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:mod:`test` --- Regression tests package for Python
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===================================================
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:synopsis: Regression tests package containing the testing suite for Python.
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.. sectionauthor:: Brett Cannon <brett@python.org>
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The :mod:`test` package contains all regression tests for Python as well as the
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modules :mod:`test.test_support` and :mod:`test.regrtest`.
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:mod:`test.test_support` is used to enhance your tests while
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:mod:`test.regrtest` drives the testing suite.
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Each module in the :mod:`test` package whose name starts with ``test_`` is a
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testing suite for a specific module or feature. All new tests should be written
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using the :mod:`unittest` or :mod:`doctest` module. Some older tests are
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written using a "traditional" testing style that compares output printed to
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``sys.stdout``; this style of test is considered deprecated.
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Module :mod:`unittest`
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Writing PyUnit regression tests.
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Tests embedded in documentation strings.
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Writing Unit Tests for the :mod:`test` package
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----------------------------------------------
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It is preferred that tests that use the :mod:`unittest` module follow a few
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guidelines. One is to name the test module by starting it with ``test_`` and end
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it with the name of the module being tested. The test methods in the test module
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should start with ``test_`` and end with a description of what the method is
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testing. This is needed so that the methods are recognized by the test driver as
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test methods. Also, no documentation string for the method should be included. A
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comment (such as ``# Tests function returns only True or False``) should be used
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to provide documentation for test methods. This is done because documentation
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strings get printed out if they exist and thus what test is being run is not
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A basic boilerplate is often used::
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from test import test_support
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class MyTestCase1(unittest.TestCase):
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# Only use setUp() and tearDown() if necessary
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... code to execute in preparation for tests ...
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... code to execute to clean up after tests ...
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def test_feature_one(self):
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def test_feature_two(self):
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... more test methods ...
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class MyTestCase2(unittest.TestCase):
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... same structure as MyTestCase1 ...
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... more test classes ...
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test_support.run_unittest(MyTestCase1,
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... list other tests ...
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if __name__ == '__main__':
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This boilerplate code allows the testing suite to be run by :mod:`test.regrtest`
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as well as on its own as a script.
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The goal for regression testing is to try to break code. This leads to a few
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guidelines to be followed:
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* The testing suite should exercise all classes, functions, and constants. This
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includes not just the external API that is to be presented to the outside world
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but also "private" code.
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* Whitebox testing (examining the code being tested when the tests are being
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written) is preferred. Blackbox testing (testing only the published user
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interface) is not complete enough to make sure all boundary and edge cases are
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* Make sure all possible values are tested including invalid ones. This makes
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sure that not only all valid values are acceptable but also that improper values
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are handled correctly.
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* Exhaust as many code paths as possible. Test where branching occurs and thus
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tailor input to make sure as many different paths through the code are taken.
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* Add an explicit test for any bugs discovered for the tested code. This will
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make sure that the error does not crop up again if the code is changed in the
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* Make sure to clean up after your tests (such as close and remove all temporary
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* If a test is dependent on a specific condition of the operating system then
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verify the condition already exists before attempting the test.
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* Import as few modules as possible and do it as soon as possible. This
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minimizes external dependencies of tests and also minimizes possible anomalous
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behavior from side-effects of importing a module.
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* Try to maximize code reuse. On occasion, tests will vary by something as small
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as what type of input is used. Minimize code duplication by subclassing a basic
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test class with a class that specifies the input::
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class TestFuncAcceptsSequences(unittest.TestCase):
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func = mySuperWhammyFunction
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class AcceptLists(TestFuncAcceptsSequences):
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class AcceptStrings(TestFuncAcceptsSequences):
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class AcceptTuples(TestFuncAcceptsSequences):
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Test Driven Development
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A book by Kent Beck on writing tests before code.
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Running tests using :mod:`test.regrtest`
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----------------------------------------
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:mod:`test.regrtest` can be used as a script to drive Python's regression test
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suite. Running the script by itself automatically starts running all regression
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tests in the :mod:`test` package. It does this by finding all modules in the
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package whose name starts with ``test_``, importing them, and executing the
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function :func:`test_main` if present. The names of tests to execute may also be
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passed to the script. Specifying a single regression test (:program:`python
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regrtest.py` :option:`test_spam.py`) will minimize output and only print whether
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the test passed or failed and thus minimize output.
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Running :mod:`test.regrtest` directly allows what resources are available for
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tests to use to be set. You do this by using the :option:`-u` command-line
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option. Run :program:`python regrtest.py` :option:`-uall` to turn on all
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resources; specifying :option:`all` as an option for :option:`-u` enables all
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possible resources. If all but one resource is desired (a more common case), a
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comma-separated list of resources that are not desired may be listed after
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:option:`all`. The command :program:`python regrtest.py`
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:option:`-uall,-audio,-largefile` will run :mod:`test.regrtest` with all
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resources except the :option:`audio` and :option:`largefile` resources. For a
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list of all resources and more command-line options, run :program:`python
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regrtest.py` :option:`-h`.
