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diff --git a/Lib/test/README b/Lib/test/README index 40837e4..6ecd593 100644 --- a/Lib/test/README +++ b/Lib/test/README @@ -1,10 +1,12 @@ - Writing Python Regression Tests - ------------------------------- - Skip Montanaro - (skip@mojam.com) ++++++++++++++++++++++++++++++++ +Writing Python Regression Tests ++++++++++++++++++++++++++++++++ +:Author: Skip Montanaro +:Contact: skip@mojam.com Introduction +============ If you add a new module to Python or modify the functionality of an existing module, you should write one or more test cases to exercise that new @@ -13,8 +15,8 @@ testing facility provided with Python; any particular test should use only one of these options. Each option requires writing a test module using the conventions of the the selected option: - - PyUnit based tests - - doctest based tests + - PyUnit_ based tests + - doctest_ based tests - "traditional" Python test modules Regardless of the mechanics of the testing approach you choose, @@ -26,26 +28,33 @@ your test cases to exercise it more completely. In particular, you will be able to refer to the C and Python code in the CVS repository when writing your regression test cases. +.. _PyUnit: +.. _unittest: http://www.python.org/doc/current/lib/module-unittest.html +.. _doctest: http://www.python.org/doc/current/lib/module-doctest.html PyUnit based tests - -The PyUnit framework is based on the ideas of unit testing as espoused -by Kent Beck and the Extreme Programming (XP) movement. The specific -interface provided by the framework is tightly based on the JUnit +------------------ +The PyUnit_ framework is based on the ideas of unit testing as espoused +by Kent Beck and the `Extreme Programming`_ (XP) movement. The specific +interface provided by the framework is tightly based on the JUnit_ Java implementation of Beck's original SmallTalk test framework. Please -see the documentation of the unittest module for detailed information on +see the documentation of the unittest_ module for detailed information on the interface and general guidelines on writing PyUnit based tests. The test_support helper module provides a two functions for use by PyUnit based tests in the Python regression testing framework: -run_unittest() takes a unittest.TestCase derived class as a parameter -and runs the tests defined in that class, and run_suite() takes a -populated TestSuite instance and runs the tests. run_suite() is -preferred because unittest files typically grow multiple test classes, -and you might as well be prepared. + +- ``run_unittest()`` takes a ``unittest.TestCase`` derived class as a + parameter and runs the tests defined in that class + +- ``run_suite()`` takes a populated ``TestSuite`` instance and runs the + tests + +``run_suite()`` is preferred because unittest files typically grow multiple +test classes, and you might as well be prepared. All test methods in the Python regression framework have names that -start with "test_" and use lower-case names with words separated with +start with "``test_``" and use lower-case names with words separated with underscores. Test methods should *not* have docstrings! The unittest module prints @@ -55,7 +64,7 @@ latter information makes it easier to find the source for the test than the docstring. All PyUnit-based tests in the Python test suite use boilerplate that -looks like this (with minor variations): +looks like this (with minor variations):: import unittest from test import test_support @@ -101,17 +110,19 @@ This has the advantage that it allows the unittest module to be used as a script to run individual tests as well as working well with the regrtest framework. +.. _Extreme Programming: http://www.extremeprogramming.org/ +.. _JUnit: http://www.junit.org/ doctest based tests - -Tests written to use doctest are actually part of the docstrings for +------------------- +Tests written to use doctest_ are actually part of the docstrings for the module being tested. Each test is written as a display of an interactive session, including the Python prompts, statements that would be typed by the user, and the output of those statements (including tracebacks, although only the exception msg needs to be retained then). The module in the test package is simply a wrapper that causes doctest to run over the tests in the module. The test for the difflib module -provides a convenient example: +provides a convenient example:: import difflib from test import test_support @@ -122,12 +133,12 @@ create a corresponding output/test_difflib file), but running regrtest with -v will give a detailed report, the same as if passing -v to doctest. A second argument can be passed to run_doctest to tell doctest to search -sys.argv for -v instead of using test_support's idea of verbosity. This +``sys.argv`` for -v instead of using test_support's idea of verbosity. This is useful for writing doctest-based tests that aren't simply running a doctest'ed Lib module, but contain the doctests themselves. Then at times you may want to run such a test directly as a doctest, independent of the regrtest framework. The tail end of test_descrtut.py is a good -example: +example:: def test_main(verbose=None): from test import test_support, test_descrtut @@ -136,34 +147,32 @@ example: if __name__ == "__main__": test_main(1) -If run via regrtest, test_main() is called (by regrtest) without specifying -verbose, and then test_support's idea of verbosity is used. But when -run directly, test_main(1) is called, and then doctest's idea of verbosity -is used. +If run via regrtest, ``test_main()`` is called (by regrtest) without +specifying