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:
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_sub.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 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:
To see a complete list of all plugins with their latest testing status against different py.test and Python versions, please visit plugincompat.
You may also discover more plugins through a pytest- pypi.python.org search.
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.
You can also contribute your plugin to pytest-dev once it has some happy users other than yourself.
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. pytest looks up the pytest11 entrypoint to discover its plugins and you can thus make your plugin available by defining it in your setuptools-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.
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:
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
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.
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.
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.
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.
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 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.
implements the loading of initial conftest files ahead of command line option parsing.
(deprecated) modify command line arguments before option parsing.
return initialized config object, parsing the specified args.
return dict of name->object to be made globally available in the pytest namespace. This hook is called before command line options are parsed.
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.
called for performing the main command line action. The default implementation will invoke the configure hooks and runtest_mainloop.
All runtest related hooks receive a pytest.Item object.
implements the runtest_setup/call/teardown protocol for the given test item, including capturing exceptions and calling reporting hooks.
Parameters: |
|
---|---|
Return boolean: | True if no further hook implementations should be invoked. |
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. |
---|
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.
pytest calls the following hooks for collecting files and directories:
return True to prevent considering this path for collection. This hook is consulted for all files and directories prior to calling more specific hooks.
called before traversing a directory for collection files.
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:
return custom item/collector for a python object in a module, or None.
After collection is complete, you can modify the order of items, delete or otherwise amend the test items:
Session related reporting hooks:
And here is the central hook for reporting about test execution:
There are few hooks which can be used for special reporting or interaction with exceptions:
Plugins and conftest.py files may declare new hooks that can then be implemented by other plugins in order to alter behaviour or interact with the new plugin:
called at plugin load time to allow adding new hooks via a call to pluginmanager.registerhooks(module).
Hooks are usually declared as do-nothing functions that contain only documentation describing when the hook will be called and what return values are expected.
For an example, see newhooks.py from xdist: pytest distributed testing plugin.
Using new hooks from plugins as explained above might be a little tricky because the standard Hook specification and validation mechanism: if you depend on a plugin that is not installed, validation will fail and the error message will not make much sense to your users.
One approach is to defer the hook implementation to a new plugin instead of declaring the hook functions directly in your plugin module, for example:
# contents of myplugin.py
class DeferPlugin(object):
"""Simple plugin to defer pytest-xdist hook functions."""
def pytest_testnodedown(self, node, error):
"""standard xdist hook function.
"""
def pytest_configure(config):
if config.pluginmanager.hasplugin('xdist'):
config.pluginmanager.register(DeferPlugin())
This has the added benefit of allowing you to conditionally install hooks depending on which plugins are installed.
New in version 2.7: (experimental)
pytest plugins can implement hook wrappers which which wrap the execution of other hook implementations. A hook wrapper is a generator function which yields exactly once. When pytest invokes hooks it first executes hook wrappers and passes the same arguments as to the regular hooks.
At the yield point of the hook wrapper pytest will execute the next hook implementations and return their result to the yield point in the form of a CallOutcome instance which encapsulates a result or exception info. The yield point itself will thus typically not raise exceptions (unless there are bugs).
Here is an example definition of a hook wrapper:
import pytest
@pytest.mark.hookwrapper
def pytest_pyfunc_call(pyfuncitem):
# do whatever you want before the next hook executes
outcome = yield
# outcome.excinfo may be None or a (cls, val, tb) tuple
res = outcome.get_result() # will raise if outcome was exception
# postprocess result
Note that hook wrappers don’t return results themselves, they merely perform tracing or other side effects around the actual hook implementations. If the result of the underlying hook is a mutable object, they may modify that result, however.
access to configuration values, pluginmanager and plugin hooks.
access to command line option as attributes. (deprecated), use getoption() instead
a pluginmanager instance
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.
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.
return command line option value.
Parameters: |
|
---|
Parser for command line arguments and ini-file values.
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.
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", ...).
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).
base class for Collector and Item the test collection tree. Collector subclasses have children, Items are terminal nodes.
a unique name within the scope of the parent node
the parent collector node.
the pytest config object
the session this node is part of
filesystem path where this node was collected from (can be None)
keywords/markers collected from all scopes
allow adding of extra keywords to use for matