2 :mod:`test` --- Regression tests package for Python
3 ===================================================
6 :synopsis: Regression tests package containing the testing suite for Python.
7 .. sectionauthor:: Brett Cannon <brett@python.org>
10 The :mod:`test` package contains all regression tests for Python as well as the
11 modules :mod:`test.test_support` and :mod:`test.regrtest`.
12 :mod:`test.test_support` is used to enhance your tests while
13 :mod:`test.regrtest` drives the testing suite.
15 Each module in the :mod:`test` package whose name starts with ``test_`` is a
16 testing suite for a specific module or feature. All new tests should be written
17 using the :mod:`unittest` or :mod:`doctest` module. Some older tests are
18 written using a "traditional" testing style that compares output printed to
19 ``sys.stdout``; this style of test is considered deprecated.
24 Module :mod:`unittest`
25 Writing PyUnit regression tests.
28 Tests embedded in documentation strings.
33 Writing Unit Tests for the :mod:`test` package
34 ----------------------------------------------
36 It is preferred that tests that use the :mod:`unittest` module follow a few
37 guidelines. One is to name the test module by starting it with ``test_`` and end
38 it with the name of the module being tested. The test methods in the test module
39 should start with ``test_`` and end with a description of what the method is
40 testing. This is needed so that the methods are recognized by the test driver as
41 test methods. Also, no documentation string for the method should be included. A
42 comment (such as ``# Tests function returns only True or False``) should be used
43 to provide documentation for test methods. This is done because documentation
44 strings get printed out if they exist and thus what test is being run is not
47 A basic boilerplate is often used::
50 from test import test_support
52 class MyTestCase1(unittest.TestCase):
54 # Only use setUp() and tearDown() if necessary
57 ... code to execute in preparation for tests ...
60 ... code to execute to clean up after tests ...
62 def test_feature_one(self):
66 def test_feature_two(self):
70 ... more test methods ...
72 class MyTestCase2(unittest.TestCase):
73 ... same structure as MyTestCase1 ...
75 ... more test classes ...
78 test_support.run_unittest(MyTestCase1,
80 ... list other tests ...
83 if __name__ == '__main__':
86 This boilerplate code allows the testing suite to be run by :mod:`test.regrtest`
87 as well as on its own as a script.
89 The goal for regression testing is to try to break code. This leads to a few
90 guidelines to be followed:
92 * The testing suite should exercise all classes, functions, and constants. This
93 includes not just the external API that is to be presented to the outside world
94 but also "private" code.
96 * Whitebox testing (examining the code being tested when the tests are being
97 written) is preferred. Blackbox testing (testing only the published user
98 interface) is not complete enough to make sure all boundary and edge cases are
101 * Make sure all possible values are tested including invalid ones. This makes
102 sure that not only all valid values are acceptable but also that improper values
103 are handled correctly.
105 * Exhaust as many code paths as possible. Test where branching occurs and thus
106 tailor input to make sure as many different paths through the code are taken.
108 * Add an explicit test for any bugs discovered for the tested code. This will
109 make sure that the error does not crop up again if the code is changed in the
112 * Make sure to clean up after your tests (such as close and remove all temporary
115 * If a test is dependent on a specific condition of the operating system then
116 verify the condition already exists before attempting the test.
118 * Import as few modules as possible and do it as soon as possible. This
119 minimizes external dependencies of tests and also minimizes possible anomalous
120 behavior from side-effects of importing a module.
122 * Try to maximize code reuse. On occasion, tests will vary by something as small
123 as what type of input is used. Minimize code duplication by subclassing a basic
124 test class with a class that specifies the input::
126 class TestFuncAcceptsSequences(unittest.TestCase):
128 func = mySuperWhammyFunction
133 class AcceptLists(TestFuncAcceptsSequences):
136 class AcceptStrings(TestFuncAcceptsSequences):
139 class AcceptTuples(TestFuncAcceptsSequences):
145 Test Driven Development
146 A book by Kent Beck on writing tests before code.
151 Running tests using :mod:`test.regrtest`
152 ----------------------------------------
154 :mod:`test.regrtest` can be used as a script to drive Python's regression test
155 suite. Running the script by itself automatically starts running all regression
156 tests in the :mod:`test` package. It does this by finding all modules in the
157 package whose name starts with ``test_``, importing them, and executing the
158 function :func:`test_main` if present. The names of tests to execute may also be
159 passed to the script. Specifying a single regression test (:program:`python
160 regrtest.py` :option:`test_spam.py`) will minimize output and only print whether
161 the test passed or failed and thus minimize output.
