xref: /third_party/python/Lib/test/support/__init__.py

"""Supporting definitions for the Python regression tests."""

if __name__ != 'test.support':
    raise ImportError('support must be imported from the test package')

import contextlib
import functools
import os
import re
import stat
import sys
import sysconfig
import time
import types
import unittest
import warnings

from .testresult import get_test_runner


try:
    from _testcapi import unicode_legacy_string
except ImportError:
    unicode_legacy_string = None

__all__ = [
    # globals
    "PIPE_MAX_SIZE", "verbose", "max_memuse", "use_resources", "failfast",
    # exceptions
    "Error", "TestFailed", "TestDidNotRun", "ResourceDenied",
    # io
    "record_original_stdout", "get_original_stdout", "captured_stdout",
    "captured_stdin", "captured_stderr",
    # unittest
    "is_resource_enabled", "requires", "requires_freebsd_version",
    "requires_linux_version", "requires_mac_ver",
    "check_syntax_error",
    "BasicTestRunner", "run_unittest", "run_doctest",
    "requires_gzip", "requires_bz2", "requires_lzma",
    "bigmemtest", "bigaddrspacetest", "cpython_only", "get_attribute",
    "requires_IEEE_754", "requires_zlib",
    "anticipate_failure", "load_package_tests", "detect_api_mismatch",
    "check__all__", "skip_if_buggy_ucrt_strfptime",
    "check_disallow_instantiation",
    # sys
    "is_jython", "is_android", "check_impl_detail", "unix_shell",
    "setswitchinterval",
    # network
    "open_urlresource",
    # processes
    "reap_children",
    # miscellaneous
    "run_with_locale", "swap_item", "findfile",
    "swap_attr", "Matcher", "set_memlimit", "SuppressCrashReport", "sortdict",
    "run_with_tz", "PGO", "missing_compiler_executable",
    "ALWAYS_EQ", "NEVER_EQ", "LARGEST", "SMALLEST",
    "LOOPBACK_TIMEOUT", "INTERNET_TIMEOUT", "SHORT_TIMEOUT", "LONG_TIMEOUT",
    ]


# Timeout in seconds for tests using a network server listening on the network
# local loopback interface like 127.0.0.1.
#
# The timeout is long enough to prevent test failure: it takes into account
# that the client and the server can run in different threads or even different
# processes.
#
# The timeout should be long enough for connect(), recv() and send() methods
# of socket.socket.
LOOPBACK_TIMEOUT = 5.0
if sys.platform == 'win32' and ' 32 bit (ARM)' in sys.version:
    # bpo-37553: test_socket.SendfileUsingSendTest is taking longer than 2
    # seconds on Windows ARM32 buildbot
    LOOPBACK_TIMEOUT = 10
elif sys.platform == 'vxworks':
    LOOPBACK_TIMEOUT = 10

# Timeout in seconds for network requests going to the internet. The timeout is
# short enough to prevent a test to wait for too long if the internet request
# is blocked for whatever reason.
#
# Usually, a timeout using INTERNET_TIMEOUT should not mark a test as failed,
# but skip the test instead: see transient_internet().
INTERNET_TIMEOUT = 60.0

# Timeout in seconds to mark a test as failed if the test takes "too long".
#
# The timeout value depends on the regrtest --timeout command line option.
#
# If a test using SHORT_TIMEOUT starts to fail randomly on slow buildbots, use
# LONG_TIMEOUT instead.
SHORT_TIMEOUT = 30.0

# Timeout in seconds to detect when a test hangs.
#
# It is long enough to reduce the risk of test failure on the slowest Python
# buildbots. It should not be used to mark a test as failed if the test takes
# "too long". The timeout value depends on the regrtest --timeout command line
# option.
LONG_TIMEOUT = 5 * 60.0


class Error(Exception):
    """Base class for regression test exceptions."""

class TestFailed(Error):
    """Test failed."""

class TestFailedWithDetails(TestFailed):
    """Test failed."""
    def __init__(self, msg, errors, failures):
        self.msg = msg
        self.errors = errors
        self.failures = failures
        super().__init__(msg, errors, failures)

    def __str__(self):
        return self.msg

class TestDidNotRun(Error):
    """Test did not run any subtests."""

class ResourceDenied(unittest.SkipTest):
    """Test skipped because it requested a disallowed resource.

    This is raised when a test calls requires() for a resource that
    has not be enabled.  It is used to distinguish between expected
    and unexpected skips.
    """

def anticipate_failure(condition):
    """Decorator to mark a test that is known to be broken in some cases

       Any use of this decorator should have a comment identifying the
       associated tracker issue.
    """
    if condition:
        return unittest.expectedFailure
    return lambda f: f

def load_package_tests(pkg_dir, loader, standard_tests, pattern):
    """Generic load_tests implementation for simple test packages.

    Most packages can implement load_tests using this function as follows:

       def load_tests(*args):
           return load_package_tests(os.path.dirname(__file__), *args)
    """
    if pattern is None:
        pattern = "test*"
    top_dir = os.path.dirname(              # Lib
                  os.path.dirname(              # test
                      os.path.dirname(__file__)))   # support
    package_tests = loader.discover(start_dir=pkg_dir,
                                    top_level_dir=top_dir,
                                    pattern=pattern)
    standard_tests.addTests(package_tests)
    return standard_tests


def get_attribute(obj, name):
    """Get an attribute, raising SkipTest if AttributeError is raised."""
    try:
        attribute = getattr(obj, name)
    except AttributeError:
        raise unittest.SkipTest("object %r has no attribute %r" % (obj, name))
    else:
        return attribute

verbose = 1              # Flag set to 0 by regrtest.py
use_resources = None     # Flag set to [] by regrtest.py
max_memuse = 0           # Disable bigmem tests (they will still be run with
                         # small sizes, to make sure they work.)
real_max_memuse = 0
junit_xml_list = None    # list of testsuite XML elements
failfast = False

# _original_stdout is meant to hold stdout at the time regrtest began.
# This may be "the real" stdout, or IDLE's emulation of stdout, or whatever.
# The point is to have some flavor of stdout the user can actually see.
_original_stdout = None
def record_original_stdout(stdout):
    global _original_stdout
    _original_stdout = stdout

def get_original_stdout():
    return _original_stdout or sys.stdout


def _force_run(path, func, *args):
    try:
        return func(*args)
    except OSError as err:
        if verbose >= 2:
            print('%s: %s' % (err.__class__.__name__, err))
            print('re-run %s%r' % (func.__name__, args))
        os.chmod(path, stat.S_IRWXU)
        return func(*args)


# Check whether a gui is actually available
def _is_gui_available():
    if hasattr(_is_gui_available, 'result'):
        return _is_gui_available.result
    import platform
    reason = None
    if sys.platform.startswith('win') and platform.win32_is_iot():
        reason = "gui is not available on Windows IoT Core"
    elif sys.platform.startswith('win'):
        # if Python is running as a service (such as the buildbot service),
        # gui interaction may be disallowed
        import ctypes
        import ctypes.wintypes
        UOI_FLAGS = 1
        WSF_VISIBLE = 0x0001
        class USEROBJECTFLAGS(ctypes.Structure):
            _fields_ = [("fInherit", ctypes.wintypes.BOOL),
                        ("fReserved", ctypes.wintypes.BOOL),
                        ("dwFlags", ctypes.wintypes.DWORD)]
        dll = ctypes.windll.user32
        h = dll.GetProcessWindowStation()
        if not h:
            raise ctypes.WinError()
        uof = USEROBJECTFLAGS()
        needed = ctypes.wintypes.DWORD()
        res = dll.GetUserObjectInformationW(h,
            UOI_FLAGS,
            ctypes.byref(uof),
            ctypes.sizeof(uof),
            ctypes.byref(needed))
        if not res:
            raise ctypes.WinError()
        if not bool(uof.dwFlags & WSF_VISIBLE):
            reason = "gui not available (WSF_VISIBLE flag not set)"
    elif sys.platform == 'darwin':
        # The Aqua Tk implementations on OS X can abort the process if
        # being called in an environment where a window server connection
        # cannot be made, for instance when invoked by a buildbot or ssh
        # process not running under the same user id as the current console
        # user.  To avoid that, raise an exception if the window manager
        # connection is not available.
        from ctypes import cdll, c_int, pointer, Structure
        from ctypes.util import find_library

        app_services = cdll.LoadLibrary(find_library("ApplicationServices"))

        if app_services.CGMainDisplayID() == 0:
            reason = "gui tests cannot run without OS X window manager"
        else:
            class ProcessSerialNumber(Structure):
                _fields_ = [("highLongOfPSN", c_int),
                            ("lowLongOfPSN", c_int)]
            psn = ProcessSerialNumber()
            psn_p = pointer(psn)
            if (  (app_services.GetCurrentProcess(psn_p) < 0) or
                  (app_services.SetFrontProcess(psn_p) < 0) ):
                reason = "cannot run without OS X gui process"

