Working with plugins and conftest files

pytest implements all aspects of configuration, collection, running and reporting by calling well specified hooks. Virtually any Python module can be registered as a plugin. It can implement any number of hook functions (usually two or three) which all have a pytest_ prefix, making hook functions easy to distinguish and find. There are three basic location types:

conftest.py: local per-directory plugins

local conftest.py plugins contain directory-specific hook implementations. Session and test running activities will invoke all hooks defined in conftest.py files closer to the root of the filesystem. Example: Assume the following layout and content of files:

a/conftest.py:
    def pytest_runtest_setup(item):
        # called for running each test in 'a' directory
        print ("setting up", item)

a/test_in_subdir.py:
    def test_sub():
        pass

test_flat.py:
    def test_flat():
        pass

Here is how you might run it:

py.test test_flat.py   # will not show "setting up"
py.test a/test_sub.py  # will show "setting up"

Note

If you have conftest.py files which do not reside in a python package directory (i.e. one containing an __init__.py) then “import conftest” can be ambiguous because there might be other conftest.py files as well on your PYTHONPATH or sys.path. It is thus good practise for projects to either put conftest.py under a package scope or to never import anything from a conftest.py file.

Installing External Plugins / Searching

Installing a plugin happens through any usual Python installation tool, for example:

pip install pytest-NAME
pip uninstall pytest-NAME

If a plugin is installed, pytest automatically finds and integrates it, there is no need to activate it. We have a page listing all 3rd party plugins and their status against the latest py.test version and here is a little annotated list for some popular plugins:

  • pytest-django: write tests for django apps, using pytest integration.
  • pytest-twisted: write tests for twisted apps, starting a reactor and processing deferreds from test functions.
  • pytest-capturelog: to capture and assert about messages from the logging module
  • pytest-cov: coverage reporting, compatible with distributed testing
  • pytest-xdist: to distribute tests to CPUs and remote hosts, to run in boxed mode which allows to survive segmentation faults, to run in looponfailing mode, automatically re-running failing tests on file changes, see also xdist: pytest distributed testing plugin
  • pytest-instafail: to report failures while the test run is happening.
  • pytest-bdd and pytest-konira to write tests using behaviour-driven testing.
  • pytest-timeout: to timeout tests based on function marks or global definitions.
  • pytest-cache: to interactively re-run failing tests and help other plugins to store test run information across invocations.
  • pytest-pep8: a --pep8 option to enable PEP8 compliance checking.
  • oejskit: a plugin to run javascript unittests in life browsers

To see a complete list of all plugins with their latest testing status against different py.test and Python versions, please visit pytest-plugs.

You may also discover more plugins through a pytest- pypi.python.org search.

Writing a plugin by looking at examples

If you want to write a plugin, there are many real-life examples you can copy from:

All of these plugins implement the documented well specified hooks to extend and add functionality.

Making your plugin installable by others

If you want to make your plugin externally available, you may define a so-called entry point for your distribution so that pytest finds your plugin module. Entry points are a feature that is provided by setuptools or Distribute. pytest looks up the pytest11 entrypoint to discover its plugins and you can thus make your plugin available by defining it in your setuptools/distribute-based setup-invocation:

# sample ./setup.py file
from setuptools import setup

setup(
    name="myproject",
    packages = ['myproject']

    # the following makes a plugin available to pytest
    entry_points = {
        'pytest11': [
            'name_of_plugin = myproject.pluginmodule',
        ]
    },
)

If a package is installed this way, pytest will load myproject.pluginmodule as a plugin which can define well specified hooks.

Plugin discovery order at tool startup

pytest loads plugin modules at tool startup in the following way:

  • by loading all builtin plugins

  • by loading all plugins registered through setuptools entry points.

  • by pre-scanning the command line for the -p name option and loading the specified plugin before actual command line parsing.

  • by loading all conftest.py files as inferred by the command line invocation:

    • if no test paths are specified use current dir as a test path
    • if exists, load conftest.py and test*/conftest.py relative to the directory part of the first test path.

    Note that pytest does not find conftest.py files in deeper nested sub directories at tool startup. It is usually a good idea to keep your conftest.py file in the top level test or project root directory.

