"test" — Regression tests package for Python
********************************************

Note:

  The "test" package is meant for internal use by Python only. It is
  documented for the benefit of the core developers of Python. Any use
  of this package outside of Python’s standard library is discouraged
  as code mentioned here can change or be removed without notice
  between releases of Python.

======================================================================

The "test" package contains all regression tests for Python as well as
the modules "test.support" and "test.regrtest". "test.support" is used
to enhance your tests while "test.regrtest" drives the testing suite.

Each module in the "test" package whose name starts with "test_" is a
testing suite for a specific module or feature. All new tests should
be written using the "unittest" or "doctest" module.  Some older tests
are written using a “traditional” testing style that compares output
printed to "sys.stdout"; this style of test is considered deprecated.

See also:

  Module "unittest"
     Writing PyUnit regression tests.

  Module "doctest"
     Tests embedded in documentation strings.


Writing Unit Tests for the "test" package
=========================================

It is preferred that tests that use the "unittest" module follow a few
guidelines. One is to name the test module by starting it with "test_"
and end it with the name of the module being tested. The test methods
in the test module should start with "test_" and end with a
description of what the method is testing. This is needed so that the
methods are recognized by the test driver as test methods. Also, no
documentation string for the method should be included. A comment
(such as "# Tests function returns only True or False") should be used
to provide documentation for test methods. This is done because
documentation strings get printed out if they exist and thus what test
is being run is not stated.

A basic boilerplate is often used:

   import unittest
   from test import support

   class MyTestCase1(unittest.TestCase):

       # Only use setUp() and tearDown() if necessary

       def setUp(self):
           ... code to execute in preparation for tests ...

       def tearDown(self):
           ... code to execute to clean up after tests ...

       def test_feature_one(self):
           # Test feature one.
           ... testing code ...

       def test_feature_two(self):
           # Test feature two.
           ... testing code ...

       ... more test methods ...

   class MyTestCase2(unittest.TestCase):
       ... same structure as MyTestCase1 ...

   ... more test classes ...

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

This code pattern allows the testing suite to be run by
"test.regrtest", on its own as a script that supports the "unittest"
CLI, or via the "python -m unittest" CLI.

The goal for regression testing is to try to break code. This leads to
a few guidelines to be followed:

* The testing suite should exercise all classes, functions, and
  constants. This includes not just the external API that is to be
  presented to the outside world but also “private” code.

* Whitebox testing (examining the code being tested when the tests are
  being written) is preferred. Blackbox testing (testing only the
  published user interface) is not complete enough to make sure all
  boundary and edge cases are tested.

* Make sure all possible values are tested including invalid ones.
  This makes sure that not only all valid values are acceptable but
  also that improper values are handled correctly.

* Exhaust as many code paths as possible. Test where branching occurs
  and thus tailor input to make sure as many different paths through
  the code are taken.

* Add an explicit test for any bugs discovered for the tested code.
  This will make sure that the error does not crop up again if the
  code is changed in the future.

* Make sure to clean up after your tests (such as close and remove all
  temporary files).

* If a test is dependent on a specific condition of the operating
  system then verify the condition already exists before attempting
  the test.

* Import as few modules as possible and do it as soon as possible.
  This minimizes external dependencies of tests and also minimizes
  possible anomalous behavior from side-effects of importing a module.

* Try to maximize code reuse. On occasion, tests will vary by
  something as small as what type of input is used. Minimize code
  duplication by subclassing a basic test class with a class that
  specifies the input:

     class TestFuncAcceptsSequencesMixin:

         func = mySuperWhammyFunction

         def test_func(self):
             self.func(self.arg)

     class AcceptLists(TestFuncAcceptsSequencesMixin, unittest.TestCase):
         arg = [1, 2, 3]

     class AcceptStrings(TestFuncAcceptsSequencesMixin, unittest.TestCase):
         arg = 'abc'

     class AcceptTuples(TestFuncAcceptsSequencesMixin, unittest.TestCase):
         arg = (1, 2, 3)

  When using this pattern, remember that all classes that inherit from
  "unittest.TestCase" are run as tests.  The "Mixin" class in the
  example above does not have any data and so can’t be run by itself,
  thus it does not inherit from "unittest.TestCase".

See also:

  Test Driven Development
     A book by Kent Beck on writing tests before code.


Running tests using the command-line interface
==============================================

The "test" package can be run as a script to drive Python’s regression
test suite, thanks to the "-m" option: **python -m test**. Under the
hood, it uses "test.regrtest"; the call **python -m test.regrtest**
used in previous Python versions still works.  Running the script by
itself automatically starts running all regression tests in the "test"
package. It does this by finding all modules in the package whose name
starts with "test_", importing them, and executing the function
"test_main()" if present or loading the tests via
unittest.TestLoader.loadTestsFromModule if "test_main" does not exist.
The names of tests to execute may also be passed to the script.
Specifying a single regression test (**python -m test test_spam**)
will minimize output and only print whether the test passed or failed.

Running "test" directly allows what resources are available for tests
to use to be set. You do this by using the "-u" command-line option.
Specifying "all" as the value for the "-u" option enables all possible
resources: **python -m test -uall**. If all but one resource is
desired (a more common case), a comma-separated list of resources that
are not desired may be listed after "all". The command **python -m
test -uall,-audio,-largefile** will run "test" with all resources
except the "audio" and "largefile" resources. For a list of all
resources and more command-line options, run **python -m test -h**.

Some other ways to execute the regression tests depend on what
platform the tests are being executed on. On Unix, you can run **make
test** at the top-level directory where Python was built. On Windows,
executing **rt.bat** from your "PCbuild" directory will run all
regression tests.


"test.support" — Utilities for the Python test suite
****************************************************

The "test.support" module provides support for Python’s regression
test suite.

Note:

  "test.support" is not a public module.  It is documented here to
  help Python developers write tests.  The API of this module is
  subject to change without backwards compatibility concerns between
  releases.

This module defines the following exceptions:

exception test.support.TestFailed

   Exception to be raised when a test fails. This is deprecated in
   favor of "unittest"-based tests and "unittest.TestCase"’s assertion
   methods.

exception test.support.ResourceDenied

   Subclass of "unittest.SkipTest". Raised when a resource (such as a
   network connection) is not available. Raised by the "requires()"
   function.

The "test.support" module defines the following constants:

test.support.verbose

   "True" when verbose output is enabled. Should be checked when more
   detailed information is desired about a running test. *verbose* is
   set by "test.regrtest".

test.support.is_jython

   "True" if the running interpreter is Jython.

test.support.is_android

   "True" if the system is Android.

test.support.unix_shell

   Path for shell if not on Windows; otherwise "None".

test.support.FS_NONASCII

   A non-ASCII character encodable by "os.fsencode()".

test.support.TESTFN

   Set to a name that is safe to use as the name of a temporary file.
   Any temporary file that is created should be closed and unlinked
   (removed).

test.support.TESTFN_UNICODE

   Set to a non-ASCII name for a temporary file.

test.support.TESTFN_ENCODING

   Set to "sys.getfilesystemencoding()".

test.support.TESTFN_UNENCODABLE

   Set to a filename (str type) that should not be able to be encoded
   by file system encoding in strict mode.  It may be "None" if it’s
   not possible to generate such a filename.

test.support.TESTFN_UNDECODABLE

   Set to a filename (bytes type) that should not be able to be
   decoded by file system encoding in strict mode.  It may be "None"
   if it’s not possible to generate such a filename.

test.support.TESTFN_NONASCII

   Set to a filename containing the "FS_NONASCII" character.

test.support.LOOPBACK_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".

   Its default value is 5 seconds.

   See also "INTERNET_TIMEOUT".

test.support.INTERNET_TIMEOUT

   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()".

   Its default value is 1 minute.

   See also "LOOPBACK_TIMEOUT".

test.support.SHORT_TIMEOUT

   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.

   Its default value is 30 seconds.

test.support.LONG_TIMEOUT

   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.

   Its default value is 5 minutes.

   See also "LOOPBACK_TIMEOUT", "INTERNET_TIMEOUT" and
   "SHORT_TIMEOUT".

test.support.SAVEDCWD

   Set to "os.getcwd()".

test.support.PGO

   Set when tests can be skipped when they are not useful for PGO.

test.support.PIPE_MAX_SIZE

   A constant that is likely larger than the underlying OS pipe buffer
   size, to make writes blocking.

test.support.SOCK_MAX_SIZE

   A constant that is likely larger than the underlying OS socket
   buffer size, to make writes blocking.

test.support.TEST_SUPPORT_DIR

   Set to the top level directory that contains "test.support".

test.support.TEST_HOME_DIR

   Set to the top level directory for the test package.

test.support.TEST_DATA_DIR

   Set to the "data" directory within the test package.

test.support.MAX_Py_ssize_t

   Set to "sys.maxsize" for big memory tests.

test.support.max_memuse

   Set by "set_memlimit()" as the memory limit for big memory tests.
   Limited by "MAX_Py_ssize_t".

test.support.real_max_memuse

   Set by "set_memlimit()" as the memory limit for big memory tests.
   Not limited by "MAX_Py_ssize_t".

test.support.MISSING_C_DOCSTRINGS

   Return "True" if running on CPython, not on Windows, and
   configuration not set with "WITH_DOC_STRINGS".

test.support.HAVE_DOCSTRINGS

   Check for presence of docstrings.

test.support.TEST_HTTP_URL

   Define the URL of a dedicated HTTP server for the network tests.

test.support.ALWAYS_EQ

   Object that is equal to anything.  Used to test mixed type
   comparison.

test.support.NEVER_EQ

   Object that is not equal to anything (even to "ALWAYS_EQ"). Used to
   test mixed type comparison.

test.support.LARGEST

   Object that is greater than anything (except itself). Used to test
   mixed type comparison.

test.support.SMALLEST

   Object that is less than anything (except itself). Used to test
   mixed type comparison.

