:mod:`test` --- Regression tests package for Python

.. module:: test
 :synopsis: Regression tests package containing the testing suite for Python.

.. sectionauthor:: Brett Cannon <brett@python.org>

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

Each module in the :mod:`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 :mod:`unittest` or :mod:`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.

.. seealso::

 Module :mod:`unittest`
 Writing PyUnit regression tests.

 Module :mod:`doctest`
 Tests embedded in documentation strings.

Writing Unit Tests for the :mod:`test` package

It is preferred that tests that use the :mod:`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 :mod:`test.regrtest`, on its own as a script that supports the :mod:`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 :class:`unittest.TestCase` are run as tests. The :class:`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 :class:`unittest.TestCase`.

.. seealso::

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

Running tests using the command-line interface

The :mod:`test` package can be run as a script to drive Python's regression test suite, thanks to the :option:`-m` option: :program:`python -m test`. Under the hood, it uses :mod:`test.regrtest`; the call :program:`python -m test.regrtest` used in previous Python versions still works. Running the script by itself automatically starts running all regression tests in the :mod:`test` package. It does this by finding all modules in the package whose name starts with test_, importing them, and executing the function :func:`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 (:program:`python -m test test_spam`) will minimize output and only print whether the test passed or failed.

Running :mod:`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: :program:`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 :program:`python -m test -uall,-audio,-largefile` will run :mod:`test` with all resources except the audio and largefile resources. For a list of all resources and more command-line options, run :program:`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 :program:`make test` at the top-level directory where Python was built. On Windows, executing :program:`rt.bat` from your :file:`PCbuild` directory will run all regression tests.

:mod:`test.support` --- Utilities for the Python test suite

.. module:: test.support
 :synopsis: Support for Python's regression test suite.

The :mod:`test.support` module provides support for Python's regression test suite.

This module defines the following exceptions:

.. exception:: TestFailed

 Exception to be raised when a test fails. This is deprecated in favor of
 :mod:`unittest`\ -based tests and :class:`unittest.TestCase`'s assertion
 methods.

.. exception:: ResourceDenied

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

The :mod:`test.support` module defines the following constants:

.. data:: verbose

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

.. data:: is_jython

 ``True`` if the running interpreter is Jython.

.. data:: is_android

 ``True`` if the system is Android.

.. data:: unix_shell

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

.. data:: FS_NONASCII

 A non-ASCII character encodable by :func:`os.fsencode`.

.. data:: 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).

.. data:: TESTFN_UNICODE

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

.. data:: TESTFN_ENCODING

 Set to :func:`sys.getfilesystemencoding`.

.. data:: 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.

.. data:: 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.

.. data:: TESTFN_NONASCII

 Set to a filename containing the :data:`FS_NONASCII` character.

.. data:: IPV6_ENABLED

 Set to ``True`` if IPV6 is enabled on this host, ``False`` otherwise.

.. data:: SAVEDCWD

 Set to :func:`os.getcwd`.

.. data:: PGO

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

.. data:: PIPE_MAX_SIZE

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

.. data:: SOCK_MAX_SIZE

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

.. data:: TEST_SUPPORT_DIR

 Set to the top level directory that contains :mod:`test.support`.

.. data:: TEST_HOME_DIR

 Set to the top level directory for the test package.

.. data:: TEST_DATA_DIR

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

.. data:: MAX_Py_ssize_t

 Set to :data:`sys.maxsize` for big memory tests.

.. data:: max_memuse

 Set by :func:`set_memlimit` as the memory limit for big memory tests.
 Limited by :data:`MAX_Py_ssize_t`.

.. data:: real_max_memuse

 Set by :func:`set_memlimit` as the memory limit for big memory tests. Not
 limited by :data:`MAX_Py_ssize_t`.

.. data:: MISSING_C_DOCSTRINGS

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

.. data:: HAVE_DOCSTRINGS

 Check for presence of docstrings.