  • by recursively loading all plugins specified by the pytest_plugins variable in conftest.py files

Requiring/Loading plugins in a test module or conftest file

You can require plugins in a test module or a conftest file like this:

pytest_plugins = "name1", "name2",

When the test module or conftest plugin is loaded the specified plugins will be loaded as well. You can also use dotted path like this:

pytest_plugins = "myapp.testsupport.myplugin"

which will import the specified module as a pytest plugin.

Accessing another plugin by name

If a plugin wants to collaborate with code from another plugin it can obtain a reference through the plugin manager like this:

plugin = config.pluginmanager.getplugin("name_of_plugin")

If you want to look at the names of existing plugins, use the --traceconfig option.

Finding out which plugins are active

If you want to find out which plugins are active in your environment you can type:

py.test --traceconfig

and will get an extended test header which shows activated plugins and their names. It will also print local plugins aka conftest.py files when they are loaded.

Deactivating / unregistering a plugin by name

You can prevent plugins from loading or unregister them:

py.test -p no:NAME

This means that any subsequent try to activate/load the named plugin will it already existing. See Finding out which plugins are active for how to obtain the name of a plugin.

pytest default plugin reference

You can find the source code for the following plugins in the pytest repository.

_pytest.assertion support for presenting detailed information in failing assertions.
_pytest.capture per-test stdout/stderr capturing mechanism.
_pytest.config command line options, ini-file and conftest.py processing.
_pytest.doctest discover and run doctests in modules and test files.
_pytest.genscript generate a single-file self-contained version of pytest
_pytest.helpconfig version info, help messages, tracing configuration.
_pytest.junitxml report test results in JUnit-XML format, for use with Hudson and build integration servers.
_pytest.mark generic mechanism for marking and selecting python functions.
_pytest.monkeypatch monkeypatching and mocking functionality.
_pytest.nose run test suites written for nose.
_pytest.pastebin submit failure or test session information to a pastebin service.
_pytest.pdb interactive debugging with PDB, the Python Debugger.
_pytest.pytester (disabled by default) support for testing pytest and pytest plugins.
_pytest.python Python test discovery, setup and run of test functions.
_pytest.recwarn recording warnings during test function execution.
_pytest.resultlog log machine-parseable test session result information in a plain
_pytest.runner basic collect and runtest protocol implementations
_pytest.main core implementation of testing process: init, session, runtest loop.
_pytest.skipping support for skip/xfail functions and markers.
_pytest.terminal terminal reporting of the full testing process.
_pytest.tmpdir support for providing temporary directories to test functions.
_pytest.unittest discovery and running of std-library “unittest” style tests.

pytest hook reference

Hook specification and validation

pytest calls hook functions to implement initialization, running, test execution and reporting. When pytest loads a plugin it validates that each hook function conforms to its respective hook specification. Each hook function name and its argument names need to match a hook specification. However, a hook function may accept fewer parameters by simply not specifying them. If you mistype argument names or the hook name itself you get an error showing the available arguments.

Initialization, command line and configuration hooks

pytest_load_initial_conftests(args, early_config, parser)[source]

implements the loading of initial conftest files ahead of command line option parsing.

pytest_cmdline_preparse(config, args)[source]

(deprecated) modify command line arguments before option parsing.

pytest_cmdline_parse(pluginmanager, args)[source]

return initialized config object, parsing the specified args.

pytest_namespace()[source]

return dict of name->object to be made globally available in the pytest namespace. This hook is called before command line options are parsed.

pytest_addoption(parser)[source]

register argparse-style options and ini-style config values.

This function must be implemented in a plugin and is called once at the beginning of a test run.

Parameters:parser – To add command line options, call parser.addoption(...). To add ini-file values call parser.addini(...).

Options can later be accessed through the config object, respectively:

The config object is passed around on many internal objects via the .config attribute or can be retrieved as the pytestconfig fixture or accessed via (deprecated) pytest.config.

pytest_cmdline_main(config)[source]

called for performing the main command line action. The default implementation will invoke the configure hooks and runtest_mainloop.

pytest_configure(config)[source]

called after command line options have been parsed and all plugins and initial conftest files been loaded.

pytest_unconfigure(config)[source]

called before test process is exited.