The "test.support" module defines the following functions:

test.support.forget(module_name)

   Remove the module named *module_name* from "sys.modules" and delete
   any byte-compiled files of the module.

test.support.unload(name)

   Delete *name* from "sys.modules".

test.support.unlink(filename)

   Call "os.unlink()" on *filename*.  On Windows platforms, this is
   wrapped with a wait loop that checks for the existence of the file.

test.support.rmdir(filename)

   Call "os.rmdir()" on *filename*.  On Windows platforms, this is
   wrapped with a wait loop that checks for the existence of the file.

test.support.rmtree(path)

   Call "shutil.rmtree()" on *path* or call "os.lstat()" and
   "os.rmdir()" to remove a path and its contents.  On Windows
   platforms, this is wrapped with a wait loop that checks for the
   existence of the files.

test.support.make_legacy_pyc(source)

   Move a **PEP 3147**/**PEP 488** pyc file to its legacy pyc location
   and return the file system path to the legacy pyc file.  The
   *source* value is the file system path to the source file.  It does
   not need to exist, however the PEP 3147/488 pyc file must exist.

test.support.is_resource_enabled(resource)

   Return "True" if *resource* is enabled and available. The list of
   available resources is only set when "test.regrtest" is executing
   the tests.

test.support.python_is_optimized()

   Return "True" if Python was not built with "-O0" or "-Og".

test.support.with_pymalloc()

   Return "_testcapi.WITH_PYMALLOC".

test.support.requires(resource, msg=None)

   Raise "ResourceDenied" if *resource* is not available. *msg* is the
   argument to "ResourceDenied" if it is raised. Always returns "True"
   if called by a function whose "__name__" is "'__main__'". Used when
   tests are executed by "test.regrtest".

test.support.system_must_validate_cert(f)

   Raise "unittest.SkipTest" on TLS certification validation failures.

test.support.sortdict(dict)

   Return a repr of *dict* with keys sorted.

test.support.findfile(filename, subdir=None)

   Return the path to the file named *filename*. If no match is found
   *filename* is returned. This does not equal a failure since it
   could be the path to the file.

   Setting *subdir* indicates a relative path to use to find the file
   rather than looking directly in the path directories.

test.support.create_empty_file(filename)

   Create an empty file with *filename*.  If it already exists,
   truncate it.

test.support.fd_count()

   Count the number of open file descriptors.

test.support.match_test(test)

   Match *test* to patterns set in "set_match_tests()".

test.support.set_match_tests(patterns)

   Define match test with regular expression *patterns*.

test.support.run_unittest(*classes)

   Execute "unittest.TestCase" subclasses passed to the function. The
   function scans the classes for methods starting with the prefix
   "test_" and executes the tests individually.

   It is also legal to pass strings as parameters; these should be
   keys in "sys.modules". Each associated module will be scanned by
   "unittest.TestLoader.loadTestsFromModule()". This is usually seen
   in the following "test_main()" function:

      def test_main():
          support.run_unittest(__name__)

   This will run all tests defined in the named module.

test.support.run_doctest(module, verbosity=None, optionflags=0)

   Run "doctest.testmod()" on the given *module*.  Return
   "(failure_count, test_count)".

   If *verbosity* is "None", "doctest.testmod()" is run with verbosity
   set to "verbose".  Otherwise, it is run with verbosity set to
   "None".  *optionflags* is passed as "optionflags" to
   "doctest.testmod()".

test.support.setswitchinterval(interval)

   Set the "sys.setswitchinterval()" to the given *interval*.  Defines
   a minimum interval for Android systems to prevent the system from
   hanging.

test.support.check_impl_detail(**guards)

   Use this check to guard CPython’s implementation-specific tests or
   to run them only on the implementations guarded by the arguments:

      check_impl_detail()               # Only on CPython (default).
      check_impl_detail(jython=True)    # Only on Jython.
      check_impl_detail(cpython=False)  # Everywhere except CPython.

test.support.check_warnings(*filters, quiet=True)

   A convenience wrapper for "warnings.catch_warnings()" that makes it
   easier to test that a warning was correctly raised.  It is
   approximately equivalent to calling
   "warnings.catch_warnings(record=True)" with
   "warnings.simplefilter()" set to "always" and with the option to
   automatically validate the results that are recorded.

   "check_warnings" accepts 2-tuples of the form "("message regexp",
   WarningCategory)" as positional arguments. If one or more *filters*
   are provided, or if the optional keyword argument *quiet* is
   "False", it checks to make sure the warnings are as expected:  each
   specified filter must match at least one of the warnings raised by
   the enclosed code or the test fails, and if any warnings are raised
   that do not match any of the specified filters the test fails.  To
   disable the first of these checks, set *quiet* to "True".

   If no arguments are specified, it defaults to:

      check_warnings(("", Warning), quiet=True)

   In this case all warnings are caught and no errors are raised.

   On entry to the context manager, a "WarningRecorder" instance is
   returned. The underlying warnings list from "catch_warnings()" is
   available via the recorder object’s "warnings" attribute.  As a
   convenience, the attributes of the object representing the most
   recent warning can also be accessed directly through the recorder
   object (see example below).  If no warning has been raised, then
   any of the attributes that would otherwise be expected on an object
   representing a warning will return "None".

   The recorder object also has a "reset()" method, which clears the
   warnings list.

   The context manager is designed to be used like this:

      with check_warnings(("assertion is always true", SyntaxWarning),
                          ("", UserWarning)):
          exec('assert(False, "Hey!")')
          warnings.warn(UserWarning("Hide me!"))

   In this case if either warning was not raised, or some other
   warning was raised, "check_warnings()" would raise an error.

   When a test needs to look more deeply into the warnings, rather
   than just checking whether or not they occurred, code like this can
   be used:

      with check_warnings(quiet=True) as w:
          warnings.warn("foo")
          assert str(w.args[0]) == "foo"
          warnings.warn("bar")
          assert str(w.args[0]) == "bar"
          assert str(w.warnings[0].args[0]) == "foo"
          assert str(w.warnings[1].args[0]) == "bar"
          w.reset()
          assert len(w.warnings) == 0

   Here all warnings will be caught, and the test code tests the
   captured warnings directly.

   Changed in version 3.2: New optional arguments *filters* and
   *quiet*.

test.support.check_no_resource_warning(testcase)

   Context manager to check that no "ResourceWarning" was raised.  You
   must remove the object which may emit "ResourceWarning" before the
   end of the context manager.

test.support.set_memlimit(limit)

   Set the values for "max_memuse" and "real_max_memuse" for big
   memory tests.

test.support.record_original_stdout(stdout)

   Store the value from *stdout*.  It is meant to hold the stdout at
   the time the regrtest began.

test.support.get_original_stdout()

   Return the original stdout set by "record_original_stdout()" or
   "sys.stdout" if it’s not set.

test.support.args_from_interpreter_flags()

   Return a list of command line arguments reproducing the current
   settings in "sys.flags" and "sys.warnoptions".

test.support.optim_args_from_interpreter_flags()

   Return a list of command line arguments reproducing the current
   optimization settings in "sys.flags".

test.support.captured_stdin()
test.support.captured_stdout()
test.support.captured_stderr()

   A context managers that temporarily replaces the named stream with
   "io.StringIO" object.

   Example use with output streams:

      with captured_stdout() as stdout, captured_stderr() as stderr:
          print("hello")
          print("error", file=sys.stderr)
      assert stdout.getvalue() == "hello\n"
      assert stderr.getvalue() == "error\n"

   Example use with input stream:

      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")

test.support.temp_dir(path=None, quiet=False)

   A context manager that creates a temporary directory at *path* and
   yields the directory.

   If *path* is "None", the temporary directory is created using
   "tempfile.mkdtemp()".  If *quiet* is "False", the context manager
   raises an exception on error.  Otherwise, if *path* is specified
   and cannot be created, only a warning is issued.

test.support.change_cwd(path, quiet=False)

   A context manager that temporarily changes the current working
   directory to *path* and yields the directory.

   If *quiet* is "False", the context manager raises an exception on
   error.  Otherwise, it issues only a warning and keeps the current
   working directory the same.

test.support.temp_cwd(name='tempcwd', quiet=False)

   A context manager that temporarily creates a new directory and
   changes the current working directory (CWD).

   The context manager creates a temporary directory in the current
   directory with name *name* before temporarily changing the current
   working directory.  If *name* is "None", the temporary directory is
   created using "tempfile.mkdtemp()".

   If *quiet* is "False" and it is not possible to create or change
   the CWD, an error is raised.  Otherwise, only a warning is raised
   and the original CWD is used.

test.support.temp_umask(umask)

   A context manager that temporarily sets the process umask.

test.support.disable_faulthandler()

   A context manager that replaces "sys.stderr" with "sys.__stderr__".

test.support.gc_collect()

   Force as many objects as possible to be collected.  This is needed
   because timely deallocation is not guaranteed by the garbage
   collector.  This means that "__del__" methods may be called later
   than expected and weakrefs may remain alive for longer than
   expected.

test.support.disable_gc()

   A context manager that disables the garbage collector upon entry
   and reenables it upon exit.

test.support.swap_attr(obj, attr, new_val)

   Context manager to 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.

test.support.swap_item(obj, attr, new_val)

   Context manager to 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.

test.support.print_warning(msg)

   Print a warning into "sys.__stderr__". Format the message as:
   "f"Warning -- {msg}"". If *msg* is made of multiple lines, add
   ""Warning -- "" prefix to each line.

   New in version 3.9.

test.support.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 and raise an "AssertionError". The
   timeout feature is not available on Windows.

