[Python-Dev] PEP: Consolidating names and classes in the `unittest` module (updated 2008-07-15)

[Ben Finney]

Significant updates are to the preamble (Python-Version field), the
sections "Use new-style classes throughout", "Module attributes", and
a new Rationale section "Removal of ``assert*`` names".


:PEP:               XXX
:Title:             Consolidating names and classes in the `unittest` module
:Version:           0.0
:Last-Modified:     2008-07-15
: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 and classes that constitute
the API of the standard library `unittest` module, with the goal of
removing redundant names, conforming with PEP 8, and eliminating
classic classes.


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 use new-style classes, preventing e.g. straightforward
  use of ``super`` for calling the fixture set-up and tear-down
  methods.

* It does not conform to 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 (specifically, that "there should be one, and preferably only
  one, obvious way to do it").


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

Use new-style classes throughout
--------------------------------

The following classes are currently implemented as classic
("old-style") classes, with no metaclass.

* ``TestResult``
* ``TestCase``
* ``TestSuite``
* ``TestLoader``
* ``_WritelnDecorator``
* ``TextTestRunner``
* ``TestProgram``

The `unittest` module will gain the following attribute, to set the
default metaclass for classes in the module and thus make all classes
in the module part of the new-style type hierarchy::

    __metaclass__ = type

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
~~~~~~~~~~~~~~~~~~~~~~~

* ``assertEqual``
* ``assertEquals``
* ``assertNotEqual``
* ``assertNotEquals``
* ``assertAlmostEqual``
* ``assertAlmostEquals``
* ``assertNotAlmostEqual``
* ``assertNotAlmostEquals``
* ``assertRaises``
* ``assert_``
* ``assertTrue``
* ``assertFalse``

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. 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(…)``

``fail_if(…)``
  Replaces ``failIf(…)``

``fail_if_almost_equal(…)``
  Replaces ``failIfAlmostEqual(…)``

``fail_if_equal(…)``
  Replaces ``failIfEqual(…)``

``fail_unless(…)``
  Replaces ``failUnless(…)``

``fail_unless_almost_equal(…)`` 
  Replaces ``failUnlessAlmostEqual(…)``

``fail_unless_equal(…)``
  Replaces ``failUnlessEqual(…)``

``fail_unless_raises(exc_class, callable_obj, *args, **kwargs)``
  Replaces ``failUnlessRaises(excClass, callableObj, *args, **kwargs)``

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

``set_up(…)``
  Replaces ``setUp(…)``

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

``tear_down(…)``
  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
=========

New-style classes
-----------------

As a standard library module, `unittest` should not define any classic
classes.

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 ("there should be one, and
preferably only one, obvious way to do it").

Removal of ``assert*`` names
----------------------------

There is no overwhelming consensus on whether to remove the
``assert*`` names or the ``fail*`` names; both are in common use. This
proposal argues the ``fail*`` names are slightly superior, for the
following reasons:

* 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.

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.


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

The names to be obsoleted should be deprecated and removed according
to the schedule for modules in 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.


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