nose2 supports plugins for test collection, selection, observation and reporting – among other things. There are two basic rules for plugins:
Plugin classes must subclass
Plugins may implement any of the methods described in the Hook reference.
Here’s a basic plugin. It doesn’t do anything besides log a message at the start of a test run.
import logging import os from nose2.events import Plugin log = logging.getLogger('nose2.plugins.helloworld') class HelloWorld(Plugin): configSection = 'helloworld' commandLineSwitch = (None, 'hello-world', 'Say hello!') def startTestRun(self, event): log.info('Hello pluginized world!')
To see this plugin in action, save it into an importable module, then
add that module to the
plugins key in the
of a config file loaded by nose2, such as
unittest.cfg. Then run
nose2 --log-level=INFO --hello-world
And you should see the log message before the first dot appears.
As mentioned above, for nose2 to find a plugin, it must be in an
importable module, and the module must be listed under the
key in the
[unittest] section of a config file loaded by nose2:
[unittest] plugins = mypackage.someplugin otherpackage.thatplugin thirdpackage.plugins.metoo
As you can see, plugin modules are listed, one per line. All plugin
classes in those modules will be loaded – but not necessarily
active. Typically plugins do not activate themselves (“register”)
without seeing a command-line flag, or
always-on = True in their
config file section.
nose2 uses argparse for command-line argument parsing. Plugins may enable command-line options that register them as active, or take arguments or flags controlling their operation.
The most basic thing to do is to set the plugin’s
commandLineSwitch attribute, which will automatically add a
command-line flag that registers the plugin.
To add other flags or arguments, you can use the Plugin methods
nose2.events.Plugin.addOption(). If those don’t offer enough
flexibility, you can directly manipulate the argument parser by
self.session.argparse or the plugin option group by
Please note though that the majority of your plugin’s configuration should be done via config file options, not command line options.
Config File Options
Plugins may specify a config file section that holds their
configuration by setting their
configSection attribute. All
plugins, regardless of whether they specify a config section, have a
config attribute that holds a
instance. This will be empty of values if the plugin does not specify
a config section or if no loaded config file includes that section.
Plugins should extract the user’s configuration selections from their
config attribute in their
__init__ methods. Plugins that want to
use nose2’s Sphinx extension to automatically document themselves
must do so.
Config file options may be extracted as strings, ints, booleans or lists.
You should provide reasonable defaults for all config options.
nose2’s plugin API is based on the API in unittest2’s
plugins branch (under-development). Its differs from nose’s
in one major area: what it passes to hooks. Where nose passes a
variety of arguments, nose2 always passes an event. The events are
listed in the Event reference.
Here’s the key thing about that: event attributes are read-write. Unless stated otherwise in the documentation for a hook, you can set a new value for any event attribute, and this will do something. Plugins and nose2 systems will see that new value and either use it instead of what was originally set in the event (example: the reporting stream or test executor), or use it to supplement something they find elsewhere (example: extraTests on a test loading event).
Many hooks give plugins a chance to completely handle events,
bypassing other plugins and any core nose2 operations. To do this, a
event.handled to True and, generally, returns an
appropriate value from the hook method. What is an appropriate value
varies by hook, and some hooks can’t be handled in this way. But
even for hooks where handling the event doesn’t stop all processing,
it will stop subsequently-loaded plugins from seeing the event.
nose2 uses the logging classes from the standard library. To enable users
to view debug messages easily, plugins should use
acquire a logger in the
Writing a plugin that monitors or controls test result output
Implement any of the
report*hook methods, especially if you want to output to the console. If outputting to file or other system, you might implement
Writing a plugin that handles exceptions
If you just want to handle some exceptions as skips or failures instead of errors, see
nose2.plugins.outcomes.Outcomes, which offers a simple way to do that. Otherwise, implement
setTestOutcome()to change test outcomes.
Writing a plugin that adds detail to error reports
Writing a plugin that loads tests from files other than python modules
Writing a plugin that loads tests from python modules
Implement at least
One thing to beware of here is that if you return tests as dynamically-generated test cases, or instances of a testcase class that is defined anywhere but the module being loaded, you must use
nose2.util.transplant_class()to make the test case class appear to have originated in that module. Otherwise, module-level fixtures will not work for that test, and may be ignored entirely for the module if there are no test cases that are or appear to be defined there.
Writing a plugin that prints a report
Writing a plugin that selects or rejects tests