde"):
+            with TemporaryFile('w+', newline='', encoding="utf-8") as fileobject:
+                dw = csv.DictWriter(fileobject, keys)
+                dw.writeheader()
+                fileobject.seek(0)
+                dr = csv.DictReader(fileobject)
+                kt = tuple(dr.fieldnames)
+                self.assertEqual(keys, kt)
+                resultset.add(kt)
+        # Final sanity check: were all permutations unique?
+        self.assertEqual(len(resultset), 120, "Key ordering: some key permutations not collected (expected 120)")
+
+    def test_ordered_dict_reader(self):
+        data = dedent('''\
+            FirstName,LastName
+            Eric,Idle
+            Graham,Chapman,Over1,Over2
+
+            Under1
+            John,Cleese
+        ''').splitlines()
+
+        self.assertEqual(list(csv.DictReader(data)),
+            [OrderedDict([('FirstName', 'Eric'), ('LastName', 'Idle')]),
+             OrderedDict([('FirstName', 'Graham'), ('LastName', 'Chapman'),
+                          (None, ['Over1', 'Over2'])]),
+             OrderedDict([('FirstName', 'Under1'), ('LastName', None)]),
+             OrderedDict([('FirstName', 'John'), ('LastName', 'Cleese')]),
+            ])
+
+        self.assertEqual(list(csv.DictReader(data, restkey='OtherInfo')),
+            [OrderedDict([('FirstName', 'Eric'), ('LastName', 'Idle')]),
+             OrderedDict([('FirstName', 'Graham'), ('LastName', 'Chapman'),
+                          ('OtherInfo', ['Over1', 'Over2'])]),
+             OrderedDict([('FirstName', 'Under1'), ('LastName', None)]),
+             OrderedDict([('FirstName', 'John'), ('LastName', 'Cleese')]),
+            ])
+
+        del data[0]            # Remove the header row
+        self.assertEqual(list(csv.DictReader(data, fieldnames=['fname', 'lname'])),
+            [OrderedDict([('fname', 'Eric'), ('lname', 'Idle')]),
+             OrderedDict([('fname', 'Graham'), ('lname', 'Chapman'),
+                          (None, ['Over1', 'Over2'])]),
+             OrderedDict([('fname', 'Under1'), ('lname', None)]),
+             OrderedDict([('fname', 'John'), ('lname', 'Cleese')]),
+            ])
+
+
+class MiscTestCase(unittest.TestCase):
+    def test__all__(self):
+        extra = {'__doc__', '__version__'}
+        support.check__all__(self, csv, ('csv', '_csv'), extra=extra)
+
+    def test_subclassable(self):
+        # issue 44089
+        class Foo(csv.Error): ...
+
+    @support.cpython_only
+    def test_disallow_instantiation(self):
+        _csv = import_helper.import_module("_csv")
+        for tp in _csv.Reader, _csv.Writer:
+            with self.subTest(tp=tp):
+                check_disallow_instantiation(self, tp)
+
+if __name__ == '__main__':
+    unittest.main()