.. data:: TEST_HTTP_URL

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

.. data:: ALWAYS_EQ

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

.. data:: LARGEST

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

.. data:: SMALLEST

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

The :mod:`test.support` module defines the following functions:

.. function:: forget(module_name)

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

.. function:: unload(name)

 Delete *name* from ``sys.modules``.

.. function:: unlink(filename)

 Call :func:`os.unlink` on *filename*. On Windows platforms, this is
 wrapped with a wait loop that checks for the existence fo the file.

.. function:: rmdir(filename)

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

.. function:: rmtree(path)

 Call :func:`shutil.rmtree` on *path* or call :func:`os.lstat` and
 :func:`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.

.. function:: 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.

.. function:: is_resource_enabled(resource)

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

.. function:: python_is_optimized()

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

.. function:: with_pymalloc()

 Return :data:`_testcapi.WITH_PYMALLOC`.

.. function:: requires(resource, msg=None)

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

.. function:: system_must_validate_cert(f)

 Raise :exc:`unittest.SkipTest` on TLS certification validation failures.

.. function:: sortdict(dict)

 Return a repr of *dict* with keys sorted.

.. function:: 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.

.. function:: create_empty_file(filename)

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

.. function:: fd_count()

 Count the number of open file descriptors.

.. function:: match_test(test)

 Match *test* to patterns set in :func:`set_match_tests`.

.. function:: set_match_tests(patterns)

 Define match test with regular expression *patterns*.

.. function:: run_unittest(\*classes)

 Execute :class:`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 :func:`test_main` function::

 def test_main():
 support.run_unittest(__name__)

 This will run all tests defined in the named module.

.. function:: run_doctest(module, verbosity=None, optionflags=0)

 Run :func:`doctest.testmod` on the given *module*. Return
 ``(failure_count, test_count)``.

 If *verbosity* is ``None``, :func:`doctest.testmod` is run with verbosity
 set to :data:`verbose`. Otherwise, it is run with verbosity set to
 ``None``. *optionflags* is passed as ``optionflags`` to
 :func:`doctest.testmod`.

.. function:: setswitchinterval(interval)

 Set the :func:`sys.setswitchinterval` to the given *interval*. Defines
 a minimum interval for Android systems to prevent the system from hanging.

.. function:: 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.

.. function:: check_warnings(\*filters, quiet=True)

 A convenience wrapper for :func:`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
 :meth:`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 :class:`WarningRecorder` instance is
 returned. The underlying warnings list from
 :func:`~warnings.catch_warnings` is available via the recorder object's
 :attr:`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 :meth:`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, :func:`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.

 .. versionchanged:: 3.2
 New optional arguments *filters* and *quiet*.

.. function:: check_no_resource_warning(testcase)

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

.. function:: set_memlimit(limit)

 Set the values for :data:`max_memuse` and :data:`real_max_memuse` for big
 memory tests.

.. function:: record_original_stdout(stdout)

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

.. function:: get_original_stdout

 Return the original stdout set by :func:`record_original_stdout` or
 ``sys.stdout`` if it's not set.

.. function:: strip_python_strerr(stderr)

 Strip the *stderr* of a Python process from potential debug output
 emitted by the interpreter. This will typically be run on the result of
 :meth:`subprocess.Popen.communicate`.

.. function:: args_from_interpreter_flags()

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

.. function:: optim_args_from_interpreter_flags()

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

.. function:: captured_stdin()
 captured_stdout()
 captured_stderr()

 A context managers that temporarily replaces the named stream with
 :class:`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")

.. function:: 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
 :func:`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.

.. function:: 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.

.. function:: 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 :func:`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.

.. function:: temp_umask(umask)

 A context manager that temporarily sets the process umask.

.. function:: transient_internet(resource_name, *, timeout=30.0, errnos=())

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

.. function:: disable_faulthandler()

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

.. function:: 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.

.. function:: disable_gc()

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

.. function:: 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.

.. function:: 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.

