[Python-Dev] proto-pep: plugin proposal (for unittest)

[Michael Foord]

Damn, the email was truncated. Probably my fault. The part missed off is:


Not Yet Implemented
===================

Except where noted, everything in this document is already working in 
the prototype. There are a few open issues and things still to be 
implemented.

Certain event attributes should be read only (like extraTests, 
extraNames etc)
because they should only be extended or modified in place instead of being
replaced.

Add an epilogue to the optparse help messages.

A messaging API for plugins that respects verbosity.

The ``startTestRun`` event needs an alternative way of replacing the default
test run machinery without stopping other plugins from executing. It should
only be possible for *one* plugin to use this.

Should the ``onTestFailEvent`` be able to supress raised exceptions? It 
should
also be able to modify the traceback so that bare asserts could be used but
still provide useful diagnostic information. Should this event be fired for
test skips?

Command line options to unittest, like verbosity, should be put into the 
config
data structure so that they are accessible to plugins.

TestFailEvent needs to be fired on failures in setUpClass and 
setUpModule etc

Plugin.register and Plugin.unregister aren't precisely complementary. 
This means
that unregister can only be called once. This may not be an issue.

Plugin.unregister will fail if any events have already been unhooked. 
This can
easily be fixed.

If the merge to unittest in Python 3.2 happens we need to decide which 
of the
example plugins will be included in unittest. (They will probably all remain
in unittest2.)

Custom test outcomes are *not* supported; making interoperating tools or 
plugins
in the presence of custom outcomes can be very hard.

Should unittest2 have a different config file from unittest, so they can be
configured side-by-side? (``unittest2.cfg`` perhaps.) Alternatively the same
config file could be used with a '[unittest2]' section instead of 
'[unittest]'.

Should ``StopTestEvent.timeTaken`` (plus startTime / stopTime etc) 
include the
time for setUp, tearDown and cleanUps? Should this information be available
separately perhaps?

The discovery command line interface has changed a lot and the tests need
reviewing to ensure they still provide full coverage.

Should there be an "excluded-plugins" section in the config files, so 
projects
can prevent incompatible plugins from being loaded?

Should multiline values in config files be merged instead of overriding each
other. (This is effectively what happens for the plugins list.)

Should ``handleFile`` be fired when a test name is specified at the command
line? (This would be 'tricky' as ``handleFile`` will have to be called 
for the
containing module and then the correct name pulled out of the module.)



Additional Changes
==================

Alongside, and in support of, the plugin system a few changes have been 
made to unittest2. These either have no, or very minor, backwards 
compatibility issues. Changes so far are:

TestLoader has a new attribute ``DEFAULT_PATTERN``. This is so that the
regex matching plugin can change the default pattern used for test discovery
when no pattern is explicitly provided.

Command line parsing is all done by optparse, removing the use of 
getopt. This
makes the help messages more consistent but makes the usage messages less
useful in some situations. This can be fixed with the use of the optparse
epilogue.

unit2 (the default test runner) runs test discovery if invoked without 
any arguments.

unit2 can execute tests in filenames as well as module names - so long 
as the
module pointed to by the filename is importable from the current directory.

FunctionTestCase.id() returns 'module.funcname' instead of just funcname.

Added util.formatTraceback, the default way of formatting tracebacks. 
TestCase
has a new formatTraceback method (delegating to util.formatTraceback). 
TestCase
instances can implement formatTraceback to control how the traceback for 
errors
and failures are represented. Useful for test items that don't represent 
Python
tests, for example the pep8 / pyflakes checker and theoretical javascript
test runners such as exist for py.test and nose.

If you specify test names (modules, classes etc) at the command line 
they will
be loaded individually using ``loader.loadTestsFromName`` instead of
collectively with ``loader.loadTestsFromNames``. This enables individual 
names
to be checked to see if they refer to filenames.


References
==========

.. [#] See 
http://bitbucket.org/jpellerin/unittest2/src/tip/unittest2/plugins/attrib.py 
and 
http://bitbucket.org/jpellerin/unittest2/src/tip/unittest2/plugins/errormaster.py
.. [#] 
http://lists.idyll.org/pipermail/testing-in-python/2010-March/002799.html

On 29/07/2010 23:55, Michael Foord wrote:
> Hello all,
>
> My apologies in advance if email mangles whitespace in the code 
> examples. I can reformulate as a PEP if that is deemed useful and this 
> document can be found online at:
>
> http://hg.python.org/unittest2/file/tip/description.txt
>
> (Please excuse errors and omissions - but do feel free to point them 
> out.)
>
> This is a description, and request for feedback, of the unittest 
> plugin system that I am currently prototyping in the plugins branch of 
> unittest2_. My goal is to merge the plugin system back into unittest 
> itself in Python 3.2.
>
> .. _unittest2: http://hg.python.org/unittest2
>
> As part of the prototype I have been implementing some example plugins 
> (in unittest2/plugins/) so I can develop the mechanism against real 
> rather than imagined use cases. Jason Pellerin, creator of nose, has 
> been providing me with feedback and has been trying it out by porting 
> some of the nose plugins to unittest [#]_. He comments on the system 
> "it looks very flexible and clean". ;-)
>
> Example plugins available and included:
>
> * a pep8 and pyflakes checker
> * a debugger plugin that drops you into pdb on test fail / error
> * a doctest loader (looks for doctests in all text files in the project)
> * use a regex for matching files in test discovery instead of a glob
> * growl notifications on test run start and stop
> * filter individual *test methods* using a regex
> * load test functions from modules as well as TestCases
> * integration with the coverage module for coverage reporting
>
> In addition I intend to create a plugin that outputs junit compatible 
> xml from a test run (for integration with tools like the hudson 
> continuous integration server) and a test runner that runs tests in 
> parallel using multiprocessing.
>
> Not all of these will be included in the merge to unittest. Which ones 
> will is still an open question.
>
> I'd like feedback on the proposal, and hopefully approval to port it 
> into unittest after discussion / amendment / completion. In particular 
> I'd like feedback on the basic system, plus which events should be 
> available and what information should be available in them. Note that 
> the system is *not* complete in the prototype. Enough is implemented 
> to get "the general idea" and to formalise the full system. It still 
> needs extensive tests and the extra work in TestProgram makes it 
> abundantly clear that refactoring there is well overdue...
>
> In the details below open questions and todos are noted. I *really* 
> value feedback (but will ignore bikeshedding ;-)
>
> .. note::
>
> Throughout this document I refer to the prototype implementation using 
> names like ``unittest2.events.hooks``. Should this proposal be 
> accepted then the names will live in the unittest package instead of 
> unittest2.
>
> The core classes for the event system live in the current 
> implementation in the ``unittest2.events`` namespace.
>
>
> Abstract
> ========
>
> unittest lacks a standard way of extending it to provide commonly 
> requested functionality, other than subclassing and overriding (and 
> reimplementing) parts of its behaviour. This document describes a 
> plugin system already partially prototyped in unittest2.
>
> Aspects of the plugin system include:
>
> * an events mechanism where handlers can be registered and called 
> during a test run
> * a Plugin class built over the top of this for easy creation of plugins
> * a configuration system for specifying which plugins should be loaded 
> and for configuring individual plugins
> * command line integration
> * the specific set of events and the information / actions available 
> to them
>
> As the plugin system essentially just adds event calls to key places 
> it has few backwards compatibility issues. Unfortunately existing 
> extensions that override the parts of unittest that call these events 
> will not be compatible with plugins that use them. Framework authors 
> who re-implement parts of unittest, for example custom test runners, 
> may want to add calling these events in appropriate places.
>
>
> Rationale
> =========
>
> Why a plugin system for unittest?
>
> unittest is the standard library test framework for Python but in 
> recent years has been eclipsed in functionality by frameworks like 