163 Running :mod:`test.regrtest` directly allows what resources are available for
164 tests to use to be set. You do this by using the :option:`-u` command-line
165 option. Run :program:`python regrtest.py` :option:`-uall` to turn on all
166 resources; specifying :option:`all` as an option for :option:`-u` enables all
167 possible resources. If all but one resource is desired (a more common case), a
168 comma-separated list of resources that are not desired may be listed after
169 :option:`all`. The command :program:`python regrtest.py`
170 :option:`-uall,-audio,-largefile` will run :mod:`test.regrtest` with all
171 resources except the :option:`audio` and :option:`largefile` resources. For a
172 list of all resources and more command-line options, run :program:`python
173 regrtest.py` :option:`-h`.
175 Some other ways to execute the regression tests depend on what platform the
176 tests are being executed on. On Unix, you can run :program:`make` :option:`test`
177 at the top-level directory where Python was built. On Windows, executing
178 :program:`rt.bat` from your :file:`PCBuild` directory will run all regression
182 :mod:`test.test_support` --- Utility functions for tests
183 ========================================================
185 .. module:: test.test_support
186 :synopsis: Support for Python regression tests.
190 The :mod:`test.test_support` module has been renamed to :mod:`test.support`
191 in Python 3.0. The :term:`2to3` tool will automatically adapt imports when
192 converting your sources to 3.0.
197 The :mod:`test.test_support` module provides support for Python's regression
200 This module defines the following exceptions:
203 .. exception:: TestFailed
205 Exception to be raised when a test fails. This is deprecated in favor of
206 :mod:`unittest`\ -based tests and :class:`unittest.TestCase`'s assertion
210 .. exception:: TestSkipped
212 Subclass of :exc:`TestFailed`. Raised when a test is skipped. This occurs when a
213 needed resource (such as a network connection) is not available at the time of
217 .. exception:: ResourceDenied
219 Subclass of :exc:`TestSkipped`. Raised when a resource (such as a network
220 connection) is not available. Raised by the :func:`requires` function.
222 The :mod:`test.test_support` module defines the following constants:
227 :const:`True` when verbose output is enabled. Should be checked when more
228 detailed information is desired about a running test. *verbose* is set by
229 :mod:`test.regrtest`.
232 .. data:: have_unicode
234 :const:`True` when Unicode support is available.
239 :const:`True` if the running interpreter is Jython.
244 Set to the path that a temporary file may be created at. Any temporary that is
245 created should be closed and unlinked (removed).
247 The :mod:`test.test_support` module defines the following functions:
250 .. function:: forget(module_name)
252 Removes the module named *module_name* from ``sys.modules`` and deletes any
253 byte-compiled files of the module.
256 .. function:: is_resource_enabled(resource)
258 Returns :const:`True` if *resource* is enabled and available. The list of
259 available resources is only set when :mod:`test.regrtest` is executing the
263 .. function:: requires(resource[, msg])
265 Raises :exc:`ResourceDenied` if *resource* is not available. *msg* is the
266 argument to :exc:`ResourceDenied` if it is raised. Always returns true if called
267 by a function whose ``__name__`` is ``'__main__'``. Used when tests are executed
268 by :mod:`test.regrtest`.
271 .. function:: findfile(filename)
273 Return the path to the file named *filename*. If no match is found *filename* is
274 returned. This does not equal a failure since it could be the path to the file.
277 .. function:: run_unittest(*classes)
279 Execute :class:`unittest.TestCase` subclasses passed to the function. The
280 function scans the classes for methods starting with the prefix ``test_`` and
281 executes the tests individually.
283 It is also legal to pass strings as parameters; these should be keys in
284 ``sys.modules``. Each associated module will be scanned by
285 ``unittest.TestLoader.loadTestsFromModule()``. This is usually seen in the
286 following :func:`test_main` function::
289 test_support.run_unittest(__name__)
291 This will run all tests defined in the named module.
294 .. function:: check_warnings()
296 A convenience wrapper for ``warnings.catch_warnings()`` that makes
297 it easier to test that a warning was correctly raised with a single
298 assertion. It is approximately equivalent to calling
299 ``warnings.catch_warnings(record=True)``.