.. function:: wait_threads_exit(timeout=60.0)

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

.. function:: start_threads(threads, unlock=None)

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

.. function:: calcobjsize(fmt)

 Return :func:`struct.calcsize` for ``nP{fmt}0n`` or, if ``gettotalrefcount``
 exists, ``2PnP{fmt}0P``.

.. function:: calcvobjsize(fmt)

 Return :func:`struct.calcsize` for ``nPn{fmt}0n`` or, if ``gettotalrefcount``
 exists, ``2PnPn{fmt}0P``.

.. function:: checksizeof(test, o, size)

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

.. function:: can_symlink()

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

.. function:: can_xattr()

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

.. decorator:: skip_unless_symlink

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

.. decorator:: skip_unless_xattr

 A decorator for running tests that require support for xattr.

.. decorator:: skip_unless_bind_unix_socket

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

.. decorator:: anticipate_failure(condition)

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

.. decorator:: 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.

.. decorator:: run_with_tz(tz)

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

.. decorator:: 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 :exc:`unittest.SkipTest`.

.. decorator:: 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 :exc:`unittest.SkipTest`.

.. decorator:: requires_mac_version(*min_version)

 Decorator for the minimum version when running test on Mac OS X. If the
 MAC OS X version is less than the minimum, raise :exc:`unittest.SkipTest`.

.. decorator:: requires_IEEE_754

 Decorator for skipping tests on non-IEEE 754 platforms.

.. decorator:: requires_zlib

 Decorator for skipping tests if :mod:`zlib` doesn't exist.

.. decorator:: requires_gzip

 Decorator for skipping tests if :mod:`gzip` doesn't exist.

.. decorator:: requires_bz2

 Decorator for skipping tests if :mod:`bz2` doesn't exist.

.. decorator:: requires_lzma

 Decorator for skipping tests if :mod:`lzma` doesn't exist.

.. decorator:: requires_resource(resource)

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

.. decorator:: requires_docstrings

 Decorator for only running the test if :data:`HAVE_DOCSTRINGS`.

.. decorator:: cpython_only(test)

 Decorator for tests only applicable to CPython.

.. decorator:: impl_detail(msg=None, **guards)

 Decorator for invoking :func:`check_impl_detail` on *guards*. If that
 returns ``False``, then uses *msg* as the reason for skipping the test.

.. decorator:: no_tracing(func)

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

.. decorator:: 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.

.. decorator:: reap_threads(func)

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

.. decorator:: 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.

.. decorator:: bigaddrspacetest(f)

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

.. function:: make_bad_fd()

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

.. function:: check_syntax_error(testcase, statement, errtext='', *, lineno=None, offset=None)

 Test for syntax errors in *statement* by attempting to compile *statement*.
 *testcase* is the :mod:`unittest` instance for the test. *errtext* is the
 regular expression which should match the string representation of the
 raised :exc:`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.

.. function:: 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 :exc:`SyntaxWarning` is emitted only once, and that it
 will be converted to a :exc:`SyntaxError` when turned into error.
 *testcase* is the :mod:`unittest` instance for the test. *errtext* is the
 regular expression which should match the string representation of the
 emitted :exc:`SyntaxWarning` and raised :exc:`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.

 .. versionadded:: 3.8

.. function:: open_urlresource(url, *args, **kw)

 Open *url*. If open fails, raises :exc:`TestFailed`.

.. function:: import_module(name, deprecated=False, *, required_on())

 This function imports and returns the named module. Unlike a normal
 import, this function raises :exc:`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 :data:`sys.platform`.

 .. versionadded:: 3.1

.. function:: 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 :func:`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 :exc:`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 :exc:`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'])

 .. versionadded:: 3.1

.. function:: modules_setup()

 Return a copy of :data:`sys.modules`.

.. function:: modules_cleanup(oldmodules)

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

.. function:: threading_setup()

 Return current thread count and copy of dangling threads.