Generic “runtest” hooks

All runtest related hooks receive a pytest.Item object.

pytest_runtest_protocol(item, nextitem)[source]

implements the runtest_setup/call/teardown protocol for the given test item, including capturing exceptions and calling reporting hooks.

Parameters:
  • item – test item for which the runtest protocol is performed.
  • nextitem – the scheduled-to-be-next test item (or None if this is the end my friend). This argument is passed on to pytest_runtest_teardown().
Return boolean:

True if no further hook implementations should be invoked.

pytest_runtest_setup(item)[source]

called before pytest_runtest_call(item).

pytest_runtest_call(item)[source]

called to execute the test item.

pytest_runtest_teardown(item, nextitem)[source]

called after pytest_runtest_call.

Parameters:nextitem – the scheduled-to-be-next test item (None if no further test item is scheduled). This argument can be used to perform exact teardowns, i.e. calling just enough finalizers so that nextitem only needs to call setup-functions.
pytest_runtest_makereport(item, call)[source]

return a _pytest.runner.TestReport object for the given pytest.Item and _pytest.runner.CallInfo.

For deeper understanding you may look at the default implementation of these hooks in _pytest.runner and maybe also in _pytest.pdb which interacts with _pytest.capture and its input/output capturing in order to immediately drop into interactive debugging when a test failure occurs.

The _pytest.terminal reported specifically uses the reporting hook to print information about a test run.

Collection hooks

pytest calls the following hooks for collecting files and directories:

pytest_ignore_collect(path, config)[source]

return True to prevent considering this path for collection. This hook is consulted for all files and directories prior to calling more specific hooks.

pytest_collect_directory(path, parent)[source]

called before traversing a directory for collection files.

pytest_collect_file(path, parent)[source]

return collection Node or None for the given path. Any new node needs to have the specified parent as a parent.

For influencing the collection of objects in Python modules you can use the following hook:

pytest_pycollect_makeitem(collector, name, obj)[source]

return custom item/collector for a python object in a module, or None.

pytest_generate_tests(metafunc)[source]

generate (multiple) parametrized calls to a test function.

After collection is complete, you can modify the order of items, delete or otherwise amend the test items:

pytest_collection_modifyitems(session, config, items)[source]

called after collection has been performed, may filter or re-order the items in-place.

Reporting hooks

Session related reporting hooks:

pytest_collectstart(collector)[source]

collector starts collecting.

pytest_itemcollected(item)[source]

we just collected a test item.

pytest_collectreport(report)[source]

collector finished collecting.

pytest_deselected(items)[source]

called for test items deselected by keyword.

And here is the central hook for reporting about test execution:

pytest_runtest_logreport(report)[source]

process a test setup/call/teardown report relating to the respective phase of executing a test.

Debugging/Interaction hooks

There are few hooks which can be used for special reporting or interaction with exceptions:

pytest_internalerror(excrepr, excinfo)[source]

called for internal errors.

pytest_keyboard_interrupt(excinfo)[source]

called for keyboard interrupt.

pytest_exception_interact(node, call, report)[source]

(experimental, new in 2.4) called when an exception was raised which can potentially be interactively handled.

This hook is only called if an exception was raised that is not an internal exception like “skip.Exception”.

Reference of objects involved in hooks

class Config[source]

access to configuration values, pluginmanager and plugin hooks.

option = None

access to command line option as attributes. (deprecated), use getoption() instead

pluginmanager = None

a pluginmanager instance

warn(code, message)[source]

generate a warning for this test session.

classmethod fromdictargs(option_dict, args)[source]

constructor useable for subprocesses.

addinivalue_line(name, line)[source]

add a line to an ini-file option. The option must have been declared but might not yet be set in which case the line becomes the the first line in its value.

getini(name)[source]

return configuration value from an ini file. If the specified name hasn’t been registered through a prior parser.addini call (usually from a plugin), a ValueError is raised.

getoption(name, default=<NOTSET>, skip=False)[source]

return command line option value.

