Writing Plugins

nose supports plugins for test collection, selection, observation and reporting. There are two basic rules for plugins:

• Plugin classes should subclass nose.plugins.Plugin.

• Plugins may implement any of the methods described in the class PluginInterface in nose.plugins.base. Please note that this class is for documentary purposes only; plugins may not subclass PluginInterface.

Registering

Important note: the following applies only to the default plugin manager. Other plugin managers may use different means to locate and load plugins.

For nose to find a plugin, it must be part of a package that uses setuptools, and the plugin must be included in the entry points defined in the setup.py for the package:

setup(name='Some plugin',
      ...
      entry_points = {
          'nose.plugins.0.10': [
              'someplugin = someplugin:SomePlugin'
              ]
          },
      ...
      )

Once the package is installed with install or develop, nose will be able to load the plugin.

Defining options

All plugins must implement the methods options(self, parser, env)and configure(self, options, conf). Subclasses of nose.plugins.Plugin that want the standard options should call the superclass methods.

nose uses optparse.OptionParser from the standard library to parse arguments. A plugin's options() method receives a parser instance. It's good form for a plugin to use that instance only to add additional arguments that take only long arguments (--like-this). Most of nose's built-in arguments get their default value from an environment variable.

A plugin's configure() method receives the parsed OptionParser options object, as well as the current config object. Plugins should configure their behavior based on the user-selected settings, and may raise exceptions if the configured behavior is nonsensical.

Logging

nose uses the logging classes from the standard library. To enable users to view debug messages easily, plugins should use logging.getLogger() to acquire a logger in the nose.plugins namespace.

Recipes

• Writing a plugin that monitors or controls test result output

Implement any or all of addError, addFailure, etc., to monitor test results. If you also want to monitor output, implement setOutputStream and keep a reference to the output stream. If you want to prevent the builtin TextTestResult output, implement setOutputSteam and return a dummy stream. The default output will go to the dummy stream, while you send your desired output to the real stream.

Example: examples/html_plugin/htmlplug.py

• Writing a plugin that handles exceptions

Subclass ErrorClassPlugin.

Examples: nose.plugins.deprecated, nose.plugins.skip

• Writing a plugin that adds detail to error reports

Implement formatError and/or formatFailture. The error tuple you return (error class, error message, traceback) will replace the original error tuple.

Examples: nose.plugins.capture, nose.plugins.failuredetail

• Writing a plugin that loads tests from files other than python modules

Implement wantFile and loadTestsFromFile. In wantFile, return True for files that you want to examine for tests. In loadTestsFromFile, for those files, return an iterable containing TestCases (or yield them as you find them; loadTestsFromFile may also be a generator).

Example: nose.plugins.doctests

• Writing a plugin that prints a report

Implement begin if you need to perform setup before testing begins. Implement report and output your report to the provided stream.

Examples: nose.plugins.cover, nose.plugins.prof

• Writing a plugin that selects or rejects tests

Implement any or all want* methods. Return False to reject the test candidate, True to accept it -- which means that the test candidate will pass through the rest of the system, so you must be prepared to load tests from it if tests can't be loaded by the core loader or another plugin -- and None if you don't care.

Examples: nose.plugins.attrib, nose.plugins.doctests, nose.plugins.testid

More Examples

See any builtin plugin or example plugin in the examples directory in the nose source distribution.

Testing Plugins

The plugin interface is well-tested enough so that you can safely unit test your use of its hooks with some level of confidence. However, there is a mixin for unittest.TestCase called PluginTester that's designed to test plugins in their native runtime environment.

Here's a simple example with a do-nothing plugin and a composed suite.

>>> import unittest
>>> from nose.plugins import Plugin, PluginTester
>>> class FooPlugin(Plugin):
...     pass
>>> class TestPluginFoo(PluginTester, unittest.TestCase):
...     activate = '--with-foo'
...     plugins = [FooPlugin()]
...     def test_foo(self):
...         for line in self.output:
...             # i.e. check for patterns
...             pass
...
...         # or check for a line containing ...
...         assert "ValueError" in self.output
...     def makeSuite(self):
...         class TC(unittest.TestCase):
...             def runTest(self):
...                 raise ValueError("I hate foo")
...         return unittest.TestSuite([TC()])
...
>>> res = unittest.TestResult()
>>> case = TestPluginFoo('test_foo')
>>> case(res)
>>> res.errors
[]
>>> res.failures
[]
>>> res.wasSuccessful()
True
>>> res.testsRun
1

And here is a more complex example of testing a plugin that has extra arguments and reads environment variables.

>>> import unittest, os
>>> from nose.plugins import Plugin, PluginTester
>>> class FancyOutputter(Plugin):
...     name = "fancy"
...     def configure(self, options, conf):
...         Plugin.configure(self, options, conf)
...         if not self.enabled:
...             return
...         self.fanciness = 1
...         if options.more_fancy:
...             self.fanciness = 2
...         if 'EVEN_FANCIER' in self.env:
...             self.fanciness = 3
...
...     def options(self, parser, env=os.environ):
...         self.env = env
...         parser.add_option('--more-fancy', action='store_true')
...         Plugin.options(self, parser, env=env)
...
...     def report(self, stream):
...         stream.write("FANCY " * self.fanciness)
...
>>> class TestFancyOutputter(PluginTester, unittest.TestCase):
...     activate = '--with-fancy' # enables the plugin
...     plugins = [FancyOutputter()]
...     args = ['--more-fancy']
...     env = {'EVEN_FANCIER': '1'}
...
...     def test_fancy_output(self):
...         assert "FANCY FANCY FANCY" in self.output, (
...                                         "got: %s" % self.output)
...     def makeSuite(self):
...         class TC(unittest.TestCase):
...             def runTest(self):
...                 raise ValueError("I hate fancy stuff")
...         return unittest.TestSuite([TC()])
...
>>> res = unittest.TestResult()
>>> case = TestFancyOutputter('test_fancy_output')
>>> case(res)
>>> res.errors
[]
>>> res.failures
[]
>>> res.wasSuccessful()
True
>>> res.testsRun
1

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