    # check on every platform whether tkinter can actually do anything
    if not reason:
        try:
            from tkinter import Tk
            root = Tk()
            root.withdraw()
            root.update()
            root.destroy()
        except Exception as e:
            err_string = str(e)
            if len(err_string) > 50:
                err_string = err_string[:50] + ' [...]'
            reason = 'Tk unavailable due to {}: {}'.format(type(e).__name__,
                                                           err_string)

    _is_gui_available.reason = reason
    _is_gui_available.result = not reason

    return _is_gui_available.result

def is_resource_enabled(resource):
    """Test whether a resource is enabled.

    Known resources are set by regrtest.py.  If not running under regrtest.py,
    all resources are assumed enabled unless use_resources has been set.
    """
    return use_resources is None or resource in use_resources

def requires(resource, msg=None):
    """Raise ResourceDenied if the specified resource is not available."""
    if not is_resource_enabled(resource):
        if msg is None:
            msg = "Use of the %r resource not enabled" % resource
        raise ResourceDenied(msg)
    if resource == 'gui' and not _is_gui_available():
        raise ResourceDenied(_is_gui_available.reason)

def _requires_unix_version(sysname, min_version):
    """Decorator raising SkipTest if the OS is `sysname` and the version is less
    than `min_version`.

    For example, @_requires_unix_version('FreeBSD', (7, 2)) raises SkipTest if
    the FreeBSD version is less than 7.2.
    """
    import platform
    min_version_txt = '.'.join(map(str, min_version))
    version_txt = platform.release().split('-', 1)[0]
    if platform.system() == sysname:
        try:
            version = tuple(map(int, version_txt.split('.')))
        except ValueError:
            skip = False
        else:
            skip = version < min_version
    else:
        skip = False

    return unittest.skipIf(
        skip,
        f"{sysname} version {min_version_txt} or higher required, not "
        f"{version_txt}"
    )


def requires_freebsd_version(*min_version):
    """Decorator raising SkipTest if the OS is FreeBSD and the FreeBSD version is
    less than `min_version`.

    For example, @requires_freebsd_version(7, 2) raises SkipTest if the FreeBSD
    version is less than 7.2.
    """
    return _requires_unix_version('FreeBSD', min_version)

def requires_linux_version(*min_version):
    """Decorator raising SkipTest if the OS is Linux and the Linux version is
    less than `min_version`.

    For example, @requires_linux_version(2, 6, 32) raises SkipTest if the Linux
    version is less than 2.6.32.
    """
    return _requires_unix_version('Linux', min_version)

def requires_mac_ver(*min_version):
    """Decorator raising SkipTest if the OS is Mac OS X and the OS X
    version if less than min_version.

    For example, @requires_mac_ver(10, 5) raises SkipTest if the OS X version
    is lesser than 10.5.
    """
    def decorator(func):
        @functools.wraps(func)
        def wrapper(*args, **kw):
            if sys.platform == 'darwin':
                import platform
                version_txt = platform.mac_ver()[0]
                try:
                    version = tuple(map(int, version_txt.split('.')))
                except ValueError:
                    pass
                else:
                    if version < min_version:
                        min_version_txt = '.'.join(map(str, min_version))
                        raise unittest.SkipTest(
                            "Mac OS X %s or higher required, not %s"
                            % (min_version_txt, version_txt))
            return func(*args, **kw)
        wrapper.min_version = min_version
        return wrapper
    return decorator


def system_must_validate_cert(f):
    """Skip the test on TLS certificate validation failures."""
    @functools.wraps(f)
    def dec(*args, **kwargs):
        try:
            f(*args, **kwargs)
        except OSError as e:
            if "CERTIFICATE_VERIFY_FAILED" in str(e):
                raise unittest.SkipTest("system does not contain "
                                        "necessary certificates")
            raise
    return dec

# A constant likely larger than the underlying OS pipe buffer size, to
# make writes blocking.
# Windows limit seems to be around 512 B, and many Unix kernels have a
# 64 KiB pipe buffer size or 16 * PAGE_SIZE: take a few megs to be sure.
# (see issue #17835 for a discussion of this number).
PIPE_MAX_SIZE = 4 * 1024 * 1024 + 1

# A constant likely larger than the underlying OS socket buffer size, to make
# writes blocking.
# The socket buffer sizes can usually be tuned system-wide (e.g. through sysctl
# on Linux), or on a per-socket basis (SO_SNDBUF/SO_RCVBUF).  See issue #18643
# for a discussion of this number.
SOCK_MAX_SIZE = 16 * 1024 * 1024 + 1

# decorator for skipping tests on non-IEEE 754 platforms
requires_IEEE_754 = unittest.skipUnless(
    float.__getformat__("double").startswith("IEEE"),
    "test requires IEEE 754 doubles")

def requires_zlib(reason='requires zlib'):
    try:
        import zlib
    except ImportError:
        zlib = None
    return unittest.skipUnless(zlib, reason)

def requires_gzip(reason='requires gzip'):
    try:
        import gzip
    except ImportError:
        gzip = None
    return unittest.skipUnless(gzip, reason)

def requires_bz2(reason='requires bz2'):
    try:
        import bz2
    except ImportError:
        bz2 = None
    return unittest.skipUnless(bz2, reason)

def requires_lzma(reason='requires lzma'):
    try:
        import lzma
    except ImportError:
        lzma = None
    return unittest.skipUnless(lzma, reason)

requires_legacy_unicode_capi = unittest.skipUnless(unicode_legacy_string,
                        'requires legacy Unicode C API')

is_jython = sys.platform.startswith('java')

is_android = hasattr(sys, 'getandroidapilevel')

if sys.platform not in ('win32', 'vxworks'):
    unix_shell = '/system/bin/sh' if is_android else '/bin/sh'
else:
    unix_shell = None

# Define the URL of a dedicated HTTP server for the network tests.
# The URL must use clear-text HTTP: no redirection to encrypted HTTPS.
TEST_HTTP_URL = "http://www.pythontest.net"

# Set by libregrtest/main.py so we can skip tests that are not
# useful for PGO
PGO = False

# Set by libregrtest/main.py if we are running the extended (time consuming)
# PGO task.  If this is True, PGO is also True.
PGO_EXTENDED = False

# TEST_HOME_DIR refers to the top level directory of the "test" package
# that contains Python's regression test suite
TEST_SUPPORT_DIR = os.path.dirname(os.path.abspath(__file__))
TEST_HOME_DIR = os.path.dirname(TEST_SUPPORT_DIR)

# TEST_DATA_DIR is used as a target download location for remote resources
TEST_DATA_DIR = os.path.join(TEST_HOME_DIR, "data")


def darwin_malloc_err_warning(test_name):
    """Assure user that loud errors generated by macOS libc's malloc are
    expected."""
    if sys.platform != 'darwin':
        return

    import shutil
    msg = ' NOTICE '
    detail = (f'{test_name} may generate "malloc can\'t allocate region"\n'
              'warnings on macOS systems. This behavior is known. Do not\n'
              'report a bug unless tests are also failing. See bpo-40928.')

    padding, _ = shutil.get_terminal_size()
    print(msg.center(padding, '-'))
    print(detail)
    print('-' * padding)


def findfile(filename, subdir=None):
    """Try to find a file on sys.path or in the test directory.  If it is not
    found the argument passed to the function is returned (this does not
    necessarily signal failure; could still be the legitimate path).

    Setting *subdir* indicates a relative path to use to find the file
    rather than looking directly in the path directories.
    """
    if os.path.isabs(filename):
        return filename
    if subdir is not None:
        filename = os.path.join(subdir, filename)
    path = [TEST_HOME_DIR] + sys.path
    for dn in path:
        fn = os.path.join(dn, filename)
        if os.path.exists(fn): return fn
    return filename


def sortdict(dict):
    "Like repr(dict), but in sorted order."
    items = sorted(dict.items())
    reprpairs = ["%r: %r" % pair for pair in items]
    withcommas = ", ".join(reprpairs)
    return "{%s}" % withcommas

def check_syntax_error(testcase, statement, errtext='', *, lineno=None, offset=None):
    with testcase.assertRaisesRegex(SyntaxError, errtext) as cm:
        compile(statement, '<test string>', 'exec')
    err = cm.exception
    testcase.assertIsNotNone(err.lineno)
    if lineno is not None:
        testcase.assertEqual(err.lineno, lineno)
    testcase.assertIsNotNone(err.offset)
    if offset is not None:
        testcase.assertEqual(err.offset, offset)


def open_urlresource(url, *args, **kw):
    import urllib.request, urllib.parse
    from .os_helper import unlink
    try:
        import gzip
    except ImportError:
        gzip = None

    check = kw.pop('check', None)

    filename = urllib.parse.urlparse(url)[2].split('/')[-1] # '/': it's URL!

    fn = os.path.join(TEST_DATA_DIR, filename)

    def check_valid_file(fn):
        f = open(fn, *args, **kw)
        if check is None:
            return f
        elif check(f):
            f.seek(0)
            return f
        f.close()

    if os.path.exists(fn):
        f = check_valid_file(fn)
        if f is not None:
            return f
        unlink(fn)

    # Verify the requirement before downloading the file
    requires('urlfetch')

    if verbose:
        print('\tfetching %s ...' % url, file=get_original_stdout())
    opener = urllib.request.build_opener()
    if gzip:
        opener.addheaders.append(('Accept-Encoding', 'gzip'))
    f = opener.open(url, timeout=INTERNET_TIMEOUT)
    if gzip and f.headers.get('Content-Encoding') == 'gzip':
        f = gzip.GzipFile(fileobj=f)
    try:
        with open(fn, "wb") as out:
            s = f.read()
            while s:
                out.write(s)
                s = f.read()
    finally:
        f.close()

    f = check_valid_file(fn)
    if f is not None:
        return f
    raise TestFailed('invalid resource %r' % fn)


@contextlib.contextmanager
def captured_output(stream_name):
    """Return a context manager used by captured_stdout/stdin/stderr
    that temporarily replaces the sys stream *stream_name* with a StringIO."""
    import io
    orig_stdout = getattr(sys, stream_name)
    setattr(sys, stream_name, io.StringIO())
    try:
        yield getattr(sys, stream_name)
    finally:
        setattr(sys, stream_name, orig_stdout)

def captured_stdout():
    """Capture the output of sys.stdout:

       with captured_stdout() as stdout:
           print("hello")
       self.assertEqual(stdout.getvalue(), "hello\\n")
    """
    return captured_output("stdout")

def captured_stderr():
    """Capture the output of sys.stderr:

       with captured_stderr() as stderr:
           print("hello", file=sys.stderr)
       self.assertEqual(stderr.getvalue(), "hello\\n")
    """
    return captured_output("stderr")

def captured_stdin():
    """Capture the input to sys.stdin:

       with captured_stdin() as stdin:
           stdin.write('hello\\n')
           stdin.seek(0)
           # call test code that consumes from sys.stdin
           captured = input()
       self.assertEqual(captured, "hello")
    """
    return captured_output("stdin")


def gc_collect():
    """Force as many objects as possible to be collected.

    In non-CPython implementations of Python, this is needed because timely
    deallocation is not guaranteed by the garbage collector.  (Even in CPython
    this can be the case in case of reference cycles.)  This means that __del__
    methods may be called later than expected and weakrefs may remain alive for
    longer than expected.  This function tries its best to force all garbage
    objects to disappear.
    """
    import gc
    gc.collect()
    if is_jython:
        time.sleep(0.1)
    gc.collect()
    gc.collect()

@contextlib.contextmanager
def disable_gc():
    import gc
    have_gc = gc.isenabled()
    gc.disable()
    try:
        yield
    finally:
        if have_gc:
            gc.enable()


def python_is_optimized():
    """Find if Python was built with optimizations."""
    cflags = sysconfig.get_config_var('PY_CFLAGS') or ''
    final_opt = ""
    for opt in cflags.split():
        if opt.startswith('-O'):
            final_opt = opt
    return final_opt not in ('', '-O0', '-Og')


_header = 'nP'
_align = '0n'
if hasattr(sys, "getobjects"):
    _header = '2P' + _header
    _align = '0P'
_vheader = _header + 'n'

def calcobjsize(fmt):
    import struct
    return struct.calcsize(_header + fmt + _align)

def calcvobjsize(fmt):
    import struct
    return struct.calcsize(_vheader + fmt + _align)


_TPFLAGS_HAVE_GC = 1<<14
_TPFLAGS_HEAPTYPE = 1<<9

def check_sizeof(test, o, size):
    import _testinternalcapi
    result = sys.getsizeof(o)
    # add GC header size
    if ((type(o) == type) and (o.__flags__ & _TPFLAGS_HEAPTYPE) or\
        ((type(o) != type) and (type(o).__flags__ & _TPFLAGS_HAVE_GC))):
        size += _testinternalcapi.SIZEOF_PYGC_HEAD
    msg = 'wrong size for %s: got %d, expected %d' \
            % (type(o), result, size)
    test.assertEqual(result, size, msg)

#=======================================================================
# Decorator for running a function in a different locale, correctly resetting
# it afterwards.

@contextlib.contextmanager
def run_with_locale(catstr, *locales):
            try:
                import locale
                category = getattr(locale, catstr)
                orig_locale = locale.setlocale(category)
            except AttributeError:
                # if the test author gives us an invalid category string
                raise
            except:
                # cannot retrieve original locale, so do nothing
                locale = orig_locale = None
            else:
                for loc in locales:
                    try:
                        locale.setlocale(category, loc)
                        break
                    except:
                        pass

            try:
                yield
            finally:
                if locale and orig_locale:
                    locale.setlocale(category, orig_locale)

#=======================================================================
# Decorator for running a function in a specific timezone, correctly
# resetting it afterwards.

def run_with_tz(tz):
    def decorator(func):
        def inner(*args, **kwds):
            try:
                tzset = time.tzset
            except AttributeError:
                raise unittest.SkipTest("tzset required")
            if 'TZ' in os.environ:
                orig_tz = os.environ['TZ']
            else:
                orig_tz = None
            os.environ['TZ'] = tz
            tzset()

            # now run the function, resetting the tz on exceptions
            try:
                return func(*args, **kwds)
            finally:
                if orig_tz is None:
                    del os.environ['TZ']
                else:
                    os.environ['TZ'] = orig_tz
                time.tzset()

        inner.__name__ = func.__name__
        inner.__doc__ = func.__doc__
        return inner
    return decorator

#=======================================================================
# Big-memory-test support. Separate from 'resources' because memory use
# should be configurable.

# Some handy shorthands. Note that these are used for byte-limits as well
# as size-limits, in the various bigmem tests
_1M = 1024*1024
_1G = 1024 * _1M
_2G = 2 * _1G
_4G = 4 * _1G

MAX_Py_ssize_t = sys.maxsize

def set_memlimit(limit):
    global max_memuse
    global real_max_memuse
    sizes = {
        'k': 1024,
        'm': _1M,
        'g': _1G,
        't': 1024*_1G,
    }
    m = re.match(r'(\d+(\.\d+)?) (K|M|G|T)b?$', limit,
                 re.IGNORECASE | re.VERBOSE)
    if m is None:
        raise ValueError('Invalid memory limit %r' % (limit,))
    memlimit = int(float(m.group(1)) * sizes[m.group(3).lower()])
    real_max_memuse = memlimit
    if memlimit > MAX_Py_ssize_t:
        memlimit = MAX_Py_ssize_t
    if memlimit < _2G - 1:
        raise ValueError('Memory limit %r too low to be useful' % (limit,))
    max_memuse = memlimit

class _MemoryWatchdog:
    """An object which periodically watches the process' memory consumption
    and prints it out.
    """

    def __init__(self):
        self.procfile = '/proc/{pid}/statm'.format(pid=os.getpid())
        self.started = False

    def start(self):
        import warnings
        try:
            f = open(self.procfile, 'r')
        except OSError as e:
            warnings.warn('/proc not available for stats: {}'.format(e),
                          RuntimeWarning)
            sys.stderr.flush()
            return

        import subprocess
        with f:
            watchdog_script = findfile("memory_watchdog.py")
            self.mem_watchdog = subprocess.Popen([sys.executable, watchdog_script],
                                                 stdin=f,
                                                 stderr=subprocess.DEVNULL)
        self.started = True

    def stop(self):
        if self.started:
            self.mem_watchdog.terminate()
            self.mem_watchdog.wait()


def bigmemtest(size, memuse, dry_run=True):
    """Decorator for bigmem tests.

    'size' is a requested size for the test (in arbitrary, test-interpreted
    units.) 'memuse' is the number of bytes per unit for the test, or a good
    estimate of it. For example, a test that needs two byte buffers, of 4 GiB
    each, could be decorated with @bigmemtest(size=_4G, memuse=2).

    The 'size' argument is normally passed to the decorated test method as an
    extra argument. If 'dry_run' is true, the value passed to the test method
    may be less than the requested value. If 'dry_run' is false, it means the
    test doesn't support dummy runs when -M is not specified.
    """
    def decorator(f):
        def wrapper(self):
            size = wrapper.size
            memuse = wrapper.memuse
            if not real_max_memuse:
                maxsize = 5147
            else:
                maxsize = size

            if ((real_max_memuse or not dry_run)
                and real_max_memuse < maxsize * memuse):
                raise unittest.SkipTest(
                    "not enough memory: %.1fG minimum needed"
                    % (size * memuse / (1024 ** 3)))

            if real_max_memuse and verbose:
                print()
                print(" ... expected peak memory use: {peak:.1f}G"
                      .format(peak=size * memuse / (1024 ** 3)))
                watchdog = _MemoryWatchdog()
                watchdog.start()
            else:
                watchdog = None

            try:
                return f(self, maxsize)
            finally:
                if watchdog:
                    watchdog.stop()

        wrapper.size = size
        wrapper.memuse = memuse
        return wrapper
    return decorator

def bigaddrspacetest(f):
    """Decorator for tests that fill the address space."""
    def wrapper(self):
        if max_memuse < MAX_Py_ssize_t:
            if MAX_Py_ssize_t >= 2**63 - 1 and max_memuse >= 2**31:
                raise unittest.SkipTest(
                    "not enough memory: try a 32-bit build instead")
            else:
                raise unittest.SkipTest(
                    "not enough memory: %.1fG minimum needed"
                    % (MAX_Py_ssize_t / (1024 ** 3)))
        else:
            return f(self)
    return wrapper

#=======================================================================
# unittest integration.

class BasicTestRunner:
    def run(self, test):
        result = unittest.TestResult()
        test(result)
        return result

def _id(obj):
    return obj

def requires_resource(resource):
    if resource == 'gui' and not _is_gui_available():
        return unittest.skip(_is_gui_available.reason)
    if is_resource_enabled(resource):
        return _id
    else:
        return unittest.skip("resource {0!r} is not enabled".format(resource))

def cpython_only(test):
    """
    Decorator for tests only applicable on CPython.
    """
    return impl_detail(cpython=True)(test)

def impl_detail(msg=None, **guards):
    if check_impl_detail(**guards):
        return _id
    if msg is None:
        guardnames, default = _parse_guards(guards)
        if default:
            msg = "implementation detail not available on {0}"
        else:
            msg = "implementation detail specific to {0}"
        guardnames = sorted(guardnames.keys())
        msg = msg.format(' or '.join(guardnames))
    return unittest.skip(msg)

def _parse_guards(guards):
    # Returns a tuple ({platform_name: run_me}, default_value)
    if not guards:
        return ({'cpython': True}, False)
    is_true = list(guards.values())[0]
    assert list(guards.values()) == [is_true] * len(guards)   # all True or all False
    return (guards, not is_true)

# Use the following check to guard CPython's implementation-specific tests --
# or to run them only on the implementation(s) guarded by the arguments.
def check_impl_detail(**guards):
    """This function returns True or False depending on the host platform.
       Examples:
          if check_impl_detail():               # only on CPython (default)
          if check_impl_detail(jython=True):    # only on Jython
          if check_impl_detail(cpython=False):  # everywhere except on CPython
    """
    guards, default = _parse_guards(guards)
    return guards.get(sys.implementation.name, default)


def no_tracing(func):
    """Decorator to temporarily turn off tracing for the duration of a test."""
    if not hasattr(sys, 'gettrace'):
        return func
    else:
        @functools.wraps(func)
        def wrapper(*args, **kwargs):
            original_trace = sys.gettrace()
            try:
                sys.settrace(None)
                return func(*args, **kwargs)
            finally:
                sys.settrace(original_trace)
        return wrapper


def refcount_test(test):
    """Decorator for tests which involve reference counting.

    To start, the decorator does not run the test if is not run by CPython.
    After that, any trace function is unset during the test to prevent
    unexpected refcounts caused by the trace function.

    """
    return no_tracing(cpython_only(test))


def _filter_suite(suite, pred):
    """Recursively filter test cases in a suite based on a predicate."""
    newtests = []
    for test in suite._tests:
        if isinstance(test, unittest.TestSuite):
            _filter_suite(test, pred)
            newtests.append(test)
        else:
            if pred(test):
                newtests.append(test)
    suite._tests = newtests

def _run_suite(suite):
    """Run tests from a unittest.TestSuite-derived class."""
    runner = get_test_runner(sys.stdout,
                             verbosity=verbose,
                             capture_output=(junit_xml_list is not None))

    result = runner.run(suite)

    if junit_xml_list is not None:
        junit_xml_list.append(result.get_xml_element())

    if not result.testsRun and not result.skipped:
        raise TestDidNotRun
    if not result.wasSuccessful():
        if len(result.errors) == 1 and not result.failures:
            err = result.errors[0][1]
        elif len(result.failures) == 1 and not result.errors:
            err = result.failures[0][1]
        else:
            err = "multiple errors occurred"
            if not verbose: err += "; run in verbose mode for details"
        errors = [(str(tc), exc_str) for tc, exc_str in result.errors]
        failures = [(str(tc), exc_str) for tc, exc_str in result.failures]
        raise TestFailedWithDetails(err, errors, failures)


# By default, don't filter tests
_match_test_func = None

_accept_test_patterns = None
_ignore_test_patterns = None


def match_test(test):
    # Function used by support.run_unittest() and regrtest --list-cases
    if _match_test_func is None:
        return True
    else:
        return _match_test_func(test.id())


def _is_full_match_test(pattern):
    # If a pattern contains at least one dot, it's considered
    # as a full test identifier.
    # Example: 'test.test_os.FileTests.test_access'.
    #
    # ignore patterns which contain fnmatch patterns: '*', '?', '[...]'
    # or '[!...]'. For example, ignore 'test_access*'.
    return ('.' in pattern) and (not re.search(r'[?*\[\]]', pattern))


def set_match_tests(accept_patterns=None, ignore_patterns=None):
    global _match_test_func, _accept_test_patterns, _ignore_test_patterns


    if accept_patterns is None:
        accept_patterns = ()
    if ignore_patterns is None:
        ignore_patterns = ()

    accept_func = ignore_func = None

    if accept_patterns != _accept_test_patterns:
        accept_patterns, accept_func = _compile_match_function(accept_patterns)
    if ignore_patterns != _ignore_test_patterns:
        ignore_patterns, ignore_func = _compile_match_function(ignore_patterns)

