[Python-Dev] PEP: Consolidating names in the `unittest` module (updated 2008-07-16)

[Ben Finney]

Significant changes are resolving to remove the 'fail*' names, giving
recommended name to use for each removed name, and further summary of
related discussion.


:PEP:               XXX
:Title:             Consolidating names in the `unittest` module
:Version:           0.3
:Last-Modified:     2008-07-16
:Author:            Ben Finney <ben+python at benfinney.id.au>
:Status:            Draft
:Type:              Standards Track
:Content-Type:      test/x-rst
:Created:           2008-07-14
:Python-Version:    2.7, 3.1
:Post-History:


..  contents::


Abstract
========

This PEP proposes to consolidate the names that constitute the API of
the standard library `unittest` module, with the goal of removing
redundant names, and conforming with PEP 8.


Motivation
==========

The normal use case for the `unittest` module is to subclass its
classes, overriding and re-using its functios and methods. This draws
constant attention to the fact that the existing implementation fails
several current Python standards:

* It does not conform to PEP 8 [#PEP-8]_, requiring users to write
  their own non-PEP-8 conformant names when overriding methods, and
  encouraging extensions to further depart from PEP 8.

* It has many synonyms in its API, which goes against the Zen of
  Python [#PEP-20]_ (specifically, that "there should be one, and
  preferably only one, obvious way to do it").


Specification
=============

Remove obsolete names
---------------------

The following module attributes are not documented as part of the API
and are marked as obsolete in the implementation. They will be
removed.

* ``_makeLoader``
* ``getTestCaseNames``
* ``makeSuite``
* ``findTestCases``

Remove redundant names
----------------------

The following attribute names exist only as synonyms for other names.
They are to be removed, leaving only one name for each attribute in
the API.

``TestCase`` attributes
~~~~~~~~~~~~~~~~~~~~~~~

``assert_``
  Use ``assert_true``, or an ``assert`` statement.

``assertEquals``
  Use ``assert_equal``.

``assertNotEquals``
  Use ``assert_not_equal``.

``assertAlmostEquals``
  Use ``assert_almost_equal``.

``assertNotAlmostEquals``
  Use ``assert_not_almost_equal``.

``failIf``
  Use ``assert_false``.

``failUnless``
  Use ``assert_true``.

``failIfAlmostEqual``
  Use ``assert_not_almost_equal``.

``failIfEqual``
  Use ``assert_not_equal``.

``failUnlessAlmostEqual``
  Use ``assert_almost_equal``.
  
``failUnlessEqual``
  Use ``assert_equal``.

``failUnlessRaises``
  Use ``assert_raises``.

Conform API with PEP 8
----------------------

The following names are to be introduced, each replacing an existing
name, to make all names in the module conform with PEP 8 [#PEP-8]_.
Each name is shown with the existing name that it replaces.

Where function parameters are to be renamed also, they are shown.
Where function parameters are not to be renamed, they are elided with
the ellipse ("…") symbol.

Module attributes
~~~~~~~~~~~~~~~~~

``default_test_loader``
  Replaces ``defaultTestLoader``

``TestResult`` attributes
~~~~~~~~~~~~~~~~~~~~~~~~~

``add_error(…)``
  Replaces ``addError(…)``

``add_result(…)``
  Replaces ``addResult(…)``

``add_success(…)``
  Replaces ``addSuccess(…)``

``should_stop``
  Replaces ``shouldStop``

``start_test(…)``
  Replaces ``startTest(…)``

``stop_test(…)``
  Replaces ``stopTest(…)``

``tests_run``
  Replaces ``testsRun``

``was_successful(…)``
  Replaces ``wasSuccessful(…)``

``TestCase`` attributes
~~~~~~~~~~~~~~~~~~~~~~~

``__init__(self, method_name='run_test')``
  Replaces ``__init__(self, methodName='runTest')``