> nose and py.test. Among the reasons for this is that these frameworks 
> are easier to extend with plugins than unittest. unittest makes itself 
> particularly difficult to extend by using subclassing as its basic 
> extension mechanism. You subclass and override behaviour in its core 
> classes like the loader, runner and result classes.
>
> This means that where you have more than one "extension" working in 
> the same area it is very hard for them to work together. Whilst 
> various extensions to unittest do exist (e.g. testtools, 
> zope.testrunner etc) they don't tend to work well together. In 
> contrast the plugin system makes creating extensions to unittest much 
> simpler and less likely that extensions will clash with each other.
>
> nose itself exists as a large system built over the top of unittest. 
> Extending unittest in this way was very painful for the creators of 
> nose, and every release of Python breaks nose in some way due to 
> changes in unittest. One of the goals of the extension mechanism is to 
> allow nose2 to be a much thinner set of plugins over unittest(2) that 
> is much simpler to maintain [#]_. The early indications are that the 
> proposed system is a good fit for this goal.
>
>
> Low Level Mechanism
> ====================
>
> The basic mechanism is having events fired at various points during a 
> test run. Plugins can register event handler functions that will be 
> called with an event object. Multiple functions may be registered to 
> handle an event and event handlers can also be removed.
>
> Over the top of this is a ``Plugin`` class that simplifies building 
> plugins on top of this mechanism. This is described in a separate 
> section.
>
> The events live on the ``unittest2.events.hooks`` class. Handlers are 
> added using ``+=`` and removed using ``-=``, a syntax borrowed from 
> the .NET system.
>
> For example adding a handler for the ``startTestRun`` event::
>
> from unittest2.events import hooks
>
> def startTestRun(event):
> print 'test run started at %s' % event.startTime
>
> hooks.startTestRun += startTestRun
>
> Handlers are called with an Event object specific to the event. Each 
> event provides different information on its event objects as 
> attributes. For example the attributes available on 
> ``StartTestRunEvent`` objects are:
>
> * ``suite`` - the test suite for the full test run
> * ``runner`` - the test runner
> * ``result`` - the test result
> * ``startTime``
>
> The name of events, whether any should be added or removed, and what 
> information is available on the event objects are all valid topics for 
> discussion. Specific events and the information available to them is 
> covered in a section below.
>
> An example plugin using events directly is the ``doctestloader`` plugin.
>
> Framework authors who re-implement parts of unittest, for example 
> custom test runners, may want to add calling these events in 
> appropriate places. This is very simple. For example the 
> ``pluginsLoaded`` event is fired with a ``PluginsLoadedEvent`` object 
> that is instantiated without parameters::
>
> from unittest2.events import hooks, PluginsLoadedEvent
>
> hooks.pluginsLoaded(PluginsLoadedEvent())
>
>
> Why use event objects and not function parameters?
> --------------------------------------------------
>
> There are several reasons to use event objects instead of function 
> parameters. The *disadvantage* of this is that the information 
> available to an event is not obvious from the signature of a handler. 
> There are several compelling advantages however:
>
> * the signature of all handler functions is identical and therefore 
> easy to remember
>
> * backwards compatibility - new attributes can be added to event 
> objects (and parameters deprecated) without breaking existing plugins. 
> Changing the way a function is called (unless all handlers have a 
> ``**kw`` signature) is much harder.
>
> * several of the events have a lot of information available. This 
> would make the signature of handlers huge. With an event object 
> handlers only need to be aware of attributes they are interested in 
> and ignore information they aren't interested in ("only pay for what 
> you eat").
>
> * some of the attributes are mutable - the event object is shared 
> between all handlers, this would be less obvious if function 
> parameters were used
>
> * calling multiple handlers and still returning a value (see the 
> handled pattern below)
>
>
> The handled pattern
> --------------------
>
> Several events can be used to *override* the default behaviour. For 
> example the 'matchregexp' plugin uses the ``matchPath`` event to 
> replace the default way of matching files for loading as tests during 
> test discovery. The handler signals that it is handling this event, 
> and the default implementation should not be run, by setting 
> ``event.handled = True``::
>
> def matchRegexp(event):
> pattern = event.pattern
> name = event.name
> event.handled = True
> path = event.path
> if matchFullPath:
> return re.match(pattern, path)
> return re.match(pattern, name)
>
> Where the default implementation returns a value, for example creating 
> a test suite, or in the case of ``matchPath`` deciding if a path 
> matches a file that should be loaded as a test, the handler can return 
> a result.
>
> If an event sets handled on an event then no more handlers will be 
> called for that event. Which events can be handled, and which not, is 
> discussed in the events section.
>
>
> The Plugin Class
> ================
>
> A sometimes-more-convenient way of creating plugins is to subclass the 
> ``unittest2.events.Plugin`` class. By default subclassing ``Plugin`` 
> will auto-instantiate the plugin and store the instance in a list of 
> loaded plugins.
>
> Each plugin has a ``register()`` method that auto-hooks up all methods 
> whose names correspond to events. Plugin classes may also provide 
> ``configSection`` and ``commandLineSwitch`` class attributes which 
> simplifies enabling the plugin through the command line and making 
> available a section from the configuration file(s).
>
> A simple plugin using this is the 'debugger' plugin that starts 
> ``pdb`` when the ``onTestFail`` event fires::
>
> from unittest2.events import Plugin
>
> import pdb
> import sys
>
> class Debugger(Plugin):
>
> configSection = 'debugger'
> commandLineSwitch = ('D', 'debugger', 'Enter pdb on test fail or error')
>
> def __init__(self):
> self.errorsOnly = self.config.as_bool('errors-only', default=False)
>
> def onTestFail(self, event):
> value, tb = event.exc_info[1:]
> test = event.test
> if self.errorsOnly and isinstance(value, test.failureException):
> return
> original = sys.stdout
> sys.stdout = sys.__stdout__
> try:
> pdb.post_mortem(tb)
> finally:
> sys.stdout = original
>
> A plugin that doesn't want to be auto-instantiated (for example a base 
> class used for several plugins) can set ``autoCreate = False`` as a 
> class attribute. (This attribute is only looked for on the class 
> directly and so isn't inherited by subclasses.) If a plugin is 
> auto-instantiated then the instance will be set as the ``instance`` 
> attribute on the plugin class.
>
> ``configSection`` and ``commandLineSwitch`` are described in the 
> `configuration system`_ and `command line integration`_ sections.
>
> Plugin instances also have an ``unregister`` method that unhooks all 
> events. It doesn't exactly correspond to the ``register`` method (it 
> undoes some of the work done when a plugin is instantiated) and so can 
> only be called once.
>
> Plugins to be loaded are specified in configuration files. For 
> frameworks not using the unittest test runner and configuration system 
> APIs for loading plugins are available in the form of the 
> ``loadPlugins`` function (which uses the configuration system to load 
> plugins) and ``loadPlugin`` which loads an individual plugin by module 
> name. Loading plugins just means importing the module containing the 
> plugin.
>
>
>
> Configuration system
> ====================
>
> By default the unittest2 test runner (triggered by the unit2 script or 
> for unittest ``python -m unittest``) loads two configuration files to 
> determine which plugins to load.
>
> A user configuration file, ~/unittest.cfg (alternative name and 
> location would be possible), can specify plugins that will always be 
> loaded. A per-project configuration file, unittest.cfg which should be 
> located in the current directory when unit2 is launched, can specify 
> plugins for individual projects.
>
> To support this system several command line options have been added to 
> the test runner::
>
> --config=CONFIGLOCATIONS
> Specify local config file location
> --no-user-config Don't use user config file
> --no-plugins Disable all plugins
>
> Several config files can be specified using ``--config``. If the user 
> config is being loaded then it will be loaded first (if it exists), 
> followed by the project config (if it exists) *or* any config files 
> specified by ``--config``. ``--config`` can point to specific files, 
> or to a directory containing a ``unittest.cfg``.
>
> Config files loaded later are merged into already loaded ones. Where a 
> *key* is in both the later key overrides the earlier one. Where a 
> section is in both but with different keys they are merged. (The 
> exception to keys overriding is the 'plugins' key in the unittest 
> section - these are combined to create a full list of plugins. Perhaps 
> multiline values in config files could also be merged?)
>
> plugins to be loaded are specified in the ``plugins`` key of the 
> ``unittest`` section::
>
> [unittest]
> plugins =
> unittest2.plugins.checker
> unittest2.plugins.doctestloader
> unittest2.plugins.matchregexp
> unittest2.plugins.moduleloading
> unittest2.plugins.debugger
> unittest2.plugins.testcoverage
> unittest2.plugins.growl
> unittest2.plugins.filtertests
>
> The plugins are simply module names. They either hook themselves up 
> manually on import or are created by virtue of subclassing ``Plugin``. 
> A list of all loaded plugins is available as 
> ``unittest2.events.loadedPlugins`` (a list of strings).
>
> For accessing config values there is a ``getConfig(sectionName=None)`` 
> function. By default it returns the whole config data-structure but it 
> an also return individual sections by name. If the section doesn't 
> exist an empty section will be returned. The config data-structure is 
> not read-only but there is no mechanism for persisting changes.
>
> The config is a dictionary of ``Section`` objects, where a section is 
> a dictionary subclass with some convenience methods for accessing 
> values::
>
> section = getConfig(sectionName)
>
> integer = section.as_int('foo', default=3)
> number = section.as_float('bar', default=0.0)
>
> # as_list returns a list with empty lines and comment lines removed
> items = section.as_list('items', default=[])
>
> # as_bool allows 'true', '1', 'on', 'yes' for True (matched 
> case-insensitively) and
> # 'false', 'off', '0', 'no', '' for False
> value = section.as_bool('value', default=True)
>
> If a plugin specifies a ``configSection`` as a class attribute then 
> that section will be fetched and set as the ``config`` attribute on 
> instances.
>
> By convention plugins should use the 'always-on' key in their config 
> section to specify that the plugin should be switched on by default. 
> If 'always-on' exists and is set to 'True' then the ``register()`` 
> method will be called on the plugin to hook up all events. If you 
> don't want a plugin to be auto-registered you should fetch the config 
> section yourself rather than using ``configSection``.
>
> If the plugin is configured to be 'always-on', and is auto-registered, 
> then it doesn't need a command line switch to turn it on (although it 
> may add other command line switches or options) and 
> ``commandLineSwitch`` will be ignored.
>
>
> Command Line Interface
> ======================
>
> Plugins may add command line options, either switches with a callback 
> function or options that take values and will be added to a list. 
> There are two functions that do this: ``unittest2.events.addOption`` 
> and ``unittest2.events.addDiscoveryOption``. Some of the events are 
> only applicable to test discovery (``matchPath`` is the only one 
> currently I think), options that use these events should use 
> ``addDiscoveryOption`` which will only be used if test discovery is 
> invoked.
>
> Both functions have the same signature::
>
> addDiscoveryOption(callback, opt=None, longOpt=None, help=None)
>
> addOption(plugin.method, 'X', '--extreme', 'Run tests in extreme mode')
>
> * ``callback`` is a callback function (taking no arguments) to be 
> invoked if the option is on *or* a list indicating that this is an 
> option that takes arguments, values passed in at the command line will 
> be added to the list
> * ``opt`` is a short option for the command (or None) not including 
> the leading '-'
> * ``longopt`` a long option for the command (or None) not including 
> the leading '--'
> * ``help`` is optional help text for the option, to be displayed by 
> ``unit2 -h``
>
> Lowercase short options are reserved for use by unittest2 internally. 
> Plugins may only add uppercase short options.
>
> If a plugin needs a simple command line switch (on/off) then it can 
> set the ``commandLineSwitch`` class attribute to a tuple of ``(opt, 
> longOpt, help)``. The ``register()`` method will be used as the 
> callback function, automatically hooking the plugin up to events if it 
> is switched on.
>
>
> The Events
> ==========
>
> This section details the events implemented so far, the order they are 
> called in, what attributes are available on the event objects, whether 
> the event is 'handleable' (and what that means for the event), plus 
> the intended use case for the event.
>
> Events in rough order are:
>
> * ``pluginsLoaded``
> * ``handleFile``
> * ``matchPath``
> * ``loadTestsFromNames``
> * ``loadTestsFromName``
> * ``loadTestsFromModule``
> * ``loadTestsFromTestCase``
> * ``getTestCaseNames``
> * ``runnerCreated``
> * ``startTestRun``
> * ``startTest``
> * ``onTestFail``
> * ``stopTest``
> * ``stopTestRun``
>
>
> pluginsLoaded
> -------------
>
> This event is useful for plugin initialisation. It is fired after all 
> plugins have been loaded, the config file has been read and command 
> line options processed.
>
> The ``PluginsLoadedEvent`` has one attribute: ``loadedPlugins`` which 
> is a list of strings referring to all plugin modules that have been 
> loaded.
>
>
> handleFile
> ----------
>
> This event is fired when a file is looked at in test discovery or a 
> *filename* is passed at the command line. It can be used for loading 
> tests from non-Python files, like doctests from text files, or adding 
> tests for a file like pep8 and pyflakes checks.
>
> A ``HandleFileEvent`` object has the following attributes:
>
> * ``extraTests`` - a list, extend this with tests to *add* tests that 
> will be loaded from this file without preventing the default test loading
> * ``name`` - the name of the file
> * ``path`` - the full path of the file being looked at
> * ``loader`` - the ``TestLoader`` in use
> * ``pattern`` - the pattern being used to match files, or None if not 
> called during test discovery
> * ``top_level_directory`` - the top level directory of the project 
> tests are being loaded from, or the current working directory if not 
> called during test discovery
>
> This event *can* be handled. If it is handled then the handler should 
> return a test suite or None. Returning None means no tests will be 
> loaded from this file. If any plugin has created any ``extraTests`` 
> then these will be used even if a handler handles the event and 
> returns None.
>
> If this event is not handled then it will be matched against the 
> pattern (test discovery only) and either be rejected or go through for 
> standard test loading.
>
>
> matchPath
> ---------
>
> ``matchPath`` is called to determine if a file should be loaded as a 
> test module. This event only fires during test discovery.
>
> ``matchPath`` is only fired if the filename can be converted to a 
> valid python module name, this is because tests are loaded by 
> importing. If you want to load tests from files whose paths don't 
> translate to valid python identifiers then you should use 
> ``handleFile`` instead.
>
> A ``MatchPathEvent`` has the following attributes:
>
> * ``path`` - full path to the file
> * ``name`` - filename only
> * ``pattern`` - pattern being used for discovery
>
> This event *can* be handled. If it is handled then the handler should 
> return True or False to indicate whether or not test loading should be 
> attempted from this file. If this event is not handled then the 
> pattern supplied to test discovery will be used as a glob pattern to 
> match the filename.
>
>
> loadTestsFromNames
> ------------------
>
> This event is fired when ``TestLoader.loadTestsFromNames`` is called.
>
> Attributes on the ``LoadFromNamesEvent`` object are:
>
> * ``loader`` - the test loader
> * ``names`` - a list of the names being loaded
> * ``module`` - the module passed to ``loader.loadTestsFromNames(...)``
> * ``extraTests`` - a list of extra tests to be added to the suites 
> loaded from the names
>
> This event can be handled. If it is handled then the handler should 
> return a list of suites or None. Returning None means no tests will be 
> loaded from these names. If any plugin has created any ``extraTests`` 
> then these will be used even if a handler handles the event and 
> returns None.
>
> If this event is not handled then ``loader.loadTestFromName`` will be 
> called for each name to build up the list of suites.
>
>
> loadTestsFromName
> -----------------
>
> This event is fired when ``TestLoader.loadTestsFromName`` is called.
>
> Attributes on the ``LoadFromNameEvent`` object are:
>
> * ``loader`` - the test loader
> * ``name`` - the name being loaded
> * ``module`` - the module passed to ``loader.loadTestsFromName(...)``
> * ``extraTests`` - a suite of extra tests to be added to the suite 
> loaded from the name
>
> This event can be handled. If it is handled then the handler should 
> return a TestSuite or None. Returning None means no tests will be 
