#
# Copyright 2009 Google Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Unit tests for fake_open.FakeOsModule."""

import errno
import io
import os
import stat
import sys
import time
import unittest

from pyfakefs import fake_filesystem, helpers
from pyfakefs.helpers import is_root, IS_PYPY, get_locale_encoding
from pyfakefs.fake_io import FakeIoModule
from pyfakefs.fake_filesystem_unittest import PatchMode, Patcher
from pyfakefs.tests.skipped_pathlib import read_open
from pyfakefs.tests.test_utils import RealFsTestCase, skip_if_symlink_not_supported


class FakeFileOpenTestBase(RealFsTestCase):
    def setUp(self):
        super().setUp()
        if self.use_real_fs():
            self.open = io.open
        else:
            self.fake_io_module = FakeIoModule(self.filesystem)
            self.open = self.fake_io_module.open

    def path_separator(self):
        return "!"


class FakeFileOpenTest(FakeFileOpenTestBase):
    def setUp(self):
        super().setUp()
        self.orig_time = time.time

    def tearDown(self):
        super().tearDown()
        time.time = self.orig_time

    def test_open_no_parent_dir(self):
        """Expect raise when opening a file in a missing directory."""
        file_path = self.make_path("foo", "bar.txt")
        self.assert_raises_os_error(errno.ENOENT, self.open, file_path, "w")

    def test_delete_on_close(self):
        self.skip_real_fs()
        file_dir = "boo"
        file_path = "boo!far"
        self.os.mkdir(file_dir)
        self.open = fake_filesystem.FakeFileOpen(self.filesystem, delete_on_close=True)
        with self.open(file_path, "w", encoding="utf8"):
            self.assertTrue(self.filesystem.exists(file_path))
        self.assertFalse(self.filesystem.exists(file_path))

    def test_no_delete_on_close_by_default(self):
        file_path = self.make_path("czar")
        with self.open(file_path, "w", encoding="utf8"):
            self.assertTrue(self.os.path.exists(file_path))
        self.assertTrue(self.os.path.exists(file_path))

    def test_compatibility_of_with_statement(self):
        self.skip_real_fs()
        self.open = fake_filesystem.FakeFileOpen(self.filesystem, delete_on_close=True)
        file_path = "foo"
        self.assertFalse(self.os.path.exists(file_path))
        with self.open(file_path, "w", encoding="utf8"):
            self.assertTrue(self.os.path.exists(file_path))
        # After the 'with' statement, the close() method should have been
        # called.
        self.assertFalse(self.os.path.exists(file_path))

    def test_unicode_contents(self):
        file_path = self.make_path("foo")
        # note that this will work only if the string can be represented
        # by the locale preferred encoding - which under Windows is
        # usually not UTF-8, but something like Latin1, depending on the locale
        text_fractions = "Ümläüts"
        try:
            with self.open(file_path, "w", encoding=get_locale_encoding()) as f:
                f.write(text_fractions)
        except UnicodeEncodeError:
            # see https://github.com/pytest-dev/pyfakefs/issues/623
            self.skipTest("This test does not work with an ASCII locale")

        with self.open(file_path, encoding=get_locale_encoding()) as f:
            contents = f.read()
        self.assertEqual(contents, text_fractions)

    def test_byte_contents(self):
        file_path = self.make_path("foo")
        byte_fractions = b"\xe2\x85\x93 \xe2\x85\x94 \xe2\x85\x95 \xe2\x85\x96"
        with self.open(file_path, "wb") as f:
            f.write(byte_fractions)
        # the encoding has to be specified, otherwise the locale default
        # is used which can be different on different systems
        with self.open(file_path, encoding="utf-8") as f:
            contents = f.read()
        self.assertEqual(contents, byte_fractions.decode("utf-8"))

    def test_write_str_read_bytes(self):
        file_path = self.make_path("foo")
        str_contents = "Äsgül"
        try:
            with self.open(file_path, "w", encoding=get_locale_encoding()) as f:
                f.write(str_contents)
            with self.open(file_path, "rb") as f:
                contents = f.read()
            self.assertEqual(str_contents, contents.decode(get_locale_encoding()))
        except UnicodeError:
            # see https://github.com/pytest-dev/pyfakefs/issues/623
            self.skipTest("This test does not work with an ASCII locale")

    def test_open_valid_file(self):
        contents = [
            "I am he as\n",
            "you are he as\n",
            "you are me and\n",
            "we are all together\n",
        ]
        file_path = self.make_path("bar.txt")
        self.create_file(file_path, contents="".join(contents))
        with self.open(file_path, encoding="utf8") as fake_file:
            self.assertEqual(contents, fake_file.readlines())

    def test_open_valid_args(self):
        contents = [
            "Bang bang Maxwell's silver hammer\n",
            "Came down on her head",
        ]
        file_path = self.make_path("abbey_road", "maxwell")
        self.create_file(file_path, contents="".join(contents))

        with self.open(file_path, encoding="utf8", buffering=1) as f:
            self.assertEqual(contents, f.readlines())
        with self.open(
            file_path,
            encoding="utf8",
            buffering=1,
            errors="strict",
            newline="\n",
            opener=None,
        ) as f:
            expected_contents = [
                contents[0][:-1] + self.os.linesep,
                contents[1],
            ]
            self.assertEqual(expected_contents, f.readlines())

    def test_open_valid_file_with_cwd(self):
        contents = [
            "I am he as\n",
            "you are he as\n",
            "you are me and\n",
            "we are all together\n",
        ]
        file_path = self.make_path("bar.txt")
        self.create_file(file_path, contents="".join(contents))
        self.os.chdir(self.base_path)
        with self.open(file_path, encoding="utf8") as f:
            self.assertEqual(contents, f.readlines())

    def test_iterate_over_file(self):
        contents = [
            "Bang bang Maxwell's silver hammer",
            "Came down on her head",
        ]
        file_path = self.make_path("abbey_road", "maxwell")
        self.create_file(file_path, contents="\n".join(contents))
        with self.open(file_path, encoding="utf8") as fake_file:
            result = [line.rstrip() for line in fake_file]
        self.assertEqual(contents, result)

    def test_next_over_file(self):
        contents = ["Live long\n", "and prosper\n"]
        result = []
        file_path = self.make_path("foo.txt")
        self.create_file(file_path, contents="".join(contents))
        with self.open(file_path, encoding="utf8") as fake_file:
            result.append(next(fake_file))
            result.append(next(fake_file))
        self.assertEqual(contents, result)

    def test_open_directory_error(self):
        directory_path = self.make_path("foo")
        self.os.mkdir(directory_path)
        if self.is_windows:
            self.assert_raises_os_error(
                errno.EACCES, self.open.__call__, directory_path
            )
        else:
            self.assert_raises_os_error(
                errno.EISDIR, self.open.__call__, directory_path
            )

    def test_create_file_with_write(self):
        contents = [
            "Here comes the sun, little darlin'",
            "Here comes the sun, and I say,",
            "It's alright",
        ]
        file_dir = self.make_path("abbey_road")
        file_path = self.os.path.join(file_dir, "here_comes_the_sun")
        self.os.mkdir(file_dir)
        with self.open(file_path, "w", encoding="utf8") as fake_file:
            for line in contents:
                fake_file.write(line + "\n")
        with self.open(file_path, encoding="utf8") as fake_file:
            result = [line.rstrip() for line in fake_file]
        self.assertEqual(contents, result)

    def test_create_file_with_append(self):
        contents = [
            "Here comes the sun, little darlin'",
            "Here comes the sun, and I say,",
            "It's alright",
        ]
        file_dir = self.make_path("abbey_road")
        file_path = self.os.path.join(file_dir, "here_comes_the_sun")
        self.os.mkdir(file_dir)
        with self.open(file_path, "a", encoding="utf8") as fake_file:
            for line in contents:
                fake_file.write(line + "\n")
        with self.open(file_path, encoding="utf8") as fake_file:
            result = [line.rstrip() for line in fake_file]
        self.assertEqual(contents, result)

    def test_exclusive_create_file_failure(self):
        skip_if_symlink_not_supported()
        file_path = self.make_path("bar")
        self.create_file(file_path)
        self.assert_raises_os_error(errno.EEXIST, self.open, file_path, "x")
        self.assert_raises_os_error(errno.EEXIST, self.open, file_path, "xb")

    def test_exclusive_create_file(self):
        file_dir = self.make_path("foo")
        file_path = self.os.path.join(file_dir, "bar")
        self.os.mkdir(file_dir)
        contents = "String contents"
        with self.open(file_path, "x", encoding="utf8") as fake_file:
            fake_file.write(contents)
        with self.open(file_path, encoding="utf8") as fake_file:
            self.assertEqual(contents, fake_file.read())

    def test_exclusive_create_binary_file(self):
        file_dir = self.make_path("foo")
        file_path = self.os.path.join(file_dir, "bar")
        self.os.mkdir(file_dir)
        contents = b"Binary contents"
        with self.open(file_path, "xb") as fake_file:
            self.assertEqual("xb", fake_file.mode)
            fake_file.write(contents)
        with self.open(file_path, "rb") as fake_file:
            self.assertEqual("rb", fake_file.mode)
            self.assertEqual(contents, fake_file.read())

    def test_overwrite_existing_file(self):
        file_path = self.make_path("overwrite")
        self.create_file(file_path, contents="To disappear")
        new_contents = [
            "Only these lines",
            "should be in the file.",
        ]
        with self.open(file_path, "w", encoding="utf8") as fake_file:
            for line in new_contents:
                fake_file.write(line + "\n")
        with self.open(file_path, encoding="utf8") as fake_file:
            result = [line.rstrip() for line in fake_file]
        self.assertEqual(new_contents, result)

    def test_append_existing_file(self):
        file_path = self.make_path("appendfile")
        contents = [
            "Contents of original fileAppended contents",
        ]

        self.create_file(file_path, contents=contents[0])
        with self.open(file_path, "a", encoding="utf8") as fake_file:
            for line in contents[1:]:
                fake_file.write(line + "\n")
        with self.open(file_path, encoding="utf8") as fake_file:
            result = [line.rstrip() for line in fake_file]
        self.assertEqual(contents, result)

    def test_open_with_wplus(self):
        # set up
        file_path = self.make_path("wplus_file")
        self.create_file(file_path, contents="old contents")
        self.assertTrue(self.os.path.exists(file_path))
        with self.open(file_path, "r", encoding="utf8") as fake_file:
            self.assertEqual("old contents", fake_file.read())
            self.assertEqual("r", fake_file.mode)
        # actual tests
        with self.open(file_path, "w+", encoding="utf8") as fake_file:
            fake_file.write("new contents")
            fake_file.seek(0)
            self.assertTrue("new contents", fake_file.read())
            self.assertEqual("w+", fake_file.mode)

    def test_open_with_wplus_binary(self):
        file_path = self.make_path("wplus_file_b")
        self.create_file(file_path, contents=b"old contents")
        self.assertTrue(self.os.path.exists(file_path))
        with self.open(file_path, "rb") as fake_file:
            self.assertEqual(b"old contents", fake_file.read())
            self.assertEqual("rb", fake_file.mode)
        # actual tests
        with self.open(file_path, "wb+") as fake_file:
            fake_file.write(b"new contents")
            fake_file.seek(0)
            self.assertTrue(b"new contents", fake_file.read())
            self.assertEqual("rb+", fake_file.mode)

    def test_open_with_wplus_truncation(self):
        # set up
        file_path = self.make_path("wplus_file")
        self.create_file(file_path, contents="old contents")
        self.assertTrue(self.os.path.exists(file_path))
        with self.open(file_path, "r", encoding="utf8") as fake_file:
            self.assertEqual("old contents", fake_file.read())
        # actual tests
        with self.open(file_path, "w+", encoding="utf8") as fake_file:
            fake_file.seek(0)
            self.assertEqual("", fake_file.read())
            self.assertEqual("w+", fake_file.mode)

    def test_open_with_append_flag(self):
        contents = [
            "I am he as\n",
            "you are he as\n",
            "you are me and\n",
            "we are all together\n",
        ]
        additional_contents = ["These new lines\n", "like you a lot.\n"]
        file_path = self.make_path("appendfile")
        self.create_file(file_path, contents="".join(contents))
        with self.open(file_path, "a", encoding="utf8") as fake_file:
            with self.assertRaises(io.UnsupportedOperation):
                fake_file.read(0)
            with self.assertRaises(io.UnsupportedOperation):
                fake_file.readline()
            self.assertEqual("a", fake_file.mode)
            expected_len = len("".join(contents))
            expected_len += len(contents) * (len(self.os.linesep) - 1)
            self.assertEqual(expected_len, fake_file.tell())
            fake_file.seek(0)
            self.assertEqual(0, fake_file.tell())
            fake_file.writelines(additional_contents)
        with self.open(file_path, encoding="utf8") as fake_file:
            self.assertEqual(contents + additional_contents, fake_file.readlines())

    def test_open_with_append_flag_binary(self):
        contents = b"Just some boring stuff... "
        additional_contents = b"some excitement added"
        file_path = self.make_path("append-binary")
        self.create_file(file_path, contents=contents)
        with self.open(file_path, "ab") as fake_file:
            with self.assertRaises(io.UnsupportedOperation):
                fake_file.read(0)
            self.assertEqual("ab", fake_file.mode)
            self.assertEqual(len(contents), fake_file.tell())
            fake_file.seek(0)
            self.assertEqual(0, fake_file.tell())
            fake_file.write(additional_contents)
        with self.open(file_path, "rb") as fake_file:
            self.assertEqual(contents + additional_contents, fake_file.read())

    def check_append_with_aplus(self):
        file_path = self.make_path("aplus_file")
        self.create_file(file_path, contents="old contents")
        self.assertTrue(self.os.path.exists(file_path))
        with self.open(file_path, "r", encoding="utf8") as fake_file:
            self.assertEqual("old contents", fake_file.read())

        if self.filesystem:
            # need to recreate FakeFileOpen for OS specific initialization
            self.open = fake_filesystem.FakeFileOpen(
                self.filesystem, delete_on_close=True
            )
        with self.open(file_path, "a+", encoding="utf8") as fake_file:
            self.assertEqual("a+", fake_file.mode)
            self.assertEqual(12, fake_file.tell())
            fake_file.write("new contents")
            self.assertEqual(24, fake_file.tell())
            fake_file.seek(0)
            self.assertEqual("old contentsnew contents", fake_file.read())

    def test_append_with_aplus_mac_os(self):
        self.check_macos_only()
        self.check_append_with_aplus()

    def test_append_with_aplus_linux_windows(self):
        self.check_linux_and_windows()
        self.check_append_with_aplus()

    def test_append_with_aplus_read_with_loop(self):
        # set up
        file_path = self.make_path("aplus_file")
        self.create_file(file_path, contents="old contents")
        self.assertTrue(self.os.path.exists(file_path))
        with self.open(file_path, "r", encoding="utf8") as fake_file:
            self.assertEqual("old contents", fake_file.read())
        # actual tests
        with self.open(file_path, "a+", encoding="utf8") as fake_file:
            fake_file.seek(0)
            fake_file.write("new contents")
            fake_file.seek(0)
            for line in fake_file:
                self.assertEqual("old contentsnew contents", line)

    def test_read_empty_file_with_aplus(self):
        file_path = self.make_path("aplus_file")
        with self.open(file_path, "a+", encoding="utf8") as fake_file:
            self.assertEqual("", fake_file.read())

    def test_read_empty_file_with_aplus_binary(self):
        file_path = self.make_path("aplus_file")
        with self.open(file_path, "ab+") as fake_file:
            self.assertEqual(b"", fake_file.read())
            self.assertEqual("ab+", fake_file.mode)

    def test_read_with_rplus(self):
        # set up
        file_path = self.make_path("rplus_file")
        self.create_file(file_path, contents="old contents here")
        self.assertTrue(self.os.path.exists(file_path))
        with self.open(file_path, "r", encoding="utf8") as fake_file:
            self.assertEqual("old contents here", fake_file.read())
        # actual tests
        with self.open(file_path, "r+", encoding="utf8") as fake_file:
            self.assertEqual("old contents here", fake_file.read())
            self.assertEqual("r+", fake_file.mode)
            fake_file.seek(0)
            fake_file.write("new contents")
            fake_file.seek(0)
            self.assertEqual("new contents here", fake_file.read())

    def test_read_with_rplus_binary(self):
        file_path = self.make_path("rplus_binary")
        self.create_file(file_path, contents=b"old contents here")
        self.assertTrue(self.os.path.exists(file_path))
        with self.open(file_path, "rb") as fake_file:
            self.assertEqual(b"old contents here", fake_file.read())

        with self.open(file_path, "rb+") as fake_file:
            self.assertEqual(b"old contents here", fake_file.read())
            self.assertEqual("rb+", fake_file.mode)
            fake_file.seek(0)
            fake_file.write(b"new contents")
            fake_file.seek(0)
            self.assertEqual(b"new contents here", fake_file.read())

    def create_with_permission(self, file_path, perm_bits):
        self.create_file(file_path)
        self.os.chmod(file_path, perm_bits)
        if perm_bits & helpers.PERM_READ:
            st = self.os.stat(file_path)
            self.assert_mode_equal(perm_bits, st.st_mode)
            self.assertTrue(st.st_mode & stat.S_IFREG)
            self.assertFalse(st.st_mode & stat.S_IFDIR)

    def test_open_flags700(self):
        # set up
        self.check_posix_only()
        file_path = self.make_path("target_file")
        self.create_with_permission(file_path, 0o700)
        # actual tests
        self.open(file_path, "r", encoding="utf8").close()
        self.open(file_path, "w", encoding="utf8").close()
        self.open(file_path, "w+", encoding="utf8").close()
        with self.assertRaises(ValueError):
            self.open(file_path, "INV", encoding="utf8")

    def test_open_flags400(self):
        # set up
        self.check_posix_only()
        file_path = self.make_path("target_file")
        self.create_with_permission(file_path, 0o400)
        # actual tests
        self.open(file_path, "r", encoding="utf8").close()
        if not is_root():
            self.assert_raises_os_error(errno.EACCES, self.open, file_path, "w")
            self.assert_raises_os_error(errno.EACCES, self.open, file_path, "w+")
        else:
            self.open(file_path, "w", encoding="utf8").close()
            self.open(file_path, "w+", encoding="utf8").close()

    def test_open_flags200(self):
        # set up
        self.check_posix_only()
        file_path = self.make_path("target_file")
        self.create_with_permission(file_path, 0o200)
        # actual tests
        self.open(file_path, "w", encoding="utf8").close()
        if not is_root():
            with self.assertRaises(OSError):
                self.open(file_path, "r", encoding="utf8")
            with self.assertRaises(OSError):
                self.open(file_path, "w+", encoding="utf8")
        else:
            self.open(file_path, "r", encoding="utf8").close()
            self.open(file_path, "w+", encoding="utf8").close()

    def test_open_flags100(self):
        # set up
        self.check_posix_only()
        file_path = self.make_path("target_file")
        self.create_with_permission(file_path, 0o100)
        # actual tests
        if not is_root():
            with self.assertRaises(OSError):
                self.open(file_path, "r", encoding="utf8")
            with self.assertRaises(OSError):
                self.open(file_path, "w", encoding="utf8")
            with self.assertRaises(OSError):
                self.open(file_path, "w+", encoding="utf8")
        else:
            self.open(file_path, "r", encoding="utf8").close()
            self.open(file_path, "w", encoding="utf8").close()
            self.open(file_path, "w+", encoding="utf8").close()

    def test_follow_link_read(self):
        skip_if_symlink_not_supported()
        link_path = self.make_path("foo", "bar", "baz")
        target = self.make_path("tarJAY")
        target_contents = "real baz contents"
        self.create_file(target, contents=target_contents)
        self.create_symlink(link_path, target)
        self.assert_equal_paths(target, self.os.readlink(link_path))
        fh = self.open(link_path, "r", encoding="utf8")
        got_contents = fh.read()
        fh.close()
        self.assertEqual(target_contents, got_contents)

    def test_follow_link_write(self):
        skip_if_symlink_not_supported()
        link_path = self.make_path("foo", "bar", "TBD")
        target = self.make_path("tarJAY")
        target_contents = "real baz contents"
        self.create_symlink(link_path, target)
        self.assertFalse(self.os.path.exists(target))

        with self.open(link_path, "w", encoding="utf8") as fh:
            fh.write(target_contents)
        with self.open(target, "r", encoding="utf8") as fh:
            got_contents = fh.read()
        self.assertEqual(target_contents, got_contents)

    def test_follow_intra_path_link_write(self):
        # Test a link in the middle of of a file path.
        skip_if_symlink_not_supported()
        link_path = self.os.path.join(
            self.base_path, "foo", "build", "local_machine", "output", "1"
        )
        target = self.make_path("tmp", "output", "1")
        self.create_dir(self.make_path("tmp", "output"))
        self.create_symlink(
            self.os.path.join(self.base_path, "foo", "build", "local_machine"),
            self.make_path("tmp"),
        )

        self.assertFalse(self.os.path.exists(link_path))
        self.assertFalse(self.os.path.exists(target))

        target_contents = "real baz contents"
        with self.open(link_path, "w", encoding="utf8") as fh:
            fh.write(target_contents)
        with self.open(target, "r", encoding="utf8") as fh:
            got_contents = fh.read()
        self.assertEqual(target_contents, got_contents)

    def test_open_raises_on_symlink_loop(self):
        # Regression test for #274
        self.check_posix_only()
        file_dir = self.make_path("foo")
        self.os.mkdir(file_dir)
        file_path = self.os.path.join(file_dir, "baz")
        self.os.symlink(file_path, file_path)
        self.assert_raises_os_error(errno.ELOOP, self.open, file_path)

    def test_file_descriptors_for_different_files(self):
        first_path = self.make_path("some_file1")
        self.create_file(first_path, contents="contents here1")
        second_path = self.make_path("some_file2")
        self.create_file(second_path, contents="contents here2")
        third_path = self.make_path("some_file3")
        self.create_file(third_path, contents="contents here3")

        with self.open(first_path, encoding="utf8") as fake_file1:
            with self.open(second_path, encoding="utf8") as fake_file2:
                with self.open(third_path, encoding="utf8") as fake_file3:
                    fileno2 = fake_file2.fileno()
                    self.assertGreater(fileno2, fake_file1.fileno())
                    self.assertGreater(fake_file3.fileno(), fileno2)

    def test_file_descriptors_for_the_same_file_are_different(self):
        first_path = self.make_path("some_file1")
        self.create_file(first_path, contents="contents here1")
        second_path = self.make_path("some_file2")
        self.create_file(second_path, contents="contents here2")
        with self.open(first_path, encoding="utf8") as fake_file1:
            with self.open(second_path, encoding="utf8") as fake_file2:
                with self.open(first_path, encoding="utf8") as fake_file1a:
                    fileno2 = fake_file2.fileno()
                    self.assertNotEqual(fileno2, fake_file1.fileno())
                    self.assertNotEqual(fake_file1a.fileno(), fileno2)

    def test_reused_file_descriptors_do_not_affect_others(self):
        first_path = self.make_path("some_file1")
        self.create_file(first_path, contents="contents here1")
        second_path = self.make_path("some_file2")
        self.create_file(second_path, contents="contents here2")
        third_path = self.make_path("some_file3")
        self.create_file(third_path, contents="contents here3")

        with self.open(first_path, "r", encoding="utf8") as fake_file1:
            with self.open(second_path, "r", encoding="utf8") as fake_file2:
                fake_file3 = self.open(third_path, "r", encoding="utf8")
                fake_file1a = self.open(first_path, "r", encoding="utf8")
                fileno1 = fake_file1.fileno()
                fileno2 = fake_file2.fileno()
                fileno3 = fake_file3.fileno()
                fileno4 = fake_file1a.fileno()

        with self.open(second_path, "r", encoding="utf8") as fake_file2:
            with self.open(first_path, "r", encoding="utf8") as fake_file1b:
                self.assertEqual(fileno1, fake_file2.fileno())
                self.assertEqual(fileno2, fake_file1b.fileno())
                self.assertEqual(fileno3, fake_file3.fileno())
                self.assertEqual(fileno4, fake_file1a.fileno())
        fake_file3.close()
        fake_file1a.close()

    def test_intertwined_read_write(self):
        file_path = self.make_path("some_file")
        self.create_file(file_path)

        with self.open(file_path, "a", encoding="utf8") as writer:
            with self.open(file_path, "r", encoding="utf8") as reader:
                writes = [
                    "hello",
                    "world\n",
                    "somewhere\nover",
                    "the\n",
                    "rainbow",
                ]
                reads = []
                # when writes are flushes, they are piped to the reader
                for write in writes:
                    writer.write(write)
                    writer.flush()
                    reads.append(reader.read())
                    reader.flush()
                self.assertEqual(writes, reads)
                writes = ["nothing", "to\nsee", "here"]
                reads = []
                # when writes are not flushed, the reader doesn't read
                # anything new
                for write in writes:
                    writer.write(write)
                    reads.append(reader.read())
                self.assertEqual(["" for _ in writes], reads)

    def test_intertwined_read_write_python3_str(self):
        file_path = self.make_path("some_file")
        self.create_file(file_path)

        with self.open(file_path, "a", encoding="utf-8") as writer:
            with self.open(file_path, "r", encoding="utf-8") as reader:
                writes = ["привет", "мир\n", "где-то\nза", "радугой"]
                reads = []
                # when writes are flushes, they are piped to the reader
                for write in writes:
                    writer.write(write)
                    writer.flush()
                    reads.append(reader.read())
                    reader.flush()
                self.assertEqual(writes, reads)
                writes = ["ничего", "не\nвидно"]
                reads = []
                # when writes are not flushed, the reader doesn't
                # read anything new
                for write in writes:
                    writer.write(write)
                    reads.append(reader.read())
                self.assertEqual(["" for _ in writes], reads)

    def test_open_io_errors(self):
        file_path = self.make_path("some_file")
        self.create_file(file_path)

        with self.open(file_path, "a", encoding="utf8") as fh:
            with self.assertRaises(OSError):
                fh.read()
            with self.assertRaises(OSError):
                fh.readlines()
        with self.open(file_path, "w", encoding="utf8") as fh:
            with self.assertRaises(OSError):
                fh.read()
            with self.assertRaises(OSError):
                fh.readlines()
        with self.open(file_path, "r", encoding="utf8") as fh:
            with self.assertRaises(OSError):
                fh.truncate()
            with self.assertRaises(OSError):
                fh.write("contents")
            with self.assertRaises(OSError):
                fh.writelines(["con", "tents"])

        def _iterator_open(mode):
            with self.open(file_path, mode, encoding="utf8") as f:
                for _ in f:
                    pass

        with self.assertRaises(OSError):
            _iterator_open("w")
        with self.assertRaises(OSError):
            _iterator_open("a")

    def test_open_raises_io_error_if_parent_is_file_posix(self):
        self.check_posix_only()
        file_path = self.make_path("bar")
        self.create_file(file_path)
        file_path = self.os.path.join(file_path, "baz")
        self.assert_raises_os_error(errno.ENOTDIR, self.open, file_path, "w")

    def test_open_raises_io_error_if_parent_is_file_windows(self):
        self.check_windows_only()
        file_path = self.make_path("bar")
        self.create_file(file_path)
        file_path = self.os.path.join(file_path, "baz")
        self.assert_raises_os_error(errno.ENOENT, self.open, file_path, "w")

    def check_open_with_trailing_sep(self, error_nr):
        # regression test for #362
        path = self.make_path("foo") + self.os.path.sep
        self.assert_raises_os_error(error_nr, self.open, path, "w")

    def test_open_with_trailing_sep_linux(self):
        self.check_linux_only()
        self.check_open_with_trailing_sep(errno.EISDIR)

    def test_open_with_trailing_sep_macos(self):
        self.check_macos_only()
        self.check_open_with_trailing_sep(errno.ENOENT)

    def test_open_with_trailing_sep_windows(self):
        self.check_windows_only()
        self.check_open_with_trailing_sep(errno.EINVAL)

    def test_can_read_from_block_device(self):
        self.skip_real_fs()
        device_path = "device"
        self.filesystem.create_file(device_path, stat.S_IFBLK | helpers.PERM_ALL)
        with self.open(device_path, "r", encoding="utf8") as fh:
            self.assertEqual("", fh.read())

    def test_truncate_flushes_contents(self):
        # Regression test for #285
        file_path = self.make_path("baz")
        self.create_file(file_path)
        with self.open(file_path, "w", encoding="utf8") as f0:
            f0.write("test")
            f0.truncate()
            self.assertEqual(4, self.os.path.getsize(file_path))

    def test_update_other_instances_of_same_file_on_flush(self):
        # Regression test for #302
        file_path = self.make_path("baz")
        with self.open(file_path, "w", encoding="utf8") as f0:
            with self.open(file_path, "w", encoding="utf8") as f1:
                f0.write("test")
                f0.truncate()
                f1.flush()
                self.assertEqual(4, self.os.path.getsize(file_path))

    def test_getsize_after_truncate(self):
        # Regression test for #412
        file_path = self.make_path("foo")
        with self.open(file_path, "a", encoding="utf8") as f:
            f.write("a")
            f.seek(0)
            f.truncate()
            f.write("b")
            f.truncate()
            self.assertEqual(1, self.os.path.getsize(file_path))
            self.assertEqual(1, self.os.stat(file_path).st_size)

    def test_st_size_after_truncate(self):
        # Regression test for #412
        file_path = self.make_path("foo")
        with self.open(file_path, "a", encoding="utf8") as f:
            f.write("a")
            f.truncate()
            f.write("b")
            f.truncate()
            self.assertEqual(2, self.os.stat(file_path).st_size)

    def test_that_read_over_end_does_not_reset_position(self):
        # Regression test for #286
        file_path = self.make_path("baz")
        self.create_file(file_path)
        with self.open(file_path, encoding="utf8") as f0:
            f0.seek(2)
            f0.read()
            self.assertEqual(2, f0.tell())

    def test_accessing_closed_file_raises(self):
        # Regression test for #275, #280
        if self.is_pypy:
            raise unittest.SkipTest("Different exceptions with PyPy")
        file_path = self.make_path("foo")
        self.create_file(file_path, contents=b"test")
        fake_file = self.open(file_path, "r", encoding="utf8")
        fake_file.close()
        with self.assertRaises(ValueError):
            fake_file.read(1)
        with self.assertRaises(ValueError):
            fake_file.write("a")
        with self.assertRaises(ValueError):
            fake_file.readline()
        with self.assertRaises(ValueError):
            fake_file.truncate()
        with self.assertRaises(ValueError):
            fake_file.tell()
        with self.assertRaises(ValueError):
            fake_file.seek(1)
        with self.assertRaises(ValueError):
            fake_file.flush()

    def test_accessing_open_file_with_another_handle_raises(self):
        # Regression test for #282
        if self.is_pypy:
            raise unittest.SkipTest("Different exceptions with PyPy")
        file_path = self.make_path("foo")
        f0 = self.os.open(file_path, os.O_CREAT | os.O_WRONLY | os.O_TRUNC)
        fake_file = self.open(file_path, "r", encoding="utf8")
        fake_file.close()
        with self.assertRaises(ValueError):
            fake_file.read(1)
        with self.assertRaises(ValueError):
            fake_file.write("a")
        self.os.close(f0)

    def test_tell_flushes_under_mac_os(self):
        # Regression test for #288
        self.check_macos_only()
        file_path = self.make_path("foo")
        with self.open(file_path, "w", encoding="utf8") as f0:
            f0.write("test")
            self.assertEqual(4, f0.tell())
            self.assertEqual(4, self.os.path.getsize(file_path))

    def test_tell_flushes_in_python3(self):
        # Regression test for #288
        self.check_linux_and_windows()
        file_path = self.make_path("foo")
        with self.open(file_path, "w", encoding="utf8") as f0:
            f0.write("test")
            self.assertEqual(4, f0.tell())
            self.assertEqual(4, self.os.path.getsize(file_path))

    def test_read_flushes_under_posix(self):
        # Regression test for #278
        self.check_posix_only()
        file_path = self.make_path("foo")
        with self.open(file_path, "a+", encoding="utf8") as f0:
            f0.write("test")
            self.assertEqual("", f0.read())
            self.assertEqual(4, self.os.path.getsize(file_path))

    def test_read_flushes_under_windows_in_python3(self):
        # Regression test for #278
        self.check_windows_only()
        file_path = self.make_path("foo")
        with self.open(file_path, "w+", encoding="utf8") as f0:
            f0.write("test")
            f0.read()
            self.assertEqual(4, self.os.path.getsize(file_path))

    def test_seek_flushes(self):
        # Regression test for #290
        file_path = self.make_path("foo")
        with self.open(file_path, "w", encoding="utf8") as f0:
            f0.write("test")
            self.assertEqual(0, self.os.path.getsize(file_path))
            f0.seek(3)
            self.assertEqual(4, self.os.path.getsize(file_path))

    def test_truncate_flushes(self):
        # Regression test for #291
        file_path = self.make_path("foo")
        with self.open(file_path, "a", encoding="utf8") as f0:
            f0.write("test")
            self.assertEqual(0, self.os.path.getsize(file_path))
            f0.truncate()
            self.assertEqual(4, self.os.path.getsize(file_path))

    def check_seek_outside_and_truncate_sets_size(self, mode):
        # Regression test for #294 and #296
        file_path = self.make_path("baz")
        with self.open(file_path, mode, encoding="utf8") as f0:
            f0.seek(1)
            f0.truncate()
            self.assertEqual(1, f0.tell())
            self.assertEqual(1, self.os.path.getsize(file_path))
            f0.seek(1)
            self.assertEqual(1, self.os.path.getsize(file_path))
        self.assertEqual(1, self.os.path.getsize(file_path))

    def test_seek_outside_and_truncate_sets_size_in_write_mode(self):
        # Regression test for #294
        self.check_seek_outside_and_truncate_sets_size("w")

    def test_seek_outside_and_truncate_sets_size_in_append_mode(self):
        # Regression test for #295
        self.check_seek_outside_and_truncate_sets_size("a")

    def test_closed(self):
        file_path = self.make_path("foo")
        f = self.open(file_path, "w", encoding="utf8")
        self.assertFalse(f.closed)
        f.close()
        self.assertTrue(f.closed)
        f = self.open(file_path, encoding="utf8")
        self.assertFalse(f.closed)
        f.close()
        self.assertTrue(f.closed)

    def test_closing_closed_file_does_nothing(self):
        # Regression test for #299
        file_path = self.make_path("baz")
        f0 = self.open(file_path, "w", encoding="utf8")
        f0.close()
        with self.open(file_path, encoding="utf8") as f1:
            # would close f1 if not handled
            f0.close()
            self.assertEqual("", f1.read())

    def test_closing_file_with_different_close_mode(self):
        self.skip_real_fs()
        filename = self.make_path("test.txt")
        fd = self.os.open(filename, os.O_CREAT | os.O_RDWR)
        file_obj = self.filesystem.get_object(filename)
        with self.open(fd, "wb", closefd=False) as fp:
            fp.write(b"test")
            self.assertEqual("wb", fp.mode)
        self.assertTrue(self.filesystem.has_open_file(file_obj))
        self.os.close(fd)
        self.assertFalse(self.filesystem.has_open_file(file_obj))

    def test_truncate_flushes_zeros(self):
        # Regression test for #301
        file_path = self.make_path("baz")
        with self.open(file_path, "w", encoding="utf8") as f0:
            with self.open(file_path, encoding="utf8") as f1:
                f0.seek(1)
                f0.truncate()
                self.assertEqual("\0", f1.read())

    def test_byte_filename(self):
        file_path = self.make_path(b"test")
        with self.open(file_path, "wb") as f:
            f.write(b"test")
        with self.open(file_path, "rb") as f:
            self.assertEqual(b"test", f.read())

    def test_unicode_filename(self):
        file_path = self.make_path("тест")
        with self.open(file_path, "wb") as f:
            f.write(b"test")
        with self.open(file_path, "rb") as f:
            self.assertEqual(b"test", f.read())

    def test_write_devnull(self):
        for mode in ("r+", "w", "w+", "a", "a+"):
            with self.open(self.os.devnull, mode, encoding="utf8") as f:
                f.write("test")
            with self.open(self.os.devnull, encoding="utf8") as f:
                self.assertEqual("", f.read())

    def test_utf16_text(self):
        # regression test for #574
        file_path = self.make_path("foo")
        with self.open(file_path, "w", encoding="utf-16") as f:
            assert f.write("1") == 1

        with self.open(file_path, "a", encoding="utf-16") as f:
            assert f.write("2") == 1

        with self.open(file_path, "r", encoding="utf-16") as f:
            text = f.read()
            assert text == "12"


class RealFileOpenTest(FakeFileOpenTest):
    def use_real_fs(self):
        return True


class FakeFileOpenWithOpenerTest(FakeFileOpenTestBase):
    def opener(self, path, flags):
        return self.os.open(path, flags)

    def test_use_opener_with_read(self):
        file_path = self.make_path("foo")
        self.create_file(file_path, contents="test")
        with self.open(file_path, encoding="utf8", opener=self.opener) as f:
            assert f.read() == "test"
            with self.assertRaises(OSError):
                f.write("foo")

    def test_no_opener_with_read(self):
        file_path = self.make_path("foo")
        self.create_file(file_path, contents="test")
        with self.open(file_path, encoding="utf8") as f:
            assert f.read() == "test"
            with self.assertRaises(OSError):
                f.write("foo")

    def test_use_opener_with_read_plus(self):
        file_path = self.make_path("foo")
        self.create_file(file_path, contents="test")
        with self.open(file_path, "r+", encoding="utf8", opener=self.opener) as f:
            assert f.read() == "test"
            assert f.write("bar") == 3
        with self.open(file_path, encoding="utf8") as f:
            assert f.read() == "testbar"

    def test_use_opener_with_write(self):
        file_path = self.make_path("foo")
        self.create_file(file_path, contents="foo")
        with self.open(file_path, "w", encoding="utf8", opener=self.opener) as f:
            with self.assertRaises(OSError):
                f.read()
            assert f.write("bar") == 3
        with self.open(file_path, encoding="utf8") as f:
            assert f.read() == "bar"

    def test_use_opener_with_write_plus(self):
        file_path = self.make_path("foo")
        self.create_file(file_path, contents="test")
        with self.open(file_path, "w+", encoding="utf8", opener=self.opener) as f:
            assert f.read() == ""
            assert f.write("bar") == 3
        with self.open(file_path, encoding="utf8") as f:
            assert f.read() == "bar"

    def test_use_opener_with_append(self):
        file_path = self.make_path("foo")
        self.create_file(file_path, contents="foo")
        with self.open(file_path, "a", encoding="utf8", opener=self.opener) as f:
            assert f.write("bar") == 3
            with self.assertRaises(OSError):
                f.read()
        with self.open(file_path, encoding="utf8") as f:
            assert f.read() == "foobar"

    def test_use_opener_with_append_plus(self):
        file_path = self.make_path("foo")
        self.create_file(file_path, contents="foo")
        with self.open(file_path, "a+", encoding="utf8", opener=self.opener) as f:
            assert f.read() == ""
            assert f.write("bar") == 3
        with self.open(file_path, encoding="utf8") as f:
            assert f.read() == "foobar"

    def test_use_opener_with_exclusive_write(self):
        file_path = self.make_path("foo")
        self.create_file(file_path, contents="test")
        with self.assertRaises(OSError):
            self.open(file_path, "x", encoding="utf8", opener=self.opener)

        file_path = self.make_path("bar")
        with self.open(file_path, "x", encoding="utf8", opener=self.opener) as f:
            self.assertEqual("x", f.mode)
            assert f.write("bar") == 3
            with self.assertRaises(OSError):
                f.read()
        with self.open(file_path, encoding="utf8") as f:
            assert f.read() == "bar"

    def test_use_opener_with_exclusive_plus(self):
        file_path = self.make_path("foo")
        self.create_file(file_path, contents="test")
        with self.assertRaises(OSError):
            self.open(file_path, "x+", encoding="utf8", opener=self.opener)

        file_path = self.make_path("bar")
        with self.open(file_path, "x+", encoding="utf8", opener=self.opener) as f:
            self.assertEqual("x+", f.mode)
            assert f.write("bar") == 3
            assert f.read() == ""
        with self.open(file_path, encoding="utf8") as f:
            assert f.read() == "bar"


class RealFileOpenWithOpenerTest(FakeFileOpenWithOpenerTest):
    def use_real_fs(self):
        return True


@unittest.skipIf(sys.version_info < (3, 8), "open_code only present since Python 3.8")
class FakeFilePatchedOpenCodeTest(FakeFileOpenTestBase):
    def setUp(self):
        super().setUp()
        if self.use_real_fs():
            self.open_code = io.open_code
        else:
            self.filesystem.patch_open_code = PatchMode.ON
            self.open_code = self.fake_io_module.open_code

    def tearDown(self):
        if not self.use_real_fs():
            self.filesystem.patch_open_code = False
        super().tearDown()