verbose, and then test_support's idea of verbosity is used. But +when run directly, ``test_main(1)`` is called, and then doctest's idea of +verbosity is used. See the documentation for the doctest module for information on writing tests using the doctest framework. - "traditional" Python test modules - +--------------------------------- The mechanics of how the "traditional" test system operates are fairly straightforward. When a test case is run, the output is compared with the expected output that is stored in .../Lib/test/output. If the test runs to completion and the actual and expected outputs match, the test succeeds, if -not, it fails. If an ImportError or test_support.TestSkipped error is -raised, the test is not run. - +not, it fails. If an ``ImportError`` or ``test_support.TestSkipped`` error +is raised, the test is not run. Executing Test Cases - +==================== If you are writing test cases for module spam, you need to create a file in .../Lib/test named test_spam.py. In addition, if the tests are expected to write to stdout during a successful run, you also need to create an expected output file in .../Lib/test/output named test_spam ("..." represents the top-level directory in the Python source tree, the directory containing the configure script). If needed, generate the initial version -of the test output file by executing: +of the test output file by executing:: ./python Lib/test/regrtest.py -g test_spam.py @@ -176,28 +185,28 @@ not to have an expected-out file (note that doctest- and unittest-based tests do not). To run a single test after modifying a module, simply run regrtest.py -without the -g flag: +without the -g flag:: ./python Lib/test/regrtest.py test_spam.py While debugging a regression test, you can of course execute it -independently of the regression testing framework and see what it prints: +independently of the regression testing framework and see what it prints:: ./python Lib/test/test_spam.py To run the entire test suite: -[UNIX, + other platforms where "make" works] Make the "test" target at the -top level: +- [UNIX, + other platforms where "make" works] Make the "test" target at the + top level:: make test -[WINDOWS] Run rt.bat from your PCBuild directory. Read the comments at -the top of rt.bat for the use of special -d, -O and -q options processed -by rt.bat. +- [WINDOWS] Run rt.bat from your PCBuild directory. Read the comments at + the top of rt.bat for the use of special -d, -O and -q options processed + by rt.bat. -[OTHER] You can simply execute the two runs of regrtest (optimized and -non-optimized) directly: +- [OTHER] You can simply execute the two runs of regrtest (optimized and + non-optimized) directly:: ./python Lib/test/regrtest.py ./python -O Lib/test/regrtest.py @@ -217,11 +226,11 @@ significant digits (unless you understand what you are doing!). Test Case Writing Tips - +====================== Writing good test cases is a skilled task and is too complex to discuss in detail in this short document. Many books have been written on the subject. -I'll show my age by suggesting that Glenford Myers' "The Art of Software -Testing", published in 1979, is still the best introduction to the subject +I'll show my age by suggesting that Glenford Myers' `"The Art of Software +Testing"`_, published in 1979, is still the best introduction to the subject available. It is short (177 pages), easy to read, and discusses the major elements of software testing, though its publication predates the object-oriented software revolution, so doesn't cover that subject at all. @@ -264,36 +273,38 @@ In designing test cases you should pay attention to the following: fixing it). * If you need to create a temporary file, you can use the filename in - test_support.TESTFN to do so. It is important to remove the file + ``test_support.TESTFN`` to do so. It is important to remove the file when done; other tests should be able to use the name without cleaning up after your test. +.. _"The Art of Software Testing": + http://www.amazon.com/exec/obidos/ISBN=0471043281 Regression Test Writing Rules - +============================= Each test case is different. There is no "standard" form for a Python regression test case, though there are some general rules (note that -these mostly apply only to the "classic" tests; unittest- and doctest- -based tests should follow the conventions natural to those frameworks): +these mostly apply only to the "classic" tests; unittest_- and doctest_- +based tests should follow the conventions natural to those frameworks):: - * If your test case detects a failure, raise TestFailed (found in - test.test_support). + * If your test case detects a failure, raise ``TestFailed`` (found in + ``test.test_support``). * Import everything you'll need as early as possible. * If you'll be importing objects from a module that is at least partially platform-dependent, only import those objects you need for - the current test case to avoid spurious ImportError exceptions that - prevent the test from running to completion. + the current test case to avoid spurious ``ImportError`` exceptions + that prevent the test from running to completion. - * Print all your test case results using the print statement. For + * Print all your test case results using the ``print`` statement. For non-fatal errors, print an error message (or omit a successful completion print) to indicate the failure, but proceed instead of - raising TestFailed. + raising ``TestFailed``. - * Use "assert" sparingly, if at all. It's usually better to just print + * Use ``assert`` sparingly, if at all. It's usually better to just print what you