   New in version 3.9.

test.support.wait_threads_exit(timeout=60.0)

   Context manager to wait until all threads created in the "with"
   statement exit.

test.support.start_threads(threads, unlock=None)

   Context manager to start *threads*.  It attempts to join the
   threads upon exit.

test.support.calcobjsize(fmt)

   Return "struct.calcsize()" for "nP{fmt}0n" or, if
   "gettotalrefcount" exists, "2PnP{fmt}0P".

test.support.calcvobjsize(fmt)

   Return "struct.calcsize()" for "nPn{fmt}0n" or, if
   "gettotalrefcount" exists, "2PnPn{fmt}0P".

test.support.checksizeof(test, o, size)

   For testcase *test*, assert that the "sys.getsizeof" for *o* plus
   the GC header size equals *size*.

test.support.can_symlink()

   Return "True" if the OS supports symbolic links, "False" otherwise.

test.support.can_xattr()

   Return "True" if the OS supports xattr, "False" otherwise.

@test.support.skip_unless_symlink

   A decorator for running tests that require support for symbolic
   links.

@test.support.skip_unless_xattr

   A decorator for running tests that require support for xattr.

@test.support.anticipate_failure(condition)

   A decorator to conditionally mark tests with
   "unittest.expectedFailure()". Any use of this decorator should have
   an associated comment identifying the relevant tracker issue.

@test.support.run_with_locale(catstr, *locales)

   A decorator for running a function in a different locale, correctly
   resetting it after it has finished.  *catstr* is the locale
   category as a string (for example ""LC_ALL"").  The *locales*
   passed will be tried sequentially, and the first valid locale will
   be used.

@test.support.run_with_tz(tz)

   A decorator for running a function in a specific timezone,
   correctly resetting it after it has finished.

@test.support.requires_freebsd_version(*min_version)

   Decorator for the minimum version when running test on FreeBSD.  If
   the FreeBSD version is less than the minimum, raise
   "unittest.SkipTest".

@test.support.requires_linux_version(*min_version)

   Decorator for the minimum version when running test on Linux.  If
   the Linux version is less than the minimum, raise
   "unittest.SkipTest".

@test.support.requires_mac_version(*min_version)

   Decorator for the minimum version when running test on macOS.  If
   the macOS version is less than the minimum, raise
   "unittest.SkipTest".

@test.support.requires_IEEE_754

   Decorator for skipping tests on non-IEEE 754 platforms.

@test.support.requires_zlib

   Decorator for skipping tests if "zlib" doesn’t exist.

@test.support.requires_gzip

   Decorator for skipping tests if "gzip" doesn’t exist.

@test.support.requires_bz2

   Decorator for skipping tests if "bz2" doesn’t exist.

@test.support.requires_lzma

   Decorator for skipping tests if "lzma" doesn’t exist.

@test.support.requires_resource(resource)

   Decorator for skipping tests if *resource* is not available.

@test.support.requires_docstrings

   Decorator for only running the test if "HAVE_DOCSTRINGS".

@test.support.cpython_only(test)

   Decorator for tests only applicable to CPython.

@test.support.impl_detail(msg=None, **guards)

   Decorator for invoking "check_impl_detail()" on *guards*.  If that
   returns "False", then uses *msg* as the reason for skipping the
   test.

@test.support.no_tracing(func)

   Decorator to temporarily turn off tracing for the duration of the
   test.

@test.support.refcount_test(test)

   Decorator for tests which involve reference counting.  The
   decorator does not run the test if it is not run by CPython.  Any
   trace function is unset for the duration of the test to prevent
   unexpected refcounts caused by the trace function.

@test.support.reap_threads(func)

   Decorator to ensure the threads are cleaned up even if the test
   fails.

@test.support.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.

@test.support.bigaddrspacetest(f)

   Decorator for tests that fill the address space.  *f* is the
   function to wrap.

test.support.make_bad_fd()

   Create an invalid file descriptor by opening and closing a
   temporary file, and returning its descriptor.

test.support.check_syntax_error(testcase, statement, errtext='', *, lineno=None, offset=None)

   Test for syntax errors in *statement* by attempting to compile
   *statement*. *testcase* is the "unittest" instance for the test.
   *errtext* is the regular expression which should match the string
   representation of the raised "SyntaxError".  If *lineno* is not
   "None", compares to the line of the exception.  If *offset* is not
   "None", compares to the offset of the exception.

test.support.check_syntax_warning(testcase, statement, errtext='', *, lineno=1, offset=None)

   Test for syntax warning in *statement* by attempting to compile
   *statement*. Test also that the "SyntaxWarning" is emitted only
   once, and that it will be converted to a "SyntaxError" when turned
   into error. *testcase* is the "unittest" instance for the test.
   *errtext* is the regular expression which should match the string
   representation of the emitted "SyntaxWarning" and raised
   "SyntaxError".  If *lineno* is not "None", compares to the line of
   the warning and exception. If *offset* is not "None", compares to
   the offset of the exception.

