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.
189 The :mod:`test.test_support` module provides support for Python's regression
192 This module defines the following exceptions:
195 .. exception:: TestFailed
197 Exception to be raised when a test fails. This is deprecated in favor of
198 :mod:`unittest`\ -based tests and :class:`unittest.TestCase`'s assertion
202 .. exception:: TestSkipped
204 Subclass of :exc:`TestFailed`. Raised when a test is skipped. This occurs when a
205 needed resource (such as a network connection) is not available at the time of
209 .. exception:: ResourceDenied
211 Subclass of :exc:`TestSkipped`. Raised when a resource (such as a network
212 connection) is not available. Raised by the :func:`requires` function.
214 The :mod:`test.test_support` module defines the following constants:
219 :const:`True` when verbose output is enabled. Should be checked when more
220 detailed information is desired about a running test. *verbose* is set by
221 :mod:`test.regrtest`.
224 .. data:: have_unicode
226 :const:`True` when Unicode support is available.
231 :const:`True` if the running interpreter is Jython.
236 Set to the path that a temporary file may be created at. Any temporary that is
237 created should be closed and unlinked (removed).
239 The :mod:`test.test_support` module defines the following functions:
242 .. function:: forget(module_name)
244 Removes the module named *module_name* from ``sys.modules`` and deletes any
245 byte-compiled files of the module.
248 .. function:: is_resource_enabled(resource)
250 Returns :const:`True` if *resource* is enabled and available. The list of
251 available resources is only set when :mod:`test.regrtest` is executing the
255 .. function:: requires(resource[, msg])
257 Raises :exc:`ResourceDenied` if *resource* is not available. *msg* is the
258 argument to :exc:`ResourceDenied` if it is raised. Always returns true if called
259 by a function whose ``__name__`` is ``'__main__'``. Used when tests are executed
260 by :mod:`test.regrtest`.
263 .. function:: findfile(filename)
265 Return the path to the file named *filename*. If no match is found *filename* is
266 returned. This does not equal a failure since it could be the path to the file.
269 .. function:: run_unittest(*classes)
271 Execute :class:`unittest.TestCase` subclasses passed to the function. The
272 function scans the classes for methods starting with the prefix ``test_`` and
273 executes the tests individually.
275 It is also legal to pass strings as parameters; these should be keys in
276 ``sys.modules``. Each associated module will be scanned by
277 ``unittest.TestLoader.loadTestsFromModule()``. This is usually seen in the
278 following :func:`test_main` function::
281 test_support.run_unittest(__name__)
283 This will run all tests defined in the named module.
286 .. function:: catch_warning(record=True)
288 Return a context manager that guards the warnings filter from being
289 permanently changed and records the data of the last warning that has been
290 issued. The ``record`` argument specifies whether any raised warnings are
291 captured by the object returned by :func:`warnings.catch_warning` or allowed
292 to propagate as normal.
294 The context manager is typically used like this::
296 with catch_warning() as w:
298 assert str(w.message) == "foo"
300 .. versionadded:: 2.6
303 .. function:: captured_stdout()
305 This is a context manager than runs the :keyword:`with` statement body using
306 a :class:`StringIO.StringIO` object as sys.stdout. That object can be
307 retrieved using the ``as`` clause of the :keyword:`with` statement.
311 with captured_stdout() as s:
313 assert s.getvalue() == "hello"
315 .. versionadded:: 2.6
318 The :mod:`test.test_support` module defines the following classes:
320 .. class:: TransientResource(exc[, **kwargs])
322 Instances are a context manager that raises :exc:`ResourceDenied` if the
323 specified exception type is raised. Any keyword arguments are treated as
324 attribute/value pairs to be compared against any exception raised within the
325 :keyword:`with` statement. Only if all pairs match properly against
326 attributes on the exception is :exc:`ResourceDenied` raised.
328 .. versionadded:: 2.6
331 .. class:: EnvironmentVarGuard()
333 Class used to temporarily set or unset environment variables. Instances can be
334 used as a context manager.
336 .. versionadded:: 2.6
339 .. method:: EnvironmentVarGuard.set(envvar, value)
341 Temporarily set the environment variable ``envvar`` to the value of ``value``.
344 .. method:: EnvironmentVarGuard.unset(envvar)
346 Temporarily unset the environment variable ``envvar``.