    @unittest.skipIf(IS_PYPY, "Different behavior in PyPy")
    def test_invalid_path(self):
        with self.assertRaises(TypeError):
            self.open_code(4)

    @unittest.skipIf(not IS_PYPY, "Different behavior in PyPy")
    def test_open_code_fd_pypy(self):
        file_path = self.make_path("foo")
        self.create_file(file_path, contents="test")
        fd = self.os.open(file_path, os.O_RDONLY)
        with self.open_code(fd) as f:
            assert f.read() == b"test"

    def test_byte_contents_open_code(self):
        byte_fractions = b"\xe2\x85\x93 \xe2\x85\x94 \xe2\x85\x95 \xe2\x85\x96"
        file_path = self.make_path("foo")
        self.create_file(file_path, contents=byte_fractions)
        with self.open_code(file_path) as f:
            contents = f.read()
        self.assertEqual(contents, byte_fractions)

    def test_open_code_in_real_fs(self):
        self.skip_real_fs()
        file_path = __file__
        with self.assertRaises(OSError):
            self.open_code(file_path)


class RealPatchedFileOpenCodeTest(FakeFilePatchedOpenCodeTest):
    def use_real_fs(self):
        return True


@unittest.skipIf(sys.version_info < (3, 8), "open_code only present since Python 3.8")
class FakeFileUnpatchedOpenCodeTest(FakeFileOpenTestBase):
    def setUp(self):
        super().setUp()
        if self.use_real_fs():
            self.open_code = io.open_code
        else:
            self.open_code = self.fake_io_module.open_code

    @unittest.skipIf(IS_PYPY, "Different behavior in PyPy")
    def test_invalid_path(self):
        with self.assertRaises(TypeError):
            self.open_code(4)

    def test_open_code_in_real_fs(self):
        file_path = __file__

        with self.open_code(file_path) as f:
            contents = f.read()
        self.assertTrue(len(contents) > 100)


class RealUnpatchedFileOpenCodeTest(FakeFileUnpatchedOpenCodeTest):
    def use_real_fs(self):
        return True

    def test_byte_contents_open_code(self):
        byte_fractions = b"\xe2\x85\x93 \xe2\x85\x94 \xe2\x85\x95 \xe2\x85\x96"
        file_path = self.make_path("foo")
        self.create_file(file_path, contents=byte_fractions)
        with self.open_code(file_path) as f:
            contents = f.read()
        self.assertEqual(contents, byte_fractions)


class BufferingModeTest(FakeFileOpenTestBase):
    def test_no_buffering(self):
        file_path = self.make_path("buffertest.bin")
        with self.open(file_path, "wb", buffering=0) as f:
            f.write(b"a" * 128)
            with self.open(file_path, "rb") as r:
                x = r.read()
                self.assertEqual(b"a" * 128, x)

    def test_no_buffering_not_allowed_in_textmode(self):
        file_path = self.make_path("buffertest.txt")
        with self.assertRaises(ValueError):
            self.open(file_path, "w", encoding="utf8", buffering=0)

    def test_default_buffering_no_flush(self):
        file_path = self.make_path("buffertest.bin")
        with self.open(file_path, "wb") as f:
            f.write(b"a" * 2048)
            with self.open(file_path, "rb") as r:
                x = r.read()
                self.assertEqual(b"", x)
        with self.open(file_path, "rb") as r:
            x = r.read()
            self.assertEqual(b"a" * 2048, x)

    def test_default_buffering_flush(self):
        file_path = self.make_path("buffertest.bin")
        with self.open(file_path, "wb") as f:
            f.write(b"a" * 2048)
            f.flush()
            with self.open(file_path, "rb") as r:
                x = r.read()
                self.assertEqual(b"a" * 2048, x)

    def test_writing_with_specific_buffer(self):
        file_path = self.make_path("buffertest.bin")
        with self.open(file_path, "wb", buffering=512) as f:
            f.write(b"a" * 500)
            with self.open(file_path, "rb") as r:
                x = r.read()
                # buffer not filled - not written
                self.assertEqual(0, len(x))
            f.write(b"a" * 400)
            with self.open(file_path, "rb") as r:
                x = r.read()
                # buffer exceeded, but new buffer (400) not - previous written
                self.assertEqual(500, len(x))
            f.write(b"a" * 100)
            with self.open(file_path, "rb") as r:
                x = r.read()
                # buffer not full (500) not written
                self.assertEqual(500, len(x))
            f.write(b"a" * 100)
            with self.open(file_path, "rb") as r:
                x = r.read()
                # buffer exceeded (600) -> write previous
                # new buffer not full (100) - not written
                self.assertEqual(1000, len(x))
            f.write(b"a" * 600)
            with self.open(file_path, "rb") as r:
                x = r.read()
                # new buffer exceeded (600) -> all written
                self.assertEqual(1700, len(x))

    def test_writing_text_with_line_buffer(self):
        file_path = self.make_path("buffertest.bin")
        with self.open(file_path, "w", encoding="utf8", buffering=1) as f:
            f.write("test" * 100)
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                # no new line - not written
                self.assertEqual(0, len(x))
            f.write("\ntest")
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                # new line - buffer written
                self.assertEqual(405, len(x))
            f.write("test" * 10)
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                # buffer not filled - not written
                self.assertEqual(405, len(x))
            f.write("\ntest")
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                # new line - buffer written
                self.assertEqual(450, len(x))

    def test_writing_large_text_with_line_buffer(self):
        file_path = self.make_path("buffertest.bin")
        with self.open(file_path, "w", encoding="utf8", buffering=1) as f:
            f.write("test" * 33000)
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                # buffer larger than default - written
                self.assertEqual(132000, len(x))
            f.write("test")
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                # buffer not filled - not written
                self.assertEqual(132000, len(x))
            f.write("\ntest")
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                # new line - buffer written
                self.assertEqual(132009, len(x))
            f.write("\ntest")
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                # another new line - buffer written
                self.assertEqual(132014, len(x))

    def test_writing_text_with_default_buffer(self):
        file_path = self.make_path("buffertest.txt")
        with self.open(file_path, "w", encoding="utf8") as f:
            f.write("test" * 5)
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                # buffer not filled - not written
                self.assertEqual(0, len(x))
            f.write("\ntest")
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                # buffer exceeded, but new buffer (400) not - previous written
                self.assertEqual(0, len(x))
            f.write("test" * 10)
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                # buffer not filled - not written
                self.assertEqual(0, len(x))
            f.write("\ntest")
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                self.assertEqual(0, len(x))

    def test_writing_text_with_specific_buffer(self):
        file_path = self.make_path("buffertest.txt")
        with self.open(file_path, "w", encoding="utf8", buffering=2) as f:
            f.write("a" * 8000)
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                # buffer not filled - not written
                self.assertEqual(0, len(x))
            f.write("test")
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                # buffer exceeded, but new buffer (400) not - previous written
                self.assertEqual(0, len(x))
            f.write("test")
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                # buffer not filled - not written
                self.assertEqual(0, len(x))
            f.write("test")
            with self.open(file_path, "r", encoding="utf8") as r:
                x = r.read()
                self.assertEqual(0, len(x))
        # with self.open(file_path, "r") as r:
        #     x = r.read()
        #     self.assertEqual(35, len(x))

    def test_append_with_specific_buffer(self):
        file_path = self.make_path("buffertest.bin")
        with self.open(file_path, "wb", buffering=512) as f:
            f.write(b"a" * 500)
        with self.open(file_path, "ab", buffering=512) as f:
            f.write(b"a" * 500)
            with self.open(file_path, "rb") as r:
                x = r.read()
                # buffer not filled - not written
                self.assertEqual(500, len(x))
            f.write(b"a" * 400)
            with self.open(file_path, "rb") as r:
                x = r.read()
                # buffer exceeded, but new buffer (400) not - previous written
                self.assertEqual(1000, len(x))
            f.write(b"a" * 100)
            with self.open(file_path, "rb") as r:
                x = r.read()
                # buffer not full (500) not written
                self.assertEqual(1000, len(x))
            f.write(b"a" * 100)
            with self.open(file_path, "rb") as r:
                x = r.read()
                # buffer exceeded (600) -> write previous
                # new buffer not full (100) - not written
                self.assertEqual(1500, len(x))
            f.write(b"a" * 600)
            with self.open(file_path, "rb") as r:
                x = r.read()
                # new buffer exceeded (600) -> all written
                self.assertEqual(2200, len(x))

    def test_failed_flush_does_not_truncate_file(self):
        # regression test for #548
        self.skip_real_fs()  # cannot set fs size in real fs
        self.filesystem.set_disk_usage(100)
        self.os.makedirs("foo")
        file_path = self.os.path.join("foo", "bar.txt")
        with self.open(file_path, "wb") as f:
            f.write(b"a" * 50)
            f.flush()
            with self.open(file_path, "rb") as r:
                x = r.read()
                self.assertTrue(x.startswith(b"a" * 50))
            with self.assertRaises(OSError):
                f.write(b"b" * 200)
                f.flush()
            with self.open(file_path, "rb") as r:
                x = r.read()
                self.assertTrue(x.startswith(b"a" * 50))
            f.truncate(50)

    def test_failed_write_does_not_truncate_file(self):
        # test the same with no buffering and no flush
        self.skip_real_fs()  # cannot set fs size in real fs
        self.filesystem.set_disk_usage(100)
        self.os.makedirs("foo")
        file_path = self.os.path.join("foo", "bar.txt")
        with self.open(file_path, "wb", buffering=0) as f:
            f.write(b"a" * 50)
            with self.open(file_path, "rb") as r:
                x = r.read()
                self.assertEqual(b"a" * 50, x)
            with self.assertRaises(OSError):
                f.write(b"b" * 200)
            with self.open(file_path, "rb") as r:
                x = r.read()
                self.assertEqual(b"a" * 50, x)

    def test_writing_over_buffer_end(self):
        # regression test for #1120
        dir_path = self.make_path("foo")
        self.create_dir(dir_path)
        file_path = self.os.path.join(dir_path, "bar.txt")
        line_end_size = len(self.os.linesep)
        char_count = io.DEFAULT_BUFFER_SIZE // 256 - line_end_size
        for line_count in (255, 256, 257, 511, 512, 513):
            with self.open(file_path, "w", encoding="utf8") as f:
                for i in range(line_count):
                    f.write("x" * char_count + "\n")

            with self.open(file_path, encoding="utf8") as f:
                lines = f.readlines()
                self.assertEqual(line_count, len(lines))


class RealBufferingTest(BufferingModeTest):
    def use_real_fs(self):
        return True


class OpenFileWithEncodingTest(FakeFileOpenTestBase):
    """Tests that are similar to some open file tests above but using
    an explicit text encoding."""