   New in version 3.8.

test.support.open_urlresource(url, *args, **kw)

   Open *url*.  If open fails, raises "TestFailed".

test.support.import_module(name, deprecated=False, *, required_on())

   This function imports and returns the named module. Unlike a normal
   import, this function raises "unittest.SkipTest" if the module
   cannot be imported.

   Module and package deprecation messages are suppressed during this
   import if *deprecated* is "True".  If a module is required on a
   platform but optional for others, set *required_on* to an iterable
   of platform prefixes which will be compared against "sys.platform".

   New in version 3.1.

test.support.import_fresh_module(name, fresh=(), blocked=(), deprecated=False)

   This function imports and returns a fresh copy of the named Python
   module by removing the named module from "sys.modules" before doing
   the import. Note that unlike "reload()", the original module is not
   affected by this operation.

   *fresh* is an iterable of additional module names that are also
   removed from the "sys.modules" cache before doing the import.

   *blocked* is an iterable of module names that are replaced with
   "None" in the module cache during the import to ensure that
   attempts to import them raise "ImportError".

   The named module and any modules named in the *fresh* and *blocked*
   parameters are saved before starting the import and then reinserted
   into "sys.modules" when the fresh import is complete.

   Module and package deprecation messages are suppressed during this
   import if *deprecated* is "True".

   This function will raise "ImportError" if the named module cannot
   be imported.

   Example use:

      # Get copies of the warnings module for testing without affecting the
      # version being used by the rest of the test suite. One copy uses the
      # C implementation, the other is forced to use the pure Python fallback
      # implementation
      py_warnings = import_fresh_module('warnings', blocked=['_warnings'])
      c_warnings = import_fresh_module('warnings', fresh=['_warnings'])

   New in version 3.1.

test.support.modules_setup()

   Return a copy of "sys.modules".

test.support.modules_cleanup(oldmodules)

   Remove modules except for *oldmodules* and "encodings" in order to
   preserve internal cache.

test.support.threading_setup()

   Return current thread count and copy of dangling threads.

test.support.threading_cleanup(*original_values)

   Cleanup up threads not specified in *original_values*.  Designed to
   emit a warning if a test leaves running threads in the background.

test.support.join_thread(thread, timeout=30.0)

   Join a *thread* within *timeout*.  Raise an "AssertionError" if
   thread is still alive after *timeout* seconds.

test.support.reap_children()

   Use this 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.

test.support.get_attribute(obj, name)

   Get an attribute, raising "unittest.SkipTest" if "AttributeError"
   is raised.

test.support.catch_threading_exception()

   Context manager catching "threading.Thread" exception using
   "threading.excepthook()".

   Attributes set when an exception is caught:

   * "exc_type"

   * "exc_value"

   * "exc_traceback"

   * "thread"

   See "threading.excepthook()" documentation.

   These attributes are deleted at the context manager exit.

   Usage:

      with support.catch_threading_exception() as cm:
          # code spawning a thread which raises an exception
          ...

          # check the thread exception, use cm attributes:
          # exc_type, exc_value, exc_traceback, thread
          ...

      # exc_type, exc_value, exc_traceback, thread attributes of cm no longer
      # exists at this point
      # (to avoid reference cycles)

   New in version 3.8.

test.support.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)

   New in version 3.8.

test.support.load_package_tests(pkg_dir, loader, standard_tests, pattern)

   Generic implementation of the "unittest" "load_tests" protocol for
   use in test packages.  *pkg_dir* is the root directory of the
   package; *loader*, *standard_tests*, and *pattern* are the
   arguments expected by "load_tests".  In simple cases, the test
   package’s "__init__.py" can be the following:

      import os
      from test.support import load_package_tests

      def load_tests(*args):
          return load_package_tests(os.path.dirname(__file__), *args)

test.support.fs_is_case_insensitive(directory)

   Return "True" if the file system for *directory* is case-
   insensitive.

test.support.detect_api_mismatch(ref_api, other_api, *, ignore=())

   Returns the set of attributes, functions or methods of *ref_api*
   not found on *other_api*, except for a defined list of items to be
   ignored in this check specified in *ignore*.

   By default this skips private attributes beginning with ‘_’ but
   includes all magic methods, i.e. those starting and ending in ‘__’.

   New in version 3.5.

test.support.patch(test_instance, object_to_patch, attr_name, new_value)

   Override *object_to_patch.attr_name* with *new_value*.  Also add
   cleanup procedure to *test_instance* to restore *object_to_patch*
   for *attr_name*.  The *attr_name* should be a valid attribute for
   *object_to_patch*.

test.support.run_in_subinterp(code)

   Run *code* in subinterpreter.  Raise "unittest.SkipTest" if
   "tracemalloc" is enabled.

test.support.check_free_after_iterating(test, iter, cls, args=())

   Assert that *iter* is deallocated after iterating.

test.support.missing_compiler_executable(cmd_names=[])

   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.

test.support.check__all__(test_case, module, name_of_module=None, extra=(), blacklist=())

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

   Example use:

      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'}
              blacklist = {'baz'}  # Undocumented name.
              # bar imports part of its API from _bar.
              support.check__all__(self, bar, ('bar', '_bar'),
                                   extra=extra, blacklist=blacklist)

   New in version 3.6.