``_test_method_doc``
  Replaces ``_testMethodDoc``

``_test_method_name``
  Replaces ``_testMethodName``

``failure_exception``
  Replaces ``failureException``

``count_test_cases(…)``
  Replaces ``countTestCases(…)``

``default_test_result(…)``
  Replaces ``defaultTestResult(…)``

``assert_true(…)``
  Replaces ``assertTrue(…)``

``assert_false(…)``
  Replaces ``assertFalse(…)``

``assert_almost_equal(…)``
  Replaces ``assertAlmostEqual(…)``

``assert_equal(…)``
  Replaces ``assertEqual(…)``

``assert_not_almost_equal(…)``
  Replaces ``assertNotAlmostEqual(…)``

``assert_not_equal(…)``
  Replaces ``assertNotEqual(…)``

``assert_raises(exc_class, callable_obj, *args, **kwargs)``
  Replaces ``assertRaises(excClass, callableObj, *args, **kwargs)``

``run_test(…)``
  Replaces ``runTest(…)``

``setup(…)``
  Replaces ``setUp(…)``

``short_description(…)``
  Replaces ``shortDescription(…)``

``teardown(…)``
  Replaces ``tearDown(…)``

``FunctionTestCase`` attributes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

``__init__(self, test_func, set_up, tear_down, description)``
  Replaces ``__init__(self, testFunc, setUp, tearDown, description)``

``run_test(…)``
  Replaces ``runTest(…)``

``set_up(…)``
  Replaces ``setUp(…)``

``short_description(…)``
  Replaces ``shortDescription(…)``

``tear_down(…)``
  Replaces ``tearDown(…)``

``TestSuite`` attributes
~~~~~~~~~~~~~~~~~~~~~~~~

``add_test(…)``
  Replaces ``addTest(…)``

``add_tests(…)``
  Replaces ``addTests(…)``

``count_test_cases(…)``
  Replaces ``countTestCases(…)``

``TestLoader`` attributes
~~~~~~~~~~~~~~~~~~~~~~~~~

``sort_test_methods_using``
  Replaces ``sortTestMethodsUsing``

``suite_class``
  Replaces ``suiteClass``

``test_method_prefix``
  Replaces ``testMethodPrefix``

``get_test_case_names(self, test_case_class)``
  Replaces ``getTestCaseNames(self, testCaseClass)``

``load_tests_from_module(…)``
  Replaces ``loadTestsFromModule(…)``

``load_tests_from_name(…)``
  Replaces ``loadTestsFromName(…)``

``load_tests_from_names(…)``
  Replaces ``loadTestsFromNames(…)``

``load_tests_from_test_case(self, test_case_class)``
  Replaces ``loadTestsFromTestCase(self, testCaseClass)``

``_TextTestResult`` attributes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

``show_all``
  Replaces ``showAll``

``add_error(…)``
  Replaces ``addError(…)``

``add_failure(…)``
  Replaces ``addFailure(…)``

``add_success(…)``
  Replaces ``addSuccess(…)``

``get_description(…)``
  Replaces ``getDescription(…)``

``print_error_list(…)``
  Replaces ``printErrorList(…)``

``print_errors(…)``
  Replaces ``printErrors(…)``

``start_test(…)``
  Replaces ``startTest(…)``

``TextTestRunner`` attributes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