    def setUp(self):
        super().setUp()
        self.file_path = self.make_path("foo")

    def test_write_str_read_bytes(self):
        str_contents = "علي بابا"
        with self.open(self.file_path, "w", encoding="arabic") as f:
            f.write(str_contents)
        with self.open(self.file_path, "rb") as f:
            contents = f.read()
        self.assertEqual(str_contents, contents.decode("arabic"))

    def test_write_str_error_modes(self):
        str_contents = "علي بابا"
        with self.open(self.file_path, "w", encoding="cyrillic") as f:
            with self.assertRaises(UnicodeEncodeError):
                f.write(str_contents)

        with self.open(
            self.file_path, "w", encoding="ascii", errors="xmlcharrefreplace"
        ) as f:
            f.write(str_contents)
        with self.open(self.file_path, "r", encoding="ascii") as f:
            contents = f.read()
        self.assertEqual("&#1593;&#1604;&#1610; &#1576;&#1575;&#1576;&#1575;", contents)

        with self.open(
            self.file_path, "w", encoding="ascii", errors="namereplace"
        ) as f:
            f.write(str_contents)
        with self.open(self.file_path, "r", encoding="ascii") as f:
            contents = f.read()
        self.assertEqual(
            r"\N{ARABIC LETTER AIN}\N{ARABIC LETTER LAM}\N"
            r"{ARABIC LETTER YEH} \N{ARABIC LETTER BEH}\N"
            r"{ARABIC LETTER ALEF}\N{ARABIC LETTER BEH}"
            r"\N{ARABIC LETTER ALEF}",
            contents,
        )

    def test_read_str_error_modes(self):
        str_contents = "علي بابا"
        with self.open(self.file_path, "w", encoding="arabic") as f:
            f.write(str_contents)

        # default strict encoding
        with self.open(self.file_path, encoding="ascii") as f:
            with self.assertRaises(UnicodeDecodeError):
                f.read()
        with self.open(self.file_path, encoding="ascii", errors="replace") as f:
            contents = f.read()
        self.assertNotEqual(str_contents, contents)

        with self.open(
            self.file_path, encoding="ascii", errors="backslashreplace"
        ) as f:
            contents = f.read()
        self.assertEqual(r"\xd9\xe4\xea \xc8\xc7\xc8\xc7", contents)

    def test_write_and_read_str(self):
        str_contents = "علي بابا"
        with self.open(self.file_path, "w", encoding="arabic") as f:
            f.write(str_contents)
        with self.open(self.file_path, "r", encoding="arabic") as f:
            contents = f.read()
        self.assertEqual(str_contents, contents)

    def test_create_file_with_append(self):
        contents = [
            "Allons enfants de la Patrie,Le jour de gloire est arrivé!",
            "Contre nous de la tyrannie,",
            "L’étendard sanglant est levé.",
        ]
        with self.open(self.file_path, "a", encoding="utf-8") as fake_file:
            for line in contents:
                fake_file.write(line + "\n")
        with self.open(self.file_path, encoding="utf-8") as fake_file:
            result = [line.rstrip() for line in fake_file]
        self.assertEqual(contents, result)

    def test_append_existing_file(self):
        contents = [
            "Оригинальное содержаниеДополнительное содержание",
        ]
        self.create_file(self.file_path, contents=contents[0], encoding="cyrillic")
        with self.open(self.file_path, "a", encoding="cyrillic") as fake_file:
            for line in contents[1:]:
                fake_file.write(line + "\n")
        with self.open(self.file_path, encoding="cyrillic") as fake_file:
            result = [line.rstrip() for line in fake_file]
        self.assertEqual(contents, result)

    def test_open_with_wplus(self):
        self.create_file(
            self.file_path, contents="старое содержание", encoding="cyrillic"
        )
        with self.open(self.file_path, "r", encoding="cyrillic") as fake_file:
            self.assertEqual("старое содержание", fake_file.read())

        with self.open(self.file_path, "w+", encoding="cyrillic") as fake_file:
            fake_file.write("новое содержание")
            fake_file.seek(0)
            self.assertTrue("новое содержание", fake_file.read())

    def test_open_with_append_flag(self):
        contents = ["Калинка,\n", "калинка,\n", "калинка моя,\n"]
        additional_contents = ["В саду ягода-малинка,\n", "малинка моя.\n"]
        self.create_file(
            self.file_path, contents="".join(contents), encoding="cyrillic"
        )
        with self.open(self.file_path, "a", encoding="cyrillic") as fake_file:
            with self.assertRaises(io.UnsupportedOperation):
                fake_file.read(0)
            with self.assertRaises(io.UnsupportedOperation):
                fake_file.readline()
            self.assertEqual(len("".join(contents)), fake_file.tell())
            fake_file.seek(0)
            self.assertEqual(0, fake_file.tell())
            fake_file.writelines(additional_contents)
        with self.open(self.file_path, encoding="cyrillic") as fake_file:
            self.assertEqual(contents + additional_contents, fake_file.readlines())

    def test_append_with_aplus(self):
        self.create_file(
            self.file_path, contents="старое содержание", encoding="cyrillic"
        )
        fake_file = self.open(self.file_path, "r", encoding="cyrillic")
        fake_file.close()

        with self.open(self.file_path, "a+", encoding="cyrillic") as fake_file:
            self.assertEqual(17, fake_file.tell())
            fake_file.write("новое содержание")
            self.assertEqual(33, fake_file.tell())
            fake_file.seek(0)
            self.assertEqual("старое содержаниеновое содержание", fake_file.read())

    def test_read_with_rplus(self):
        self.create_file(
            self.file_path,
            contents="старое содержание здесь",
            encoding="cyrillic",
        )
        fake_file = self.open(self.file_path, "r", encoding="cyrillic")
        fake_file.close()

        with self.open(self.file_path, "r+", encoding="cyrillic") as fake_file:
            self.assertEqual("старое содержание здесь", fake_file.read())
            fake_file.seek(0)
            fake_file.write("новое  содержание")
            fake_file.seek(0)
            self.assertEqual("новое  содержание здесь", fake_file.read())


class OpenRealFileWithEncodingTest(OpenFileWithEncodingTest):
    def use_real_fs(self):
        return True


class FakeFileOpenLineEndingTest(FakeFileOpenTestBase):
    def setUp(self):
        super().setUp()

    def test_read_default_newline_mode(self):
        file_path = self.make_path("some_file")
        for contents in (b"1\n2", b"1\r\n2", b"1\r2"):
            self.create_file(file_path, contents=contents)
            with self.open(file_path, mode="r", encoding="utf8") as f:
                self.assertEqual(["1\n", "2"], f.readlines())
            with self.open(file_path, mode="r", encoding="utf8") as f:
                self.assertEqual("1\n2", f.read())
            with self.open(file_path, mode="rb") as f:
                self.assertEqual(contents, f.read())

    def test_write_universal_newline_mode(self):
        file_path = self.make_path("some_file")
        with self.open(file_path, "w", encoding="utf8") as f:
            f.write("1\n2")
        with self.open(file_path, mode="rb") as f:
            self.assertEqual(b"1" + self.os.linesep.encode() + b"2", f.read())

        with self.open(file_path, "w", encoding="utf8") as f:
            f.write("1\r\n2")
        with self.open(file_path, mode="rb") as f:
            self.assertEqual(b"1\r" + self.os.linesep.encode() + b"2", f.read())

    def test_read_with_newline_arg(self):
        file_path = self.make_path("some_file")
        file_contents = b"1\r\n2\n3\r4"
        self.create_file(file_path, contents=file_contents)
        with self.open(file_path, mode="r", encoding="utf8", newline="") as f:
            self.assertEqual("1\r\n2\n3\r4", f.read())
        with self.open(file_path, mode="r", encoding="utf8", newline="\r") as f:
            self.assertEqual("1\r\n2\n3\r4", f.read())
        with self.open(file_path, mode="r", encoding="utf8", newline="\n") as f:
            self.assertEqual("1\r\n2\n3\r4", f.read())
        with self.open(file_path, mode="r", encoding="utf8", newline="\r\n") as f:
            self.assertEqual("1\r\n2\n3\r4", f.read())

    def test_readlines_with_newline_arg(self):
        file_path = self.make_path("some_file")
        file_contents = b"1\r\n2\n3\r4"
        self.create_file(file_path, contents=file_contents)
        with self.open(file_path, mode="r", encoding="utf8", newline="") as f:
            self.assertEqual(["1\r\n", "2\n", "3\r", "4"], f.readlines())
        with self.open(file_path, mode="r", encoding="utf8", newline="\r") as f:
            self.assertEqual(["1\r", "\n2\n3\r", "4"], f.readlines())
        with self.open(file_path, mode="r", encoding="utf8", newline="\n") as f:
            self.assertEqual(["1\r\n", "2\n", "3\r4"], f.readlines())
        with self.open(file_path, mode="r", encoding="utf8", newline="\r\n") as f:
            self.assertEqual(["1\r\n", "2\n3\r4"], f.readlines())

    @unittest.skipIf(sys.version_info >= (3, 10), "U flag no longer supported")
    def test_read_with_ignored_universal_newlines_flag(self):
        file_path = self.make_path("some_file")
        file_contents = b"1\r\n2\n3\r4"
        self.create_file(file_path, contents=file_contents)
        with self.open(file_path, mode="r", encoding="utf8", newline="\r") as f:
            self.assertEqual("1\r\n2\n3\r4", f.read())
        with self.open(file_path, mode="r", encoding="utf8", newline="\r") as f:
            self.assertEqual("1\r\n2\n3\r4", f.read())
        with self.open(file_path, mode="U", encoding="utf8", newline="\r") as f:
            self.assertEqual("1\r\n2\n3\r4", f.read())