got, and rely on regrtest's got-vs-expected comparison to - catch deviations from what you expect. assert statements aren't + catch deviations from what you expect. ``assert`` statements aren't executed at all when regrtest is run in -O mode; and, because they cause the test to stop immediately, can lead to a long & tedious test-fix, test-fix, test-fix, ... cycle when things are badly broken @@ -301,59 +312,59 @@ based tests should follow the conventions natural to those frameworks): for the first time on new platforms or under new implementations of the language). - Miscellaneous - +============= There is a test_support module in the test package you can import for -your test case. Import this module using either +your test case. Import this module using either:: import test.test_support -or +or:: from test import test_support test_support provides the following useful objects: - * TestFailed - raise this exception when your regression test detects a - failure. + * ``TestFailed`` - raise this exception when your regression test detects + a failure. - * TestSkipped - raise this if the test could not be run because the + * ``TestSkipped`` - raise this if the test could not be run because the platform doesn't offer all the required facilities (like large file support), even if all the required modules are available. - * verbose - you can use this variable to control print output. Many + * ``verbose`` - you can use this variable to control print output. Many modules use it. Search for "verbose" in the test_*.py files to see lots of examples. - * verify(condition, reason='test failed'). Use this instead of + * ``verify(condition, reason='test failed')``. Use this instead of:: assert condition[, reason] - verify() has two advantages over assert: it works even in -O mode, - and it raises TestFailed on failure instead of AssertionError. + ``verify()`` has two advantages over ``assert``: it works even in -O + mode, and it raises ``TestFailed`` on failure instead of + ``AssertionError``. - * TESTFN - a string that should always be used as the filename when you - need to create a temp file. Also use try/finally to ensure that your - temp files are deleted before your test completes. Note that you - cannot unlink an open file on all operating systems, so also be sure - to close temp files before trying to unlink them. + * ``TESTFN`` - a string that should always be used as the filename when + you need to create a temp file. Also use ``try``/``finally`` to + ensure that your temp files are deleted before your test completes. + Note that you cannot unlink an open file on all operating systems, so + also be sure to close temp files before trying to unlink them. - * sortdict(dict) - acts like repr(dict.items()), but sorts the items - first. This is important when printing a dict value, because the - order of items produced by dict.items() is not defined by the + * ``sortdict(dict)`` - acts like ``repr(dict.items())``, but sorts the + items first. This is important when printing a dict value, because + the order of items produced by ``dict.items()`` is not defined by the language. - * findfile(file) - you can call this function to locate a file somewhere - along sys.path or in the Lib/test tree - see test_linuxaudiodev.py for - an example of its use. + * ``findfile(file)`` - you can call this function to locate a file + somewhere along sys.path or in the Lib/test tree - see + test_linuxaudiodev.py for an example of its use. - * use_large_resources - true iff tests requiring large time or space + * ``use_large_resources`` - true iff tests requiring large time or space should be run. - * fcmp(x,y) - you can call this function to compare two floating point - numbers when you expect them to only be approximately equal withing a - fuzz factor (test_support.FUZZ, which defaults to 1e-6). + * ``fcmp(x,y)`` - you can call this function to compare two floating + point numbers when you expect them to only be approximately equal + withing a fuzz factor (``test_support.FUZZ``, which defaults to 1e-6). Python and C statement coverage results are currently available at @@ -365,9 +376,8 @@ You can refer to the summaries and the test coverage output files to see where coverage is adequate or lacking and write test cases to beef up the coverage. - Some Non-Obvious regrtest Features - +================================== * Automagic test detection: When you create a new test file test_spam.py, you do not need to modify regrtest (or anything else) to advertise its existence. regrtest searches for and runs all @@ -385,13 +395,13 @@ Some Non-Obvious regrtest Features * Two-stage testing: To run test_spam.py, regrtest imports test_spam as a module. Most tests run to completion as a side-effect of getting imported. After importing test_spam, regrtest also executes - test_spam.test_main(), if test_spam has a "test_main" attribute. + ``test_spam.test_main()``, if test_spam has a ``test_main`` attribute. This is rarely required with the "traditional" Python tests, and you shouldn't create a module global with name test_main unless you're specifically exploiting this gimmick. This usage does prove useful with PyUnit-based tests as well, however; defining - a test_main() which is run by regrtest and a script-stub in the - test module ("if __name__ == '__main__': test_main()") allows + a ``test_main()`` which is run by regrtest and a script-stub in the + test module ("``if __name__ == '__main__': test_main()``") allows the test to be used like any other Python test and also work with the unittest.py-as-a-script approach, allowing a developer to run specific tests from the command line. |