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Edit: /usr/share/doc/python3-docs/html/_sources/library/test.rst.txt (25764B)
:mod:`test` --- Regression tests package for Python
===================================================
.. module:: test
:synopsis: Regression tests package containing the testing suite for Python.
.. sectionauthor:: Brett Cannon
.. note::
The :mod:`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 :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-tests:
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.
.. _regrtest:
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.
.. note::
:mod:`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:: 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:: 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).
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:: 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:: 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:: 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:: 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)
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``.
.. 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:: 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:: can_symlink()
Return ``True`` if the OS supports symbolic links, ``False``
otherwise.
.. decorator:: skip_unless_symlink
A decorator for running tests that require support for symbolic links.
.. 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.
.. function:: make_bad_fd()
Create an invalid file descriptor by opening and closing a temporary file,
and returning its descriptor.
.. function:: import_module(name, deprecated=False)
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``.
.. 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:: 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:: 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:: 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:: 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 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:
.. class:: TransientResource(exc, **kwargs)
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:: 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.
.. 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``.
.. class:: 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, :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__`.
.. class:: WarningsRecorder()
Class used to record warnings for unit tests. See documentation of
:func:`check_warnings` above for more details.
.. class:: FakePath(path)
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__`.