    @unittest.skipIf(sys.version_info < (3, 11), "U flag still supported")
    def test_universal_newlines_flag_not_supported(self):
        file_path = self.make_path("some_file")
        file_contents = b"1\r\n2\n3\r4"
        self.create_file(file_path, contents=file_contents)
        with self.assertRaises(ValueError):
            self.open(file_path, mode="U", encoding="utf8", newline="\r")

    def test_write_with_newline_arg(self):
        file_path = self.make_path("some_file")
        with self.open(file_path, "w", encoding="utf8", newline="") as f:
            f.write("1\r\n2\n3\r4")
        with self.open(file_path, mode="rb") as f:
            self.assertEqual(b"1\r\n2\n3\r4", f.read())

        with self.open(file_path, "w", encoding="utf8", newline="\n") as f:
            f.write("1\r\n2\n3\r4")
        with self.open(file_path, mode="rb") as f:
            self.assertEqual(b"1\r\n2\n3\r4", f.read())

        with self.open(file_path, "w", encoding="utf8", newline="\r\n") as f:
            f.write("1\r\n2\n3\r4")
        with self.open(file_path, mode="rb") as f:
            self.assertEqual(b"1\r\r\n2\r\n3\r4", f.read())

        with self.open(file_path, "w", encoding="utf8", newline="\r") as f:
            f.write("1\r\n2\n3\r4")
        with self.open(file_path, mode="rb") as f:
            self.assertEqual(b"1\r\r2\r3\r4", f.read())

    def test_binary_readline(self):
        file_path = self.make_path("some_file")
        file_contents = b"\x80\n\x80\r\x80\r\n\x80"

        def chunk_line():
            px = 0
            while px < len(file_contents):
                ix = file_contents.find(b"\n", px)
                if ix == -1:
                    yield file_contents[px:]
                    return
                yield file_contents[px : ix + 1]
                px = ix + 1

        chunked_contents = list(chunk_line())
        self.create_file(file_path, contents=file_contents)
        with self.open(file_path, mode="rb") as f:
            self.assertEqual(chunked_contents, list(f))


class RealFileOpenLineEndingTest(FakeFileOpenLineEndingTest):
    def use_real_fs(self):
        return True


class FakeFileOpenLineEndingWithEncodingTest(FakeFileOpenTestBase):
    def setUp(self):
        super().setUp()

    def test_read_standard_newline_mode(self):
        file_path = self.make_path("some_file")
        for contents in ("раз\nдва", "раз\r\nдва", "раз\rдва"):
            self.create_file(file_path, contents=contents, encoding="cyrillic")
            with self.open(file_path, mode="r", encoding="cyrillic") as fake_file:
                self.assertEqual(["раз\n", "два"], fake_file.readlines())
            with self.open(file_path, mode="r", encoding="cyrillic") as fake_file:
                self.assertEqual("раз\nдва", fake_file.read())

    def test_write_universal_newline_mode(self):
        file_path = self.make_path("some_file")
        with self.open(file_path, "w", encoding="cyrillic") as f:
            f.write("раз\nдва")
        with self.open(file_path, mode="rb") as f:
            self.assertEqual(
                "раз".encode("cyrillic")
                + self.os.linesep.encode()
                + "два".encode("cyrillic"),
                f.read(),
            )

        with self.open(file_path, "w", encoding="cyrillic") as f:
            f.write("раз\r\nдва")
        with self.open(file_path, mode="rb") as f:
            self.assertEqual(
                "раз\r".encode("cyrillic")
                + self.os.linesep.encode()
                + "два".encode("cyrillic"),
                f.read(),
            )

    def test_read_with_newline_arg(self):
        file_path = self.make_path("some_file")
        file_contents = "раз\r\nдва\nтри\rчетыре"
        self.create_file(file_path, contents=file_contents, encoding="cyrillic")
        with self.open(file_path, mode="r", newline="", encoding="cyrillic") as f:
            self.assertEqual("раз\r\nдва\nтри\rчетыре", f.read())
        with self.open(file_path, mode="r", newline="\r", encoding="cyrillic") as f:
            self.assertEqual("раз\r\nдва\nтри\rчетыре", f.read())
        with self.open(file_path, mode="r", newline="\n", encoding="cyrillic") as f:
            self.assertEqual("раз\r\nдва\nтри\rчетыре", f.read())
        with self.open(file_path, mode="r", newline="\r\n", encoding="cyrillic") as f:
            self.assertEqual("раз\r\nдва\nтри\rчетыре", f.read())

    def test_readlines_with_newline_arg(self):
        file_path = self.make_path("some_file")
        file_contents = "раз\r\nдва\nтри\rчетыре"
        self.create_file(file_path, contents=file_contents, encoding="cyrillic")
        with self.open(file_path, mode="r", newline="", encoding="cyrillic") as f:
            self.assertEqual(["раз\r\n", "два\n", "три\r", "четыре"], f.readlines())
        with self.open(file_path, mode="r", newline="\r", encoding="cyrillic") as f:
            self.assertEqual(["раз\r", "\nдва\nтри\r", "четыре"], f.readlines())
        with self.open(file_path, mode="r", newline="\n", encoding="cyrillic") as f:
            self.assertEqual(["раз\r\n", "два\n", "три\rчетыре"], f.readlines())
        with self.open(file_path, mode="r", newline="\r\n", encoding="cyrillic") as f:
            self.assertEqual(["раз\r\n", "два\nтри\rчетыре"], f.readlines())

    def test_write_with_newline_arg(self):
        file_path = self.make_path("some_file")
        with self.open(file_path, "w", newline="", encoding="cyrillic") as f:
            f.write("раз\r\nдва\nтри\rчетыре")
        with self.open(file_path, mode="rb") as f:
            self.assertEqual("раз\r\nдва\nтри\rчетыре".encode("cyrillic"), f.read())

        with self.open(file_path, "w", newline="\n", encoding="cyrillic") as f:
            f.write("раз\r\nдва\nтри\rчетыре")
        with self.open(file_path, mode="rb") as f:
            self.assertEqual("раз\r\nдва\nтри\rчетыре".encode("cyrillic"), f.read())

        with self.open(file_path, "w", newline="\r\n", encoding="cyrillic") as f:
            f.write("раз\r\nдва\nтри\rчетыре")
        with self.open(file_path, mode="rb") as f:
            self.assertEqual("раз\r\r\nдва\r\nтри\rчетыре".encode("cyrillic"), f.read())

        with self.open(file_path, "w", newline="\r", encoding="cyrillic") as f:
            f.write("раз\r\nдва\nтри\rчетыре")
        with self.open(file_path, mode="rb") as f:
            self.assertEqual("раз\r\rдва\rтри\rчетыре".encode("cyrillic"), f.read())


class RealFileOpenLineEndingWithEncodingTest(FakeFileOpenLineEndingWithEncodingTest):
    def use_real_fs(self):
        return True


class OpenWithFileDescriptorTest(FakeFileOpenTestBase):
    def test_open_with_file_descriptor(self):
        file_path = self.make_path("this", "file")
        self.create_file(file_path)
        fd = self.os.open(file_path, os.O_CREAT)
        self.assertEqual(fd, self.open(fd, "r", encoding="utf8").fileno())

    def test_closefd_with_file_descriptor(self):
        file_path = self.make_path("this", "file")
        self.create_file(file_path)
        fd = self.os.open(file_path, os.O_CREAT)
        fh = self.open(fd, "r", encoding="utf8", closefd=False)
        fh.close()
        self.assertIsNotNone(self.filesystem.open_files[fd])
        fh = self.open(fd, "r", encoding="utf8", closefd=True)
        fh.close()
        self.assertIsNone(self.filesystem.open_files[fd])


class OpenWithRealFileDescriptorTest(FakeFileOpenTestBase):
    def use_real_fs(self):
        return True


class OpenWithFlagsTestBase(FakeFileOpenTestBase):
    def setUp(self):
        super().setUp()
        self.file_path = self.make_path("some_file")
        self.file_contents = None

    def open_file(self, mode):
        kwargs = {"mode": mode}
        if "b" not in mode:
            kwargs["encoding"] = "utf8"
        return self.open(self.file_path, **kwargs)

    def open_file_and_seek(self, mode):
        fake_file = self.open(self.file_path, mode=mode)
        fake_file.seek(0, 2)
        return fake_file

    def write_and_reopen_file(self, fake_file, mode="r", encoding=None):
        fake_file.write(self.file_contents)
        fake_file.close()
        args = {"mode": mode}
        if encoding:
            args["encoding"] = encoding
        return self.open(self.file_path, **args)


class OpenWithBinaryFlagsTest(OpenWithFlagsTestBase):
    def setUp(self):
        super().setUp()
        self.file_contents = b"real binary contents: \x1f\x8b"
        self.create_file(self.file_path, contents=self.file_contents)

    def test_read_binary(self):
        with self.open_file("rb") as fake_file:
            self.assertEqual(self.file_contents, fake_file.read())

    def test_write_binary(self):
        with self.open_file_and_seek("wb") as f:
            self.assertEqual(0, f.tell())
            with self.write_and_reopen_file(f, mode="rb") as f1:
                self.assertEqual(self.file_contents, f1.read())
                # Attempt to reopen the file in text mode
                with self.open_file("wb") as f2:
                    with self.write_and_reopen_file(
                        f2, mode="r", encoding="ascii"
                    ) as f3:
                        with self.assertRaises(UnicodeDecodeError):
                            f3.read()

    def test_write_and_read_binary(self):
        with self.open_file_and_seek("w+b") as f:
            self.assertEqual(0, f.tell())
            with self.write_and_reopen_file(f, mode="rb") as f1:
                self.assertEqual(self.file_contents, f1.read())


class RealOpenWithBinaryFlagsTest(OpenWithBinaryFlagsTest):
    def use_real_fs(self):
        return True


class OpenWithTextModeFlagsTest(OpenWithFlagsTestBase):
    def setUp(self):
        super().setUp()
        self.setUpFileSystem()

    def setUpFileSystem(self):
        self.file_path = self.make_path("some_file")
        self.file_contents = b"two\r\nlines"
        self.original_contents = "two\r\nlines"
        self.converted_contents = "two\nlines"
        self.create_file(self.file_path, contents=self.file_contents)

    def test_read_text(self):
        """Test that text mode flag is ignored"""
        self.check_windows_only()
        with self.open_file("r") as f:
            self.assertEqual(self.converted_contents, f.read())
        with self.open_file("rt") as f:
            self.assertEqual(self.converted_contents, f.read())