Parameters:
  • name – name of the option. You may also specify the literal --OPT option instead of the “dest” option name.
  • default – default value if no option of that name exists.
  • skip – if True raise pytest.skip if option does not exists or has a None value.
getvalue(name, path=None)[source]

(deprecated, use getoption())

getvalueorskip(name, path=None)[source]

(deprecated, use getoption(skip=True))

class Parser[source]

Parser for command line arguments and ini-file values.

getgroup(name, description='', after=None)[source]

get (or create) a named option Group.

Name:name of the option group.
Description:long description for –help output.
After:name of other group, used for ordering –help output.

The returned group object has an addoption method with the same signature as parser.addoption but will be shown in the respective group in the output of pytest. --help.

addoption(*opts, **attrs)[source]

register a command line option.

Opts:option names, can be short or long options.
Attrs:same attributes which the add_option() function of the argparse library accepts.

After command line parsing options are available on the pytest config object via config.option.NAME where NAME is usually set by passing a dest attribute, for example addoption("--long", dest="NAME", ...).

addini(name, help, type=None, default=None)[source]

register an ini-file option.

Name:name of the ini-variable
Type:type of the variable, can be pathlist, args or linelist.
Default:default value if no ini-file option exists but is queried.

The value of ini-variables can be retrieved via a call to config.getini(name).

class Node[source]

base class for Collector and Item the test collection tree. Collector subclasses have children, Items are terminal nodes.

name = None

a unique name within the scope of the parent node

parent = None

the parent collector node.

config = None

the pytest config object

session = None

the session this node is part of

fspath = None

filesystem path where this node was collected from (can be None)

keywords = None

keywords/markers collected from all scopes

extra_keyword_matches = None

allow adding of extra keywords to use for matching

ihook[source]

fspath sensitive hook proxy used to call pytest hooks

warn(code, message)[source]

generate a warning with the given code and message for this item.

nodeid[source]

a ::-separated string denoting its collection tree address.

listchain()[source]

return list of all parent collectors up to self, starting from root of collection tree.

add_marker(marker)[source]

dynamically add a marker object to the node.

marker can be a string or pytest.mark.* instance.

get_marker(name)[source]

get a marker object from this node or None if the node doesn’t have a marker with that name.

listextrakeywords()[source]

Return a set of all extra keywords in self and any parents.

addfinalizer(fin)[source]

register a function to be called when this node is finalized.

This method can only be called when this node is active in a setup chain, for example during self.setup().

getparent(cls)[source]

get the next parent node (including ourself) which is an instance of the given class

class Collector[source]

Bases: _pytest.main.Node

Collector instances create children through collect() and thus iteratively build a tree.

exception CollectError[source]

Bases: exceptions.Exception

an error during collection, contains a custom message.

Collector.collect()[source]

returns a list of children (items and collectors) for this collection node.

Collector.repr_failure(excinfo)[source]

represent a collection failure.

class Item[source]

Bases: _pytest.main.Node

a basic test invocation item. Note that for a single function there might be multiple test invocation items.

class Module[source]

Bases: _pytest.main.File, _pytest.python.PyCollector

Collector for test classes and functions.

class Class[source]

Bases: _pytest.python.PyCollector

Collector for test methods.

class Function[source]

Bases: _pytest.python.FunctionMixin, _pytest.main.Item, _pytest.python.FuncargnamesCompatAttr

a Function Item is responsible for setting up and executing a Python test function.

function[source]

underlying python ‘function’ object

runtest()[source]

execute the underlying test function.

class CallInfo[source]

Result/Exception info a function invocation.

when = None

context of invocation: one of “setup”, “call”, “teardown”, “memocollect”

excinfo = None

None or ExceptionInfo object.

class TestReport[source]

Basic test report object (also used for setup and teardown calls if they fail).

nodeid = None

normalized collection node id

location = None

a (filesystempath, lineno, domaininfo) tuple indicating the actual location of a test item - it might be different from the collected one e.g. if a method is inherited from a different module.

keywords = None

a name -> value dictionary containing all keywords and markers associated with a test invocation.

outcome = None

test outcome, always one of “passed”, “failed”, “skipped”.

longrepr = None

None or a failure representation.

when = None

one of ‘setup’, ‘call’, ‘teardown’ to indicate runtest phase.

sections = None

list of (secname, data) extra information which needs to marshallable

duration = None

time it took to run just the test