> loaded from this name. If any plugin has created any ``extraTests`` 
> then these will be used even if a handler handles the event and 
> returns None.
>
> If the event is not handled then each name will be resolved and tests 
> loaded from it, which may mean calling ``loader.loadTestsFromModule`` 
> or ``loader.loadTestsFromTestCase``.
>
>
>
> loadTestsFromModule
> -------------------
>
> This event is fired when ``TestLoader.loadTestsFromModule`` is called. 
> It can be used to customise the loading of tests from a module, for 
> example loading tests from functions as well as from TestCase classes.
>
> Attributes on the ``LoadFromModuleEvent`` object are:
>
> * ``loader`` - the test loader
> * ``module`` - the module object tests
> * ``extraTests`` - a suite of extra tests to be added to the suite 
> loaded from the module
>
> This event can be handled. If it is handled then the handler should 
> return a TestSuite or None. Returning None means no tests will be 
> loaded from this module. If any plugin has created any ``extraTests`` 
> then these will be used even if a handler handles the event and 
> returns None.
>
> If the event is not handled then ``loader.loadTestsFromTestCase`` will 
> be called for every TestCase in the module.
>
> Event if the event is handled, if the module defines a ``load_tests`` 
> function then it *will* be called for the module. This removes the 
> responsibility for implementing the ``load_tests`` protocol from 
> plugin authors.
>
>
> loadTestsFromTestCase
> ---------------------
>
> This event is fired when ``TestLoader.loadTestsFromTestCase`` is 
> called. It could be used to customise the loading of tests from a 
> TestCase, for example loading tests with an alternative prefix or 
> created generative / parameterized tests.
>
> Attributes on the ``LoadFromTestCaseEvent`` object are:
>
> * ``loader`` - the test loader
> * ``testCase`` - the test case class being loaded
> * ``extraTests`` - a suite of extra tests to be added to the suite 
> loaded from the TestCase
>
> This event can be handled. If it is handled then the handler should 
> return a TestSuite or None. Returning None means no tests will be 
> loaded from this module. If any plugin has created any ``extraTests`` 
> then these will be used even if a handler handles the event and 
> returns None
>
> If the event is not handled then ``loader.getTestCaseNames`` will be 
> called to get method names from the test case and a suite will be 
> created by instantiating the TestCase class with each name it returns.
>
>
> getTestCaseNames
> ----------------
>
> This event is fired when ``TestLoader.getTestCaseNames`` is called. It 
> could be used to customise the method names used to load tests from a 
> TestCase, for example loading tests with an alternative prefix from 
> the default or filtering for specific names.
>
> Attributes on the ``GetTestCaseNamesEvent`` object are:
>
> * ``loader`` - the test loader
> * ``testCase`` - the test case class that tests are being loaded from
> * ``testMethodPrefix`` - set to None, modify this attribute to 
> *change* the prefix being used for this class
> * ``extraNames`` - a list of extra names to use for this test case as 
> well as the default ones
> * ``excludedNames`` - a list of names to exclude from loading from 
> this class
>
> This event can be handled. If it is handled it should return a list of 
> strings. Note that if this event returns an empty list (or None which 
> will be replaced with an empty list then ``loadTestsFromTestCase`` 
> will still check to see if the TestCase has a ``runTest`` method.
>
> Even if the event is handled ``extraNames`` will still be added to the 
> list, however *excludedNames`` won't be removed as they are filtered 
> out by the default implementation which looks for all attributes that 
> are methods (or callable) whose name begins with 
> ``loader.testMethodPrefix`` (or ``event.testMethodPrefix`` if that is 
> set) and aren't in the list of excluded names (converted to a set 
> first for efficient lookup).
>
> The list of names will also be sorted using 
> ``loader.sortTestMethodsUsing``.
>
>
> runnerCreated
> -------------
>
> This event is fired when the ``TextTestRunner`` is instantiated. It 
> can be used to customize the test runner, for example replace the 
> stream and result class, without needing to write a custom test 
> harness. This should allow the default test runner script (``unit2`` 
> or ``python -m untitest``) to be suitable for a greater range of 
> projects. Projects that want to use custom test reporting should be 