    # Create a copy since patterns can be mutable and so modified later
    _accept_test_patterns = tuple(accept_patterns)
    _ignore_test_patterns = tuple(ignore_patterns)

    if accept_func is not None or ignore_func is not None:
        def match_function(test_id):
            accept = True
            ignore = False
            if accept_func:
                accept = accept_func(test_id)
            if ignore_func:
                ignore = ignore_func(test_id)
            return accept and not ignore

        _match_test_func = match_function


def _compile_match_function(patterns):
    if not patterns:
        func = None
        # set_match_tests(None) behaves as set_match_tests(())
        patterns = ()
    elif all(map(_is_full_match_test, patterns)):
        # Simple case: all patterns are full test identifier.
        # The test.bisect_cmd utility only uses such full test identifiers.
        func = set(patterns).__contains__
    else:
        import fnmatch
        regex = '|'.join(map(fnmatch.translate, patterns))
        # The search *is* case sensitive on purpose:
        # don't use flags=re.IGNORECASE
        regex_match = re.compile(regex).match

        def match_test_regex(test_id):
            if regex_match(test_id):
                # The regex matches the whole identifier, for example
                # 'test.test_os.FileTests.test_access'.
                return True
            else:
                # Try to match parts of the test identifier.
                # For example, split 'test.test_os.FileTests.test_access'
                # into: 'test', 'test_os', 'FileTests' and 'test_access'.
                return any(map(regex_match, test_id.split(".")))

        func = match_test_regex

    return patterns, func


def run_unittest(*classes):
    """Run tests from unittest.TestCase-derived classes."""
    valid_types = (unittest.TestSuite, unittest.TestCase)
    suite = unittest.TestSuite()
    for cls in classes:
        if isinstance(cls, str):
            if cls in sys.modules:
                suite.addTest(unittest.findTestCases(sys.modules[cls]))
            else:
                raise ValueError("str arguments must be keys in sys.modules")
        elif isinstance(cls, valid_types):
            suite.addTest(cls)
        else:
            suite.addTest(unittest.makeSuite(cls))
    _filter_suite(suite, match_test)
    _run_suite(suite)

#=======================================================================
# Check for the presence of docstrings.

# Rather than trying to enumerate all the cases where docstrings may be
# disabled, we just check for that directly

def _check_docstrings():
    """Just used to check if docstrings are enabled"""

MISSING_C_DOCSTRINGS = (check_impl_detail() and
                        sys.platform != 'win32' and
                        not sysconfig.get_config_var('WITH_DOC_STRINGS'))

HAVE_DOCSTRINGS = (_check_docstrings.__doc__ is not None and
                   not MISSING_C_DOCSTRINGS)

requires_docstrings = unittest.skipUnless(HAVE_DOCSTRINGS,
                                          "test requires docstrings")


#=======================================================================
# doctest driver.

def run_doctest(module, verbosity=None, optionflags=0):
    """Run doctest on the given module.  Return (#failures, #tests).

    If optional argument verbosity is not specified (or is None), pass
    support's belief about verbosity on to doctest.  Else doctest's
    usual behavior is used (it searches sys.argv for -v).
    """

    import doctest

    if verbosity is None:
        verbosity = verbose
    else:
        verbosity = None

    f, t = doctest.testmod(module, verbose=verbosity, optionflags=optionflags)
    if f:
        raise TestFailed("%d of %d doctests failed" % (f, t))
    if verbose:
        print('doctest (%s) ... %d tests with zero failures' %
              (module.__name__, t))
    return f, t


#=======================================================================
# Support for saving and restoring the imported modules.

def print_warning(msg):
    # bpo-39983: Print into sys.__stderr__ to display the warning even
    # when sys.stderr is captured temporarily by a test
    for line in msg.splitlines():
        print(f"Warning -- {line}", file=sys.__stderr__, flush=True)


# Flag used by saved_test_environment of test.libregrtest.save_env,
# to check if a test modified the environment. The flag should be set to False
# before running a new test.
#
# For example, threading_helper.threading_cleanup() sets the flag is the function fails
# to cleanup threads.
environment_altered = False

def reap_children():
    """Use this function at the end of test_main() whenever sub-processes
    are started.  This will help ensure that no extra children (zombies)
    stick around to hog resources and create problems when looking
    for refleaks.
    """
    global environment_altered

    # Need os.waitpid(-1, os.WNOHANG): Windows is not supported
    if not (hasattr(os, 'waitpid') and hasattr(os, 'WNOHANG')):
        return

    # Reap all our dead child processes so we don't leave zombies around.
    # These hog resources and might be causing some of the buildbots to die.
    while True:
        try:
            # Read the exit status of any child process which already completed
            pid, status = os.waitpid(-1, os.WNOHANG)
        except OSError:
            break

        if pid == 0:
            break

        print_warning(f"reap_children() reaped child process {pid}")
        environment_altered = True


@contextlib.contextmanager
def swap_attr(obj, attr, new_val):
    """Temporary swap out an attribute with a new object.

    Usage:
        with swap_attr(obj, "attr", 5):
            ...

        This will set obj.attr to 5 for the duration of the with: block,
        restoring the old value at the end of the block. If `attr` doesn't
        exist on `obj`, it will be created and then deleted at the end of the
        block.

        The old value (or None if it doesn't exist) will be assigned to the
        target of the "as" clause, if there is one.
    """
    if hasattr(obj, attr):
        real_val = getattr(obj, attr)
        setattr(obj, attr, new_val)
        try:
            yield real_val
        finally:
            setattr(obj, attr, real_val)
    else:
        setattr(obj, attr, new_val)
        try:
            yield
        finally:
            if hasattr(obj, attr):
                delattr(obj, attr)

@contextlib.contextmanager
def swap_item(obj, item, new_val):
    """Temporary swap out an item with a new object.

    Usage:
        with swap_item(obj, "item", 5):
            ...

        This will set obj["item"] to 5 for the duration of the with: block,
        restoring the old value at the end of the block. If `item` doesn't
        exist on `obj`, it will be created and then deleted at the end of the
        block.

        The old value (or None if it doesn't exist) will be assigned to the
        target of the "as" clause, if there is one.
    """
    if item in obj:
        real_val = obj[item]
        obj[item] = new_val
        try:
            yield real_val
        finally:
            obj[item] = real_val
    else:
        obj[item] = new_val
        try:
            yield
        finally:
            if item in obj:
                del obj[item]

def args_from_interpreter_flags():
    """Return a list of command-line arguments reproducing the current
    settings in sys.flags and sys.warnoptions."""
    import subprocess
    return subprocess._args_from_interpreter_flags()

def optim_args_from_interpreter_flags():
    """Return a list of command-line arguments reproducing the current
    optimization settings in sys.flags."""
    import subprocess
    return subprocess._optim_args_from_interpreter_flags()


class Matcher(object):

    _partial_matches = ('msg', 'message')

    def matches(self, d, **kwargs):
        """
        Try to match a single dict with the supplied arguments.