301 The main difference is that on entry to the context manager, a
302 :class:`WarningRecorder` instance is returned instead of a simple list.
303 The underlying warnings list is available via the recorder object's
304 :attr:`warnings` attribute, while the attributes of the last raised
305 warning are also accessible directly on the object. If no warning has
306 been raised, then the latter attributes will all be :const:`None`.
308 A :meth:`reset` method is also provided on the recorder object. This
309 method simply clears the warning list.
311 The context manager is used like this::
313 with check_warnings() as w:
314 warnings.simplefilter("always")
316 assert str(w.message) == "foo"
318 assert str(w.message) == "bar"
319 assert str(w.warnings[0].message) == "foo"
320 assert str(w.warnings[1].message) == "bar"
322 assert len(w.warnings) == 0
324 .. versionadded:: 2.6
327 .. function:: captured_stdout()
329 This is a context manager than runs the :keyword:`with` statement body using
330 a :class:`StringIO.StringIO` object as sys.stdout. That object can be
331 retrieved using the ``as`` clause of the :keyword:`with` statement.
335 with captured_stdout() as s:
337 assert s.getvalue() == "hello"
339 .. versionadded:: 2.6
342 .. function:: import_module(name, deprecated=False)
344 This function imports and returns the named module. Unlike a normal
345 import, this function raises :exc:`unittest.SkipTest` if the module
348 Module and package deprecation messages are suppressed during this import
349 if *deprecated* is :const:`True`.
351 .. versionadded:: 2.7
354 .. function:: import_fresh_module(name, fresh=(), blocked=(), deprecated=False)
356 This function imports and returns a fresh copy of the named Python module
357 by removing the named module from ``sys.modules`` before doing the import.
358 Note that unlike :func:`reload`, the original module is not affected by
361 *fresh* is an iterable of additional module names that are also removed
362 from the ``sys.modules`` cache before doing the import.
364 *blocked* is an iterable of module names that are replaced with :const:`0`
365 in the module cache during the import to ensure that attempts to import
366 them raise :exc:`ImportError`.
368 The named module and any modules named in the *fresh* and *blocked*
369 parameters are saved before starting the import and then reinserted into
370 ``sys.modules`` when the fresh import is complete.
372 Module and package deprecation messages are suppressed during this import
373 if *deprecated* is :const:`True`.
375 This function will raise :exc:`unittest.SkipTest` is the named module
380 # Get copies of the warnings module for testing without
381 # affecting the version being used by the rest of the test suite
382 # One copy uses the C implementation, the other is forced to use
383 # the pure Python fallback implementation
384 py_warnings = import_fresh_module('warnings', blocked=['_warnings'])
385 c_warnings = import_fresh_module('warnings', fresh=['_warnings'])
387 .. versionadded:: 2.7
390 The :mod:`test.test_support` module defines the following classes:
392 .. class:: TransientResource(exc[, **kwargs])
394 Instances are a context manager that raises :exc:`ResourceDenied` if the
395 specified exception type is raised. Any keyword arguments are treated as
396 attribute/value pairs to be compared against any exception raised within the
397 :keyword:`with` statement. Only if all pairs match properly against
398 attributes on the exception is :exc:`ResourceDenied` raised.
400 .. versionadded:: 2.6
401 .. class:: EnvironmentVarGuard()
403 Class used to temporarily set or unset environment variables. Instances can be
404 used as a context manager and have a complete dictionary interface for
405 querying/modifying the underlying ``os.environ``. After exit from the context
406 manager all changes to environment variables done through this instance will
409 .. versionadded:: 2.6
410 .. versionchanged:: 2.7
411 Added dictionary interface.
414 .. method:: EnvironmentVarGuard.set(envvar, value)
416 Temporarily set the environment variable ``envvar`` to the value of ``value``.
419 .. method:: EnvironmentVarGuard.unset(envvar)
421 Temporarily unset the environment variable ``envvar``.
424 .. class:: WarningsRecorder()
426 Class used to record warnings for unit tests. See documentation of
427 :func:`check_warnings` above for more details.
429 .. versionadded:: 2.6