``_make_result(…)``
  Replaces ``_makeResult(…)``

``TestProgram`` attributes
~~~~~~~~~~~~~~~~~~~~~~~~~~

``__init__(self, module, default_test, argv, test_runner, test_loader)``
  Replaces ``__init__(self, module, defaultTest, argv, testRunner, testLoader)``

``create_tests(…)``
  Replaces ``createTests(…)``

``parse_args(…)``
  Replaces ``parseArgs(…)``

``run_tests(…)``
  Replaces ``runTests(…)``

``usage_exit(…)``
  Replaces ``usageExit(…)``


Rationale
=========

Redundant names
---------------

The current API, with two or in some cases three different names
referencing exactly the same function, leads to an overbroad and
redundant API that violates PEP 20 [#PEP-20]_ ("there should be one,
and preferably only one, obvious way to do it").

Removal of ``fail*`` names
--------------------------

While there is consensus support to `remove redundant names`_ for the
``TestCase`` test methods, the issue of which set of names should be
retained is controversial (it was several times characterised as
"bike-shedding" [#bikeshed]_ by the BDFL and others).

With good arguments made in favour of each of "retain ``assert*``" and
"retain ``fail*``", this PEP resolves in favour of stated BDFL
preference, and de facto community preference.

Arguments in favour of retaining only the ``assert*`` names:

* BDFL preference: The BDFL has stated [#vanrossum-1]_ a preference
  for the ``assert*`` names.

* Precedent: The Python standard library currently uses the
  ``assert*`` names by a roughly 8:1 majority over the ``fail*``
  names. (Counting unit tests in the py3k tree at 2008-07-15
  [#pitrou-1]_.)

  An ad-hoc sampling of other projects that use `unittest` also
  demonstrates strong preference for use of the ``assert*`` names
  [#bennetts-1]_, [#seaver-1]_.

* Economic: The above precedent indicates a simple economic argument
  [#turnbull-1]_: the majority of tests will not need their statements
  re-phrased, so updating in favour of them will involve less
  disruption and risk of error.

* Positive admonition: The ``assert*`` names state the intent of how
  the code under test *should* behave, while the ``fail*`` names are
  phrased in terms of how the code *should not* behave.

Arguments in favour of retaining only the ``fail*`` names:

* Explicit is better than implicit: The ``fail*`` names state *what
  the function will do* explicitly: fail the test. With the
  ``assert*`` names, the action to be taken is only implicit.

* Avoid false implication: The test methods do not have any necessary
  connection with the built-in ``assert`` statement. Even the
  exception raised, while it defaults to ``AssertionException``, is
  explicitly customisable via the documented ``failure_exception``
  attribute. Choosing the ``fail*`` names avoids the false association
  with either of these.

  It has been argued [#thomas-1]_ that newcomers to `unittest` who
  already know what ``assert`` does can be confused by the behaviour
  of the ``assert*`` names. This confusion does not exist for the
  ``fail*`` names, which don't conflict with existing concepts.

* Avoid name collision: The above confusion with ``assert`` is
  exacerbated by the plain-boolean test using a name of ``assert_``
  (with a trailing underscore) to avoid a name collision with the
  built-in ``assert`` statement. The corresponding ``fail_if`` name
  has no such issue.

PEP 8 names
-----------

Although `unittest` (and its predecessor `PyUnit`) are intended to be
familiar to users of other xUnit interfaces, there is no attempt at
direct API compatibility since the only code that Python's `unittest`
interfaces with is other Python code. The module is in the standard
library and its names should all conform with PEP 8 [#PEP-8]_.

While argument was raised [#hettinger-1]_ over the length of names
resulting from a simple conversion of names to
multi_word_with_underscores, this PEP chooses names that are
consistent in wording with the existing names.

An exception was made in the case of ``setup`` and ``teardown``. The
two-word form of these names was judged [#hettinger-1]_ too cumbersome
compared to the new single-word form.
 

Backwards Compatibility
=======================

The names to be obsoleted should be deprecated and removed according
to the schedule for modules in PEP 4 [#PEP-4]_.

While deprecated, use of the deprecated attributes should raise a
``DeprecationWarning``, with a message stating which replacement name
should be used.


Reference Implementation
========================

None yet.


Copyright
=========

This document is hereby placed in the public domain by its author.


..  [#PEP-4] http://www.python.org/dev/peps/pep-0004
..  [#PEP-8] http://www.python.org/dev/peps/pep-0008
..  [#PEP-20] http://www.python.org/dev/peps/pep-0020
..  [#bikeshed] http://www.catb.org/~esr/jargon/html/B/bikeshedding.html
..  [#vanrossum-1] http://mail.python.org/pipermail/python-dev/2008-April/078485.html
..  [#pitrou-1] http://mail.python.org/pipermail/python-dev/2008-July/081090.html
..  [#bennetts-1] http://mail.python.org/pipermail/python-dev/2008-July/081141.html
..  [#seaver-1] http://mail.python.org/pipermail/python-dev/2008-July/081166.html
..  [#thomas-1] http://mail.python.org/pipermail/python-dev/2008-July/081153.html
..  [#hettinger-1] http://mail.python.org/pipermail/python-dev/2008-July/081107.html
..  [#turnbull-1] http://mail.python.org/pipermail/python-dev/2008-July/081175.html


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