        Keys whose values are strings and which are in self._partial_matches
        will be checked for partial (i.e. substring) matches. You can extend
        this scheme to (for example) do regular expression matching, etc.
        """
        result = True
        for k in kwargs:
            v = kwargs[k]
            dv = d.get(k)
            if not self.match_value(k, dv, v):
                result = False
                break
        return result

    def match_value(self, k, dv, v):
        """
        Try to match a single stored value (dv) with a supplied value (v).
        """
        if type(v) != type(dv):
            result = False
        elif type(dv) is not str or k not in self._partial_matches:
            result = (v == dv)
        else:
            result = dv.find(v) >= 0
        return result


_buggy_ucrt = None
def skip_if_buggy_ucrt_strfptime(test):
    """
    Skip decorator for tests that use buggy strptime/strftime

    If the UCRT bugs are present time.localtime().tm_zone will be
    an empty string, otherwise we assume the UCRT bugs are fixed

    See bpo-37552 [Windows] strptime/strftime return invalid
    results with UCRT version 17763.615
    """
    import locale
    global _buggy_ucrt
    if _buggy_ucrt is None:
        if(sys.platform == 'win32' and
                locale.getdefaultlocale()[1]  == 'cp65001' and
                time.localtime().tm_zone == ''):
            _buggy_ucrt = True
        else:
            _buggy_ucrt = False
    return unittest.skip("buggy MSVC UCRT strptime/strftime")(test) if _buggy_ucrt else test

class PythonSymlink:
    """Creates a symlink for the current Python executable"""
    def __init__(self, link=None):
        from .os_helper import TESTFN

        self.link = link or os.path.abspath(TESTFN)
        self._linked = []
        self.real = os.path.realpath(sys.executable)
        self._also_link = []

        self._env = None

        self._platform_specific()

    def _platform_specific(self):
        pass

    if sys.platform == "win32":
        def _platform_specific(self):
            import glob
            import _winapi

            if os.path.lexists(self.real) and not os.path.exists(self.real):
                # App symlink appears to not exist, but we want the
                # real executable here anyway
                self.real = _winapi.GetModuleFileName(0)

            dll = _winapi.GetModuleFileName(sys.dllhandle)
            src_dir = os.path.dirname(dll)
            dest_dir = os.path.dirname(self.link)
            self._also_link.append((
                dll,
                os.path.join(dest_dir, os.path.basename(dll))
            ))
            for runtime in glob.glob(os.path.join(glob.escape(src_dir), "vcruntime*.dll")):
                self._also_link.append((
                    runtime,
                    os.path.join(dest_dir, os.path.basename(runtime))
                ))

            self._env = {k.upper(): os.getenv(k) for k in os.environ}
            self._env["PYTHONHOME"] = os.path.dirname(self.real)
            if sysconfig.is_python_build(True):
                self._env["PYTHONPATH"] = os.path.dirname(os.__file__)

    def __enter__(self):
        os.symlink(self.real, self.link)
        self._linked.append(self.link)
        for real, link in self._also_link:
            os.symlink(real, link)
            self._linked.append(link)
        return self

    def __exit__(self, exc_type, exc_value, exc_tb):
        for link in self._linked:
            try:
                os.remove(link)
            except IOError as ex:
                if verbose:
                    print("failed to clean up {}: {}".format(link, ex))

    def _call(self, python, args, env, returncode):
        import subprocess
        cmd = [python, *args]
        p = subprocess.Popen(cmd, stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE, env=env)
        r = p.communicate()
        if p.returncode != returncode:
            if verbose:
                print(repr(r[0]))
                print(repr(r[1]), file=sys.stderr)
            raise RuntimeError(
                'unexpected return code: {0} (0x{0:08X})'.format(p.returncode))
        return r

    def call_real(self, *args, returncode=0):
        return self._call(self.real, args, None, returncode)

    def call_link(self, *args, returncode=0):
        return self._call(self.link, args, self._env, returncode)


def skip_if_pgo_task(test):
    """Skip decorator for tests not run in (non-extended) PGO task"""
    ok = not PGO or PGO_EXTENDED
    msg = "Not run for (non-extended) PGO task"
    return test if ok else unittest.skip(msg)(test)


def detect_api_mismatch(ref_api, other_api, *, ignore=()):
    """Returns the set of items in ref_api not in other_api, except for a
    defined list of items to be ignored in this check.

    By default this skips private attributes beginning with '_' but
    includes all magic methods, i.e. those starting and ending in '__'.
    """
    missing_items = set(dir(ref_api)) - set(dir(other_api))
    if ignore:
        missing_items -= set(ignore)
    missing_items = set(m for m in missing_items
                        if not m.startswith('_') or m.endswith('__'))
    return missing_items


def check__all__(test_case, module, name_of_module=None, extra=(),
                 not_exported=()):
    """Assert that the __all__ variable of 'module' contains all public names.

    The module's public names (its API) are detected automatically based on
    whether they match the public name convention and were defined in
    'module'.

    The 'name_of_module' argument can specify (as a string or tuple thereof)
    what module(s) an API could be defined in in order to be detected as a
    public API. One case for this is when 'module' imports part of its public
    API from other modules, possibly a C backend (like 'csv' and its '_csv').

    The 'extra' argument can be a set of names that wouldn't otherwise be
    automatically detected as "public", like objects without a proper
    '__module__' attribute. If provided, it will be added to the
    automatically detected ones.

    The 'not_exported' argument can be a set of names that must not be treated
    as part of the public API even though their names indicate otherwise.

    Usage:
        import bar
        import foo
        import unittest
        from test import support

        class MiscTestCase(unittest.TestCase):
            def test__all__(self):
                support.check__all__(self, foo)

        class OtherTestCase(unittest.TestCase):
            def test__all__(self):
                extra = {'BAR_CONST', 'FOO_CONST'}
                not_exported = {'baz'}  # Undocumented name.
                # bar imports part of its API from _bar.
                support.check__all__(self, bar, ('bar', '_bar'),
                                     extra=extra, not_exported=not_exported)

    """

    if name_of_module is None:
        name_of_module = (module.__name__, )
    elif isinstance(name_of_module, str):
        name_of_module = (name_of_module, )

    expected = set(extra)

    for name in dir(module):
        if name.startswith('_') or name in not_exported:
            continue
        obj = getattr(module, name)
        if (getattr(obj, '__module__', None) in name_of_module or
                (not hasattr(obj, '__module__') and
                 not isinstance(obj, types.ModuleType))):
            expected.add(name)
    test_case.assertCountEqual(module.__all__, expected)


def suppress_msvcrt_asserts(verbose=False):
    try:
        import msvcrt
    except ImportError:
        return

    msvcrt.SetErrorMode(msvcrt.SEM_FAILCRITICALERRORS
                        | msvcrt.SEM_NOALIGNMENTFAULTEXCEPT
                        | msvcrt.SEM_NOGPFAULTERRORBOX
                        | msvcrt.SEM_NOOPENFILEERRORBOX)

    # CrtSetReportMode() is only available in debug build
    if hasattr(msvcrt, 'CrtSetReportMode'):
        for m in [msvcrt.CRT_WARN, msvcrt.CRT_ERROR, msvcrt.CRT_ASSERT]:
            if verbose:
                msvcrt.CrtSetReportMode(m, msvcrt.CRTDBG_MODE_FILE)
                msvcrt.CrtSetReportFile(m, msvcrt.CRTDBG_FILE_STDERR)
            else:
                msvcrt.CrtSetReportMode(m, 0)


class SuppressCrashReport:
    """Try to prevent a crash report from popping up.

    On Windows, don't display the Windows Error Reporting dialog.  On UNIX,
    disable the creation of coredump file.
    """
    old_value = None
    old_modes = None

    def __enter__(self):
        """On Windows, disable Windows Error Reporting dialogs using
        SetErrorMode() and CrtSetReportMode().