The "test.support" module defines the following classes:

class test.support.TransientResource(exc, **kwargs)

   Instances are a context manager that raises "ResourceDenied" if the
   specified exception type is raised.  Any keyword arguments are
   treated as attribute/value pairs to be compared against any
   exception raised within the "with" statement.  Only if all pairs
   match properly against attributes on the exception is
   "ResourceDenied" raised.

class test.support.EnvironmentVarGuard

   Class used to temporarily set or unset environment variables.
   Instances can be used as a context manager and have a complete
   dictionary interface for querying/modifying the underlying
   "os.environ". After exit from the context manager all changes to
   environment variables done through this instance will be rolled
   back.

   Changed in version 3.1: Added dictionary interface.

EnvironmentVarGuard.set(envvar, value)

   Temporarily set the environment variable "envvar" to the value of
   "value".

EnvironmentVarGuard.unset(envvar)

   Temporarily unset the environment variable "envvar".

class test.support.SuppressCrashReport

   A context manager used to try to prevent crash dialog popups on
   tests that are expected to crash a subprocess.

   On Windows, it disables Windows Error Reporting dialogs using
   SetErrorMode.

   On UNIX, "resource.setrlimit()" is used to set
   "resource.RLIMIT_CORE"’s soft limit to 0 to prevent coredump file
   creation.

   On both platforms, the old value is restored by "__exit__()".

class test.support.CleanImport(*module_names)

   A context manager to force import to return a new module reference.
   This is useful for testing module-level behaviors, such as the
   emission of a DeprecationWarning on import.  Example usage:

      with CleanImport('foo'):
          importlib.import_module('foo')  # New reference.

class test.support.DirsOnSysPath(*paths)

   A context manager to temporarily add directories to sys.path.

   This makes a copy of "sys.path", appends any directories given as
   positional arguments, then reverts "sys.path" to the copied
   settings when the context ends.

   Note that *all* "sys.path" modifications in the body of the context
   manager, including replacement of the object, will be reverted at
   the end of the block.

class test.support.SaveSignals

   Class to save and restore signal handlers registered by the Python
   signal handler.

class test.support.Matcher

   matches(self, d, **kwargs)

      Try to match a single dict with the supplied arguments.

   match_value(self, k, dv, v)

      Try to match a single stored value (*dv*) with a supplied value
      (*v*).

class test.support.WarningsRecorder

   Class used to record warnings for unit tests. See documentation of
   "check_warnings()" above for more details.

class test.support.BasicTestRunner

   run(test)

      Run *test* and return the result.

class test.support.FakePath(path)

   Simple *path-like object*.  It implements the "__fspath__()" method
   which just returns the *path* argument.  If *path* is an exception,
   it will be raised in "__fspath__()".


"test.support.socket_helper" — Utilities for socket tests
*********************************************************

The "test.support.socket_helper" module provides support for socket
tests.

New in version 3.9.

test.support.socket_helper.IPV6_ENABLED

   Set to "True" if IPv6 is enabled on this host, "False" otherwise.

test.support.socket_helper.find_unused_port(family=socket.AF_INET, socktype=socket.SOCK_STREAM)

   Returns an unused port that should be suitable for binding.  This
   is achieved by creating a temporary socket with the same family and
   type as the "sock" parameter (default is "AF_INET", "SOCK_STREAM"),
   and binding it to the specified host address (defaults to
   "0.0.0.0") with the port set to 0, eliciting an unused ephemeral
   port from the OS. The temporary socket is then closed and deleted,
   and the ephemeral port is returned.

   Either this method or "bind_port()" should be used for any tests
   where a server socket needs to be bound to a particular port for
   the duration of the test. Which one to use depends on whether the
   calling code is creating a Python socket, or if an unused port
   needs to be provided in a constructor or passed to an external
   program (i.e. the "-accept" argument to openssl’s s_server mode).
   Always prefer "bind_port()" over "find_unused_port()" where
   possible.  Using a hard coded port is discouraged since it can make
   multiple instances of the test impossible to run simultaneously,
   which is a problem for buildbots.

test.support.socket_helper.bind_port(sock, host=HOST)

   Bind the socket to a free port and return the port number.  Relies
   on ephemeral ports in order to ensure we are using an unbound port.
   This is important as many tests may be running simultaneously,
   especially in a buildbot environment.  This method raises an
   exception if the "sock.family" is "AF_INET" and "sock.type" is
   "SOCK_STREAM", and the socket has "SO_REUSEADDR" or "SO_REUSEPORT"
   set on it. Tests should never set these socket options for TCP/IP
   sockets. The only case for setting these options is testing
   multicasting via multiple UDP sockets.