    def test_mixed_text_and_binary_flags(self):
        with self.assertRaises(ValueError):
            self.open_file_and_seek("w+bt")


class RealOpenWithTextModeFlagsTest(OpenWithTextModeFlagsTest):
    def use_real_fs(self):
        return True


class OpenWithInvalidFlagsTest(FakeFileOpenTestBase):
    def test_capital_r(self):
        with self.assertRaises(ValueError):
            self.open("some_file", "R")

    def test_capital_w(self):
        with self.assertRaises(ValueError):
            self.open("some_file", "W")

    def test_capital_a(self):
        with self.assertRaises(ValueError):
            self.open("some_file", "A")

    def test_lower_u(self):
        with self.assertRaises(ValueError):
            self.open("some_file", "u")

    def test_lower_rw(self):
        with self.assertRaises(ValueError):
            self.open("some_file", "rw")


class OpenWithInvalidFlagsRealFsTest(OpenWithInvalidFlagsTest):
    def use_real_fs(self):
        return True


class ResolvePathTest(FakeFileOpenTestBase):
    def write_to_file(self, file_name):
        with self.open(file_name, "w", encoding="utf8") as fh:
            fh.write("x")

    def test_none_filepath_raises_type_error(self):
        with self.assertRaises(TypeError):
            self.open(None, "w", encoding="utf8")

    def test_empty_filepath_raises_io_error(self):
        with self.assertRaises(OSError):
            self.open("", "w", encoding="utf8")

    def test_normal_path(self):
        file_path = self.make_path("foo")
        self.write_to_file(file_path)
        self.assertTrue(self.os.path.exists(file_path))

    def test_link_within_same_directory(self):
        skip_if_symlink_not_supported()
        final_target = self.make_path("foo", "baz")
        link_path = self.make_path("foo", "bar")
        self.create_symlink(link_path, "baz")
        self.write_to_file(link_path)
        self.assertTrue(self.os.path.exists(final_target))
        self.assertEqual(1, self.os.stat(final_target)[stat.ST_SIZE])

    def test_link_to_sub_directory(self):
        skip_if_symlink_not_supported()
        final_target = self.make_path("foo", "baz", "bip")
        dir_path = self.make_path("foo", "baz")
        self.create_dir(dir_path)
        link_path = self.make_path("foo", "bar")
        target_path = self.os.path.join("baz", "bip")
        self.create_symlink(link_path, target_path)
        self.write_to_file(link_path)
        self.assertTrue(self.os.path.exists(final_target))
        self.assertEqual(1, self.os.stat(final_target)[stat.ST_SIZE])
        self.assertTrue(self.os.path.exists(dir_path))
        # Make sure that intermediate directory got created.
        self.assertTrue(self.os.stat(dir_path)[stat.ST_MODE] & stat.S_IFDIR)

    def test_link_to_parent_directory(self):
        skip_if_symlink_not_supported()
        final_target = self.make_path("baz", "bip")
        self.create_dir(self.make_path("foo"))
        self.create_dir(self.make_path("baz"))
        link_path = self.make_path("foo", "bar")
        self.create_symlink(link_path, self.os.path.join("..", "baz"))
        self.write_to_file(self.make_path("foo", "bar", "bip"))
        self.assertTrue(self.os.path.exists(final_target))
        self.assertEqual(1, self.os.stat(final_target)[stat.ST_SIZE])
        self.assertTrue(self.os.path.exists(link_path))

    def test_link_to_absolute_path(self):
        skip_if_symlink_not_supported()
        final_target = self.make_path("foo", "baz", "bip")
        self.create_dir(self.make_path("foo", "baz"))
        link_path = self.make_path("foo", "bar")
        self.create_symlink(link_path, final_target)
        self.write_to_file(link_path)
        self.assertTrue(self.os.path.exists(final_target))

    def test_relative_links_work_after_chdir(self):
        skip_if_symlink_not_supported()
        final_target = self.make_path("foo", "baz", "bip")
        self.create_dir(self.make_path("foo", "baz"))
        link_path = self.make_path("foo", "bar")
        self.create_symlink(link_path, self.os.path.join(".", "baz", "bip"))
        if not self.is_windows:
            self.assert_equal_paths(final_target, self.os.path.realpath(link_path))

        self.assertTrue(self.os.path.islink(link_path))
        self.os.chdir(self.make_path("foo"))
        self.assert_equal_paths(self.make_path("foo"), self.os.getcwd())
        self.assertTrue(self.os.path.islink("bar"))
        if not self.is_windows:
            self.assert_equal_paths(final_target, self.os.path.realpath("bar"))

        self.write_to_file(link_path)
        self.assertTrue(self.os.path.exists(final_target))

    def test_absolute_links_work_after_chdir(self):
        skip_if_symlink_not_supported()
        final_target = self.make_path("foo", "baz", "bip")
        self.create_dir(self.make_path("foo", "baz"))
        link_path = self.make_path("foo", "bar")
        self.create_symlink(link_path, final_target)
        if not self.is_windows:
            self.assert_equal_paths(final_target, self.os.path.realpath(link_path))

        self.assertTrue(self.os.path.islink(link_path))
        self.os.chdir(self.make_path("foo"))
        self.assert_equal_paths(self.make_path("foo"), self.os.getcwd())
        self.assertTrue(self.os.path.islink("bar"))
        if not self.is_windows:
            self.assert_equal_paths(final_target, self.os.path.realpath("bar"))

        self.write_to_file(link_path)
        self.assertTrue(self.os.path.exists(final_target))

    def test_chdir_through_relative_link(self):
        self.check_posix_only()
        dir1_path = self.make_path("x", "foo")
        dir2_path = self.make_path("x", "bar")
        self.create_dir(dir1_path)
        self.create_dir(dir2_path)
        link_path = self.make_path("x", "foo", "bar")
        self.create_symlink(link_path, self.os.path.join("..", "bar"))
        self.assert_equal_paths(dir2_path, self.os.path.realpath(link_path))

        self.os.chdir(dir1_path)
        self.assert_equal_paths(dir1_path, self.os.getcwd())
        self.assert_equal_paths(dir2_path, self.os.path.realpath("bar"))

        self.os.chdir("bar")
        self.assert_equal_paths(dir2_path, self.os.getcwd())

    def test_chdir_uses_open_fd_as_path(self):
        self.check_posix_only()
        if self.is_pypy:
            # unclear behavior with PyPi
            self.skip_real_fs()
        self.assert_raises_os_error([errno.ENOTDIR, errno.EBADF], self.os.chdir, 500)
        dir_path = self.make_path("foo", "bar")
        self.create_dir(dir_path)

        path_des = self.os.open(dir_path, os.O_RDONLY)
        self.os.chdir(path_des)
        self.os.close(path_des)
        self.assert_equal_paths(dir_path, self.os.getcwd())

    def test_read_link_to_link(self):
        # Write into the final link target and read back from a file which will
        # point to that.
        skip_if_symlink_not_supported()
        link_path = self.make_path("foo", "bar")
        self.create_symlink(link_path, "link")
        self.create_symlink(self.make_path("foo", "link"), "baz")
        self.write_to_file(self.make_path("foo", "baz"))
        fh = self.open(link_path, "r", encoding="utf8")
        self.assertEqual("x", fh.read())

    def test_write_link_to_link(self):
        skip_if_symlink_not_supported()
        final_target = self.make_path("foo", "baz")
        link_path = self.make_path("foo", "bar")
        self.create_symlink(link_path, "link")
        self.create_symlink(self.make_path("foo", "link"), "baz")
        self.write_to_file(link_path)
        self.assertTrue(self.os.path.exists(final_target))

    def test_multiple_links(self):
        skip_if_symlink_not_supported()
        self.os.makedirs(self.make_path("a", "link1", "c", "link2"))

        self.create_symlink(self.make_path("a", "b"), "link1")

        if not self.is_windows:
            self.assert_equal_paths(
                self.make_path("a", "link1"),
                self.os.path.realpath(self.make_path("a", "b")),
            )
            self.assert_equal_paths(
                self.make_path("a", "link1", "c"),
                self.os.path.realpath(self.make_path("a", "b", "c")),
            )

        link_path = self.make_path("a", "link1", "c", "d")
        self.create_symlink(link_path, "link2")
        self.assertTrue(self.os.path.exists(link_path))
        self.assertTrue(self.os.path.exists(self.make_path("a", "b", "c", "d")))

        final_target = self.make_path("a", "link1", "c", "link2", "e")
        self.assertFalse(self.os.path.exists(final_target))
        self.write_to_file(self.make_path("a", "b", "c", "d", "e"))
        self.assertTrue(self.os.path.exists(final_target))

    def test_utime_link(self):
        """os.utime() and os.stat() via symbolic link (issue #49)"""
        skip_if_symlink_not_supported()
        self.create_dir(self.make_path("foo", "baz"))
        target_path = self.make_path("foo", "baz", "bip")
        self.write_to_file(target_path)
        link_name = self.make_path("foo", "bar")
        self.create_symlink(link_name, target_path)

        self.os.utime(link_name, (1, 2))
        st = self.os.stat(link_name)
        self.assertEqual(1, st.st_atime)
        self.assertEqual(2, st.st_mtime)
        self.os.utime(link_name, (3, 4))
        st = self.os.stat(link_name)
        self.assertEqual(3, st.st_atime)
        self.assertEqual(4, st.st_mtime)

    def test_too_many_links(self):
        self.check_posix_only()
        link_path = self.make_path("a", "loop")
        self.create_symlink(link_path, "loop")
        self.assertFalse(self.os.path.exists(link_path))

    def test_that_drive_letters_are_preserved(self):
        self.check_windows_only()
        self.skip_real_fs()
        self.assertEqual("C:!foo!bar", self.filesystem.resolve_path("C:!foo!!bar"))

    def test_that_unc_paths_are_preserved(self):
        self.check_windows_only()
        self.skip_real_fs()
        self.assertEqual(
            "!!foo!bar!baz", self.filesystem.resolve_path("!!foo!bar!baz!!")
        )


class RealResolvePathTest(ResolvePathTest):
    def use_real_fs(self):
        return True


class SkipOpenTest(unittest.TestCase):
    def test_open_in_skipped_module(self):
        with Patcher(additional_skip_names=["skipped_pathlib"]):
            contents = read_open("skipped_pathlib.py")
            self.assertTrue(contents.startswith("# Licensed under the Apache License"))


if __name__ == "__main__":
    unittest.main()