        On UNIX, try to save the previous core file size limit, then set
        soft limit to 0.
        """
        if sys.platform.startswith('win'):
            # see http://msdn.microsoft.com/en-us/library/windows/desktop/ms680621.aspx
            try:
                import msvcrt
            except ImportError:
                return

            self.old_value = msvcrt.GetErrorMode()

            msvcrt.SetErrorMode(self.old_value | msvcrt.SEM_NOGPFAULTERRORBOX)

            # bpo-23314: Suppress assert dialogs in debug builds.
            # CrtSetReportMode() is only available in debug build.
            if hasattr(msvcrt, 'CrtSetReportMode'):
                self.old_modes = {}
                for report_type in [msvcrt.CRT_WARN,
                                    msvcrt.CRT_ERROR,
                                    msvcrt.CRT_ASSERT]:
                    old_mode = msvcrt.CrtSetReportMode(report_type,
                            msvcrt.CRTDBG_MODE_FILE)
                    old_file = msvcrt.CrtSetReportFile(report_type,
                            msvcrt.CRTDBG_FILE_STDERR)
                    self.old_modes[report_type] = old_mode, old_file

        else:
            try:
                import resource
                self.resource = resource
            except ImportError:
                self.resource = None
            if self.resource is not None:
                try:
                    self.old_value = self.resource.getrlimit(self.resource.RLIMIT_CORE)
                    self.resource.setrlimit(self.resource.RLIMIT_CORE,
                                            (0, self.old_value[1]))
                except (ValueError, OSError):
                    pass

            if sys.platform == 'darwin':
                import subprocess
                # Check if the 'Crash Reporter' on OSX was configured
                # in 'Developer' mode and warn that it will get triggered
                # when it is.
                #
                # This assumes that this context manager is used in tests
                # that might trigger the next manager.
                cmd = ['/usr/bin/defaults', 'read',
                       'com.apple.CrashReporter', 'DialogType']
                proc = subprocess.Popen(cmd,
                                        stdout=subprocess.PIPE,
                                        stderr=subprocess.PIPE)
                with proc:
                    stdout = proc.communicate()[0]
                if stdout.strip() == b'developer':
                    print("this test triggers the Crash Reporter, "
                          "that is intentional", end='', flush=True)

        return self

    def __exit__(self, *ignore_exc):
        """Restore Windows ErrorMode or core file behavior to initial value."""
        if self.old_value is None:
            return

        if sys.platform.startswith('win'):
            import msvcrt
            msvcrt.SetErrorMode(self.old_value)

            if self.old_modes:
                for report_type, (old_mode, old_file) in self.old_modes.items():
                    msvcrt.CrtSetReportMode(report_type, old_mode)
                    msvcrt.CrtSetReportFile(report_type, old_file)
        else:
            if self.resource is not None:
                try:
                    self.resource.setrlimit(self.resource.RLIMIT_CORE, self.old_value)
                except (ValueError, OSError):
                    pass


def patch(test_instance, object_to_patch, attr_name, new_value):
    """Override 'object_to_patch'.'attr_name' with 'new_value'.

    Also, add a cleanup procedure to 'test_instance' to restore
    'object_to_patch' value for 'attr_name'.
    The 'attr_name' should be a valid attribute for 'object_to_patch'.

    """
    # check that 'attr_name' is a real attribute for 'object_to_patch'
    # will raise AttributeError if it does not exist
    getattr(object_to_patch, attr_name)

    # keep a copy of the old value
    attr_is_local = False
    try:
        old_value = object_to_patch.__dict__[attr_name]
    except (AttributeError, KeyError):
        old_value = getattr(object_to_patch, attr_name, None)
    else:
        attr_is_local = True

    # restore the value when the test is done
    def cleanup():
        if attr_is_local:
            setattr(object_to_patch, attr_name, old_value)
        else:
            delattr(object_to_patch, attr_name)

    test_instance.addCleanup(cleanup)

    # actually override the attribute
    setattr(object_to_patch, attr_name, new_value)


def run_in_subinterp(code):
    """
    Run code in a subinterpreter. Raise unittest.SkipTest if the tracemalloc
    module is enabled.
    """
    # Issue #10915, #15751: PyGILState_*() functions don't work with
    # sub-interpreters, the tracemalloc module uses these functions internally
    try:
        import tracemalloc
    except ImportError:
        pass
    else:
        if tracemalloc.is_tracing():
            raise unittest.SkipTest("run_in_subinterp() cannot be used "
                                     "if tracemalloc module is tracing "
                                     "memory allocations")
    import _testcapi
    return _testcapi.run_in_subinterp(code)


def check_free_after_iterating(test, iter, cls, args=()):
    class A(cls):
        def __del__(self):
            nonlocal done
            done = True
            try:
                next(it)
            except StopIteration:
                pass

    done = False
    it = iter(A(*args))
    # Issue 26494: Shouldn't crash
    test.assertRaises(StopIteration, next, it)
    # The sequence should be deallocated just after the end of iterating
    gc_collect()
    test.assertTrue(done)


def missing_compiler_executable(cmd_names=[]):
    """Check if the compiler components used to build the interpreter exist.

    Check for the existence of the compiler executables whose names are listed
    in 'cmd_names' or all the compiler executables when 'cmd_names' is empty
    and return the first missing executable or None when none is found
    missing.

    """
    # TODO (PEP 632): alternate check without using distutils
    from distutils import ccompiler, sysconfig, spawn, errors
    compiler = ccompiler.new_compiler()
    sysconfig.customize_compiler(compiler)
    if compiler.compiler_type == "msvc":
        # MSVC has no executables, so check whether initialization succeeds
        try:
            compiler.initialize()
        except errors.DistutilsPlatformError:
            return "msvc"
    for name in compiler.executables:
        if cmd_names and name not in cmd_names:
            continue
        cmd = getattr(compiler, name)
        if cmd_names:
            assert cmd is not None, \
                    "the '%s' executable is not configured" % name
        elif not cmd:
            continue
        if spawn.find_executable(cmd[0]) is None:
            return cmd[0]


_is_android_emulator = None
def setswitchinterval(interval):
    # Setting a very low gil interval on the Android emulator causes python
    # to hang (issue #26939).
    minimum_interval = 1e-5
    if is_android and interval < minimum_interval:
        global _is_android_emulator
        if _is_android_emulator is None:
            import subprocess
            _is_android_emulator = (subprocess.check_output(
                               ['getprop', 'ro.kernel.qemu']).strip() == b'1')
        if _is_android_emulator:
            interval = minimum_interval
    return sys.setswitchinterval(interval)


@contextlib.contextmanager
def disable_faulthandler():
    import faulthandler

    # use sys.__stderr__ instead of sys.stderr, since regrtest replaces
    # sys.stderr with a StringIO which has no file descriptor when a test
    # is run with -W/--verbose3.
    fd = sys.__stderr__.fileno()

    is_enabled = faulthandler.is_enabled()
    try:
        faulthandler.disable()
        yield
    finally:
        if is_enabled:
            faulthandler.enable(file=fd, all_threads=True)


class SaveSignals:
    """
    Save and restore signal handlers.

    This class is only able to save/restore signal handlers registered
    by the Python signal module: see bpo-13285 for "external" signal
    handlers.
    """

    def __init__(self):
        import signal
        self.signal = signal
        self.signals = signal.valid_signals()
        # SIGKILL and SIGSTOP signals cannot be ignored nor caught
        for signame in ('SIGKILL', 'SIGSTOP'):
            try:
                signum = getattr(signal, signame)
            except AttributeError:
                continue
            self.signals.remove(signum)
        self.handlers = {}

    def save(self):
        for signum in self.signals:
            handler = self.signal.getsignal(signum)
            if handler is None:
                # getsignal() returns None if a signal handler was not
                # registered by the Python signal module,
                # and the handler is not SIG_DFL nor SIG_IGN.
                #
                # Ignore the signal: we cannot restore the handler.
                continue
            self.handlers[signum] = handler

    def restore(self):
        for signum, handler in self.handlers.items():
            self.signal.signal(signum, handler)


def with_pymalloc():
    import _testcapi
    return _testcapi.WITH_PYMALLOC


class _ALWAYS_EQ:
    """
    Object that is equal to anything.
    """
    def __eq__(self, other):
        return True
    def __ne__(self, other):
        return False

ALWAYS_EQ = _ALWAYS_EQ()

class _NEVER_EQ:
    """
    Object that is not equal to anything.
    """
    def __eq__(self, other):
        return False
    def __ne__(self, other):
        return True
    def __hash__(self):
        return 1