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Some other ways to execute the regression tests depend on what platform the
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tests are being executed on. On Unix, you can run :program:`make` :option:`test`
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at the top-level directory where Python was built. On Windows, executing
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:program:`rt.bat` from your :file:`PCBuild` directory will run all regression
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:mod:`test.support` --- Utility functions for tests
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========================================================
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.. module:: test.support
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:synopsis: Support for Python regression tests.
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The :mod:`test.support` module provides support for Python's regression
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This module defines the following exceptions:
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.. exception:: TestFailed
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Exception to be raised when a test fails. This is deprecated in favor of
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:mod:`unittest`\ -based tests and :class:`unittest.TestCase`'s assertion
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.. exception:: TestSkipped
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Subclass of :exc:`TestFailed`. Raised when a test is skipped. This occurs when a
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needed resource (such as a network connection) is not available at the time of
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.. exception:: ResourceDenied
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Subclass of :exc:`TestSkipped`. Raised when a resource (such as a network
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connection) is not available. Raised by the :func:`requires` function.
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The :mod:`test.support` module defines the following constants:
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:const:`True` when verbose output is enabled. Should be checked when more
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detailed information is desired about a running test. *verbose* is set by
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:mod:`test.regrtest`.
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:const:`True` if the running interpreter is Jython.
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Set to the path that a temporary file may be created at. Any temporary that is
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created should be closed and unlinked (removed).
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The :mod:`test.support` module defines the following functions:
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.. function:: forget(module_name)
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Removes the module named *module_name* from ``sys.modules`` and deletes any
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byte-compiled files of the module.
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.. function:: is_resource_enabled(resource)
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Returns :const:`True` if *resource* is enabled and available. The list of
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available resources is only set when :mod:`test.regrtest` is executing the
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.. function:: requires(resource[, msg])
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Raises :exc:`ResourceDenied` if *resource* is not available. *msg* is the
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argument to :exc:`ResourceDenied` if it is raised. Always returns true if called
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by a function whose ``__name__`` is ``'__main__'``. Used when tests are executed
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by :mod:`test.regrtest`.
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.. function:: findfile(filename)
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Return the path to the file named *filename*. If no match is found *filename* is
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returned. This does not equal a failure since it could be the path to the file.
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.. function:: run_unittest(*classes)
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Execute :class:`unittest.TestCase` subclasses passed to the function. The
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function scans the classes for methods starting with the prefix ``test_`` and
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executes the tests individually.
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It is also legal to pass strings as parameters; these should be keys in
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``sys.modules``. Each associated module will be scanned by
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``unittest.TestLoader.loadTestsFromModule()``. This is usually seen in the
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following :func:`test_main` function::
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test_support.run_unittest(__name__)
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This will run all tests defined in the named module.
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.. function:: check_warnings()
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A convenience wrapper for ``warnings.catch_warnings()`` that makes
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it easier to test that a warning was correctly raised with a single
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assertion. It is approximately equivalent to calling
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``warnings.catch_warnings(record=True)``.
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The main difference is that on entry to the context manager, a
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:class:`WarningRecorder` instance is returned instead of a simple list.
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The underlying warnings list is available via the recorder object's
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:attr:`warnings` attribute, while the attributes of the last raised
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warning are also accessible directly on the object. If no warning has
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been raised, then the latter attributes will all be :const:`None`.
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A :meth:`reset` method is also provided on the recorder object. This
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method simply clears the warning list.
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The context manager is used like this::
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with check_warnings() as w:
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warnings.simplefilter("always")
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assert str(w.message) == "foo"
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assert str(w.message) == "bar"
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assert str(w.warnings[0].message) == "foo"
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assert str(w.warnings[1].message) == "bar"
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assert len(w.warnings) == 0
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.. function:: captured_stdout()
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This is a context manager than runs the :keyword:`with` statement body using
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a :class:`StringIO.StringIO` object as sys.stdout. That object can be
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retrieved using the ``as`` clause of the :keyword:`with` statement.
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with captured_stdout() as s:
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assert s.getvalue() == "hello"
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The :mod:`test.support` module defines the following classes:
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.. class:: TransientResource(exc[, **kwargs])
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Instances are a context manager that raises :exc:`ResourceDenied` if the
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specified exception type is raised. Any keyword arguments are treated as
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attribute/value pairs to be compared against any exception raised within the
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:keyword:`with` statement. Only if all pairs match properly against
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attributes on the exception is :exc:`ResourceDenied` raised.
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.. class:: EnvironmentVarGuard()
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Class used to temporarily set or unset environment variables. Instances can be
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used as a context manager.
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.. method:: EnvironmentVarGuard.set(envvar, value)
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Temporarily set the environment variable ``envvar`` to the value of ``value``.
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.. method:: EnvironmentVarGuard.unset(envvar)
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Temporarily unset the environment variable ``envvar``.
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.. class:: WarningsRecorder()
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Class used to record warnings for unit tests. See documentation of
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:func:`check_warnings` above for more details.
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Doc/library/test.rst