.. function:: 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.

.. function:: join_thread(thread, timeout=30.0)

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

.. function:: 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.

.. function:: get_attribute(obj, name)

 Get an attribute, raising :exc:`unittest.SkipTest` if :exc:`AttributeError`
 is raised.

.. function:: 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 :const:`~socket.AF_INET` and ``sock.type`` is
 :const:`~socket.SOCK_STREAM`, and the socket has
 :const:`~socket.SO_REUSEADDR` or :const:`~socket.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 :const:`~socket.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.

.. function:: bind_unix_socket(sock, addr)

 Bind a unix socket, raising :exc:`unittest.SkipTest` if
 :exc:`PermissionError` is raised.

.. function:: catch_threading_exception()

 Context manager catching :class:`threading.Thread` exception using
 :func:`threading.excepthook`.

 Attributes set when an exception is catched:

 * ``exc_type``
 * ``exc_value``
 * ``exc_traceback``
 * ``thread``

 See :func:`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)

 .. versionadded:: 3.8

.. function:: catch_unraisable_exception()

 Context manager catching unraisable exception using
 :func:`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)

 .. versionadded:: 3.8

.. function:: 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 :const:`~socket.AF_INET`,
 :const:`~socket.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 :func:`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 :func:`bind_port` over
 :func:`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.

.. function:: load_package_tests(pkg_dir, loader, standard_tests, pattern)

 Generic implementation of the :mod:`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)

.. function:: fs_is_case_insensitive(directory)

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

.. function:: 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 '__'.

 .. versionadded:: 3.5

.. function:: 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*.

.. function:: run_in_subinterp(code)

 Run *code* in subinterpreter. Raise :exc:`unittest.SkipTest` if
 :mod:`tracemalloc` is enabled.

.. function:: check_free_after_iterating(test, iter, cls, args=())

 Assert that *iter* is deallocated after iterating.

.. function:: 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.

.. function:: 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)

 .. versionadded:: 3.6

The :mod:`test.support` module defines the following classes:

Instances are a context manager that raises :exc:`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 :keyword:`with` statement. Only if all pairs match properly against attributes on the exception is :exc:`ResourceDenied` raised.

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.

.. versionchanged:: 3.1
 Added dictionary interface.

.. method:: EnvironmentVarGuard.set(envvar, value)

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

.. method:: EnvironmentVarGuard.unset(envvar)

 Temporarily unset the environment variable ``envvar``.

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 :func:`resource.setrlimit` is used to set :attr:`resource.RLIMIT_CORE`'s soft limit to 0 to prevent coredump file creation.

On both platforms, the old value is restored by :meth:`__exit__`.

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.

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

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

Note that all :data:`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 to save and restore signal handlers registered by the Python signal handler.

.. method:: matches(self, d, **kwargs)

 Try to match a single dict with the supplied arguments.

.. method:: match_value(self, k, dv, v)

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

Class used to record warnings for unit tests. See documentation of :func:`check_warnings` above for more details.

.. method:: run(test)

 Run *test* and return the result.

Class for logging support.

Simple :term:`path-like object`. It implements the :meth:`__fspath__` method which just returns the path argument. If path is an exception, it will be raised in :meth:`!__fspath__`.

:mod:`test.support.script_helper` --- Utilities for the Python execution tests

.. module:: test.support.script_helper
 :synopsis: Support for Python's script execution tests.

The :mod:`test.support.script_helper` module provides support for Python's script execution tests.

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

.. function:: 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``.

.. function:: 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``.

.. function:: 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 :func:`assert_python_ok` for more options.

.. function:: 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 :func:`subprocess.Popen`. Returns a
 :class:`subprocess.Popen` object.

.. function:: kill_python(p)

 Run the given :class:`subprocess.Popen` process until completion and return
 stdout.

.. function:: 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.

.. function:: 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)``.

.. function:: make_pkg(pkg_dir, init_source='')

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

.. function:: 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.

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