   Additionally, if the "SO_EXCLUSIVEADDRUSE" socket option is
   available (i.e. on Windows), it will be set on the socket.  This
   will prevent anyone else from binding to our host/port for the
   duration of the test.

test.support.socket_helper.bind_unix_socket(sock, addr)

   Bind a unix socket, raising "unittest.SkipTest" if
   "PermissionError" is raised.

@test.support.socket_helper.skip_unless_bind_unix_socket

   A decorator for running tests that require a functional "bind()"
   for Unix sockets.

test.support.socket_helper.transient_internet(resource_name, *, timeout=30.0, errnos=())

   A context manager that raises "ResourceDenied" when various issues
   with the internet connection manifest themselves as exceptions.


"test.support.script_helper" — Utilities for the Python execution tests
***********************************************************************

The "test.support.script_helper" module provides support for Python’s
script execution tests.

test.support.script_helper.interpreter_requires_environment()

   Return "True" if "sys.executable interpreter" requires environment
   variables in order to be able to run at all.

   This is designed to be used with "@unittest.skipIf()" to annotate
   tests that need to use an "assert_python*()" function to launch an
   isolated mode ("-I") or no environment mode ("-E") sub-interpreter
   process.

   A normal build & test does not run into this situation but it can
   happen when trying to run the standard library test suite from an
   interpreter that doesn’t have an obvious home with Python’s current
   home finding logic.

   Setting "PYTHONHOME" is one way to get most of the testsuite to run
   in that situation.  "PYTHONPATH" or "PYTHONUSERSITE" are other
   common environment variables that might impact whether or not the
   interpreter can start.

test.support.script_helper.run_python_until_end(*args, **env_vars)

   Set up the environment based on *env_vars* for running the
   interpreter in a subprocess.  The values can include "__isolated",
   "__cleanenv", "__cwd", and "TERM".

   Changed in version 3.9: The function no longer strips whitespaces
   from *stderr*.

test.support.script_helper.assert_python_ok(*args, **env_vars)

   Assert that running the interpreter with *args* and optional
   environment variables *env_vars* succeeds ("rc == 0") and return a
   "(return code, stdout, stderr)" tuple.

   If the "__cleanenv" keyword is set, *env_vars* is used as a fresh
   environment.

   Python is started in isolated mode (command line option "-I"),
   except if the "__isolated" keyword is set to "False".

   Changed in version 3.9: The function no longer strips whitespaces
   from *stderr*.

test.support.script_helper.assert_python_failure(*args, **env_vars)

   Assert that running the interpreter with *args* and optional
   environment variables *env_vars* fails ("rc != 0") and return a
   "(return code, stdout, stderr)" tuple.

   See "assert_python_ok()" for more options.

   Changed in version 3.9: The function no longer strips whitespaces
   from *stderr*.

test.support.script_helper.spawn_python(*args, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, **kw)

   Run a Python subprocess with the given arguments.

   *kw* is extra keyword args to pass to "subprocess.Popen()". Returns
   a "subprocess.Popen" object.

test.support.script_helper.kill_python(p)

   Run the given "subprocess.Popen" process until completion and
   return stdout.

test.support.script_helper.make_script(script_dir, script_basename, source, omit_suffix=False)

   Create script containing *source* in path *script_dir* and
   *script_basename*. If *omit_suffix* is "False", append ".py" to the
   name.  Return the full script path.

test.support.script_helper.make_zip_script(zip_dir, zip_basename, script_name, name_in_zip=None)

   Create zip file at *zip_dir* and *zip_basename* with extension
   "zip" which contains the files in *script_name*. *name_in_zip* is
   the archive name. Return a tuple containing "(full path, full path
   of archive name)".

test.support.script_helper.make_pkg(pkg_dir, init_source='')

   Create a directory named *pkg_dir* containing an "__init__" file
   with *init_source* as its contents.

test.support.script_helper.make_zip_pkg(zip_dir, zip_basename, pkg_name, script_basename, source, depth=1, compiled=False)

   Create a zip package directory with a path of *zip_dir* and
   *zip_basename* containing an empty "__init__" file and a file
   *script_basename* containing the *source*.  If *compiled* is
   "True", both source files will be compiled and added to the zip
   package.  Return a tuple of the full zip path and the archive name
   for the zip file.


"test.support.bytecode_helper" — Support tools for testing correct bytecode generation
**************************************************************************************

The "test.support.bytecode_helper" module provides support for testing
and inspecting bytecode generation.

New in version 3.9.

The module defines the following class:

class test.support.bytecode_helper.BytecodeTestCase(unittest.TestCase)

   This class has custom assertion methods for inspecting bytecode.

BytecodeTestCase.get_disassembly_as_string(co)

   Return the disassembly of *co* as string.

BytecodeTestCase.assertInBytecode(x, opname, argval=_UNSPECIFIED)

   Return instr if *opname* is found, otherwise throws
   "AssertionError".

BytecodeTestCase.assertNotInBytecode(x, opname, argval=_UNSPECIFIED)

   Throws "AssertionError" if *opname* is found.