NEVER_EQ = _NEVER_EQ()

@functools.total_ordering
class _LARGEST:
    """
    Object that is greater than anything (except itself).
    """
    def __eq__(self, other):
        return isinstance(other, _LARGEST)
    def __lt__(self, other):
        return False

LARGEST = _LARGEST()

@functools.total_ordering
class _SMALLEST:
    """
    Object that is less than anything (except itself).
    """
    def __eq__(self, other):
        return isinstance(other, _SMALLEST)
    def __gt__(self, other):
        return False

SMALLEST = _SMALLEST()

def maybe_get_event_loop_policy():
    """Return the global event loop policy if one is set, else return None."""
    import asyncio.events
    return asyncio.events._event_loop_policy

# Helpers for testing hashing.
NHASHBITS = sys.hash_info.width # number of bits in hash() result
assert NHASHBITS in (32, 64)

# Return mean and sdev of number of collisions when tossing nballs balls
# uniformly at random into nbins bins.  By definition, the number of
# collisions is the number of balls minus the number of occupied bins at
# the end.
def collision_stats(nbins, nballs):
    n, k = nbins, nballs
    # prob a bin empty after k trials = (1 - 1/n)**k
    # mean # empty is then n * (1 - 1/n)**k
    # so mean # occupied is n - n * (1 - 1/n)**k
    # so collisions = k - (n - n*(1 - 1/n)**k)
    #
    # For the variance:
    # n*(n-1)*(1-2/n)**k + meanempty - meanempty**2 =
    # n*(n-1)*(1-2/n)**k + meanempty * (1 - meanempty)
    #
    # Massive cancellation occurs, and, e.g., for a 64-bit hash code
    # 1-1/2**64 rounds uselessly to 1.0.  Rather than make heroic (and
    # error-prone) efforts to rework the naive formulas to avoid those,
    # we use the `decimal` module to get plenty of extra precision.
    #
    # Note:  the exact values are straightforward to compute with
    # rationals, but in context that's unbearably slow, requiring
    # multi-million bit arithmetic.
    import decimal
    with decimal.localcontext() as ctx:
        bits = n.bit_length() * 2  # bits in n**2
        # At least that many bits will likely cancel out.
        # Use that many decimal digits instead.
        ctx.prec = max(bits, 30)
        dn = decimal.Decimal(n)
        p1empty = ((dn - 1) / dn) ** k
        meanempty = n * p1empty
        occupied = n - meanempty
        collisions = k - occupied
        var = dn*(dn-1)*((dn-2)/dn)**k + meanempty * (1 - meanempty)
        return float(collisions), float(var.sqrt())


class catch_unraisable_exception:
    """
    Context manager catching unraisable exception using sys.unraisablehook.

    Storing the exception value (cm.unraisable.exc_value) creates a reference
    cycle. The reference cycle is broken explicitly when the context manager
    exits.

    Storing the object (cm.unraisable.object) can resurrect it if it is set to
    an object which is being finalized. Exiting the context manager clears the
    stored object.

    Usage:

        with support.catch_unraisable_exception() as cm:
            # code creating an "unraisable exception"
            ...

            # check the unraisable exception: use cm.unraisable
            ...

        # cm.unraisable attribute no longer exists at this point
        # (to break a reference cycle)
    """

    def __init__(self):
        self.unraisable = None
        self._old_hook = None

    def _hook(self, unraisable):
        # Storing unraisable.object can resurrect an object which is being
        # finalized. Storing unraisable.exc_value creates a reference cycle.
        self.unraisable = unraisable

    def __enter__(self):
        self._old_hook = sys.unraisablehook
        sys.unraisablehook = self._hook
        return self

    def __exit__(self, *exc_info):
        sys.unraisablehook = self._old_hook
        del self.unraisable


def wait_process(pid, *, exitcode, timeout=None):
    """
    Wait until process pid completes and check that the process exit code is
    exitcode.

    Raise an AssertionError if the process exit code is not equal to exitcode.

    If the process runs longer than timeout seconds (SHORT_TIMEOUT by default),
    kill the process (if signal.SIGKILL is available) and raise an
    AssertionError. The timeout feature is not available on Windows.
    """
    if os.name != "nt":
        import signal

        if timeout is None:
            timeout = SHORT_TIMEOUT
        t0 = time.monotonic()
        sleep = 0.001
        max_sleep = 0.1
        while True:
            pid2, status = os.waitpid(pid, os.WNOHANG)
            if pid2 != 0:
                break
            # process is still running

            dt = time.monotonic() - t0
            if dt > SHORT_TIMEOUT:
                try:
                    os.kill(pid, signal.SIGKILL)
                    os.waitpid(pid, 0)
                except OSError:
                    # Ignore errors like ChildProcessError or PermissionError
                    pass

                raise AssertionError(f"process {pid} is still running "
                                     f"after {dt:.1f} seconds")

            sleep = min(sleep * 2, max_sleep)
            time.sleep(sleep)
    else:
        # Windows implementation
        pid2, status = os.waitpid(pid, 0)

    exitcode2 = os.waitstatus_to_exitcode(status)
    if exitcode2 != exitcode:
        raise AssertionError(f"process {pid} exited with code {exitcode2}, "
                             f"but exit code {exitcode} is expected")

    # sanity check: it should not fail in practice
    if pid2 != pid:
        raise AssertionError(f"pid {pid2} != pid {pid}")

def skip_if_broken_multiprocessing_synchronize():
    """
    Skip tests if the multiprocessing.synchronize module is missing, if there
    is no available semaphore implementation, or if creating a lock raises an
    OSError (on Linux only).
    """
    from .import_helper import import_module

    # Skip tests if the _multiprocessing extension is missing.
    import_module('_multiprocessing')

    # Skip tests if there is no available semaphore implementation:
    # multiprocessing.synchronize requires _multiprocessing.SemLock.
    synchronize = import_module('multiprocessing.synchronize')

    if sys.platform == "linux":
        try:
            # bpo-38377: On Linux, creating a semaphore fails with OSError
            # if the current user does not have the permission to create
            # a file in /dev/shm/ directory.
            synchronize.Lock(ctx=None)
        except OSError as exc:
            raise unittest.SkipTest(f"broken multiprocessing SemLock: {exc!r}")


@contextlib.contextmanager
def infinite_recursion(max_depth=75):
    original_depth = sys.getrecursionlimit()
    try:
        sys.setrecursionlimit(max_depth)
        yield
    finally:
        sys.setrecursionlimit(original_depth)


def check_disallow_instantiation(testcase, tp, *args, **kwds):
    """
    Check that given type cannot be instantiated using *args and **kwds.

    See bpo-43916: Add Py_TPFLAGS_DISALLOW_INSTANTIATION type flag.
    """
    mod = tp.__module__
    name = tp.__name__
    if mod != 'builtins':
        qualname = f"{mod}.{name}"
    else:
        qualname = f"{name}"
    msg = f"cannot create '{re.escape(qualname)}' instances"
    testcase.assertRaisesRegex(TypeError, msg, tp, *args, **kwds)


def ignore_deprecations_from(module: str, *, like: str) -> object:
    token = object()
    warnings.filterwarnings(
        "ignore",
        category=DeprecationWarning,
        module=module,
        message=like + fr"(?#support{id(token)})",
    )
    return token


def clear_ignored_deprecations(*tokens: object) -> None:
    if not tokens:
        raise ValueError("Provide token or tokens returned by ignore_deprecations_from")

    new_filters = []
    endswith = tuple(rf"(?#support{id(token)})" for token in tokens)
    for action, message, category, module, lineno in warnings.filters:
        if action == "ignore" and category is DeprecationWarning:
            if isinstance(message, re.Pattern):
                msg = message.pattern
            else:
                msg = message or ""
            if msg.endswith(endswith):
                continue
        new_filters.append((action, message, category, module, lineno))
    if warnings.filters != new_filters:
        warnings.filters[:] = new_filters
        warnings._filters_mutated()