> able to do it through a plugin rather than having to rebuild the 
> runner and result machinery, which also requires writing custom test 
> collection too.
>
> The ``RunnerCreatedEvent`` object only has one attribute; ``runner`` 
> which is the runner instance.
>
>
> startTestRun
> ------------
>
> This event is fired when the test run is started. This is used, for 
> example, by the growl notifier that displays a growl notification when 
> a test run begins. It can also be used for filtering tests after they 
> have all been loaded or for taking over the test run machinery 
> altogether, for distributed testing for example.
>
> The ``StartTestRunEvent`` object has the following attributes:
>
> * ``test`` - the full suite of all tests to be run (may be modified in 
> place)
> * ``result`` - the result object
> * ``startTime`` - the time the test run started
>
> Currently this event can be handled. This prevents the normal test run 
> from executing, allowing an alternative implementation, but the return 
> value is unused. Handling this event (as with handling any event) 
> prevents other plugins from executing. This means that the it wouldn't 
> be possible to safely combine a distributed test runner with a plugin 
> that filters the suite. Fixing this issue is one of the open issues 
> with the plugin system.
>
>
> startTest
> ---------
>
> This event is fired immediately before a test is executed (inside 
> ``TestCase.run(...)``).
>
> The ``StartTestEvent`` object has the following attributes:
>
> * ``test`` - the test to be run
> * ``result`` - the result object
> * ``startTime`` - the time the test starts execution
>
> This event cannot be handled.
>
>
> onTestFail
> ----------
>
> This event is fired when a test setUp, a test, a tearDown or a cleanUp 
> fails or errors. It is currently used by the debugger plugin. It is 
> *not* currently called for 'internal' unittest exceptions like 
> ``SkipTest`` or expected failures and unexpected successes.
>
> Attributes on the ``TestFailEvent`` are:
>
> * ``test`` - the test
> * ``result`` - the result
> * ``exc_info`` - the result of ``sys.exc_info()`` after the error / fail
> * ``when`` - one of 'setUp', 'call', 'tearDown', or 'cleanUp'
>
> This event cannot be handled. Should this event be able to suppress 
> raised exceptions? It should also be able to modify the traceback so 
> that bare asserts could be used but still provide useful diagnostic 
> information. Should this event be fired for test skips?
>
>
> stopTest
> --------
>
> This event is fired when a test execution is completed. It includes a 
> great deal of information about the test and could be used to 
> completely replace test reporting, making the test result potentially 
> obsolete. It will be used by the junit-xml plugin to generate the xml 
> reports describing the test run.
>
> If there are errors during a tearDown or clean up functions then this 
> event may be fired several times for a test. For each call the 
> ``stage`` will be different, although there could be several errors 
> during clean up functions.
>
> Attributes on the ``StopTestEvent`` are:
>
> * ``test`` - the test
> * ``result`` - the result
> * ``exc_info`` - the result of ``sys.exc_info()`` after an error / 
> fail or None for success
> * ``stopTime``- time the test stopped, including tear down and clean 
> up functions
> * ``timeTaken`` - total time for test execution from setUp to clean up 
> functions
> * ``stage`` - one of setUp, call, tearDown, cleanUp, or None for success
> * ``outcome`` - one of passed, failed, error, skipped, 
> unexpectedSuccess, expectedFailure
>
> The outcomes all correspond to an attribute that will be set to True 
> or False depending on outcome:
>
> * ``passed``
> * ``failed``
> * ``error``
> * ``skipped``
> * ``unexpectedSuccess``
> * ``expectedFailure``
>
> In addition there is a ``skipReason`` that will be None unless the 
> test was skipped, in which case it will be a string containing the 
> reason.
>
> This event cannot be handled.
>
>
> stopTestRun
> -----------
>
> This event is fired when the test run completes. It is useful for 
> reporting tools.
>
> The ``StopTestRunEvent`` event objects have the following attributes:
>
> * ``runner`` - the test runner
> * ``result`` - the test result
> * ``stopTime`` - the time the test run completes
> * ``timeTaken`` - total time taken by the test run
> _______________________________________________
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>


-- 
http://www.ironpythoninaction.com/
http://www.voidspace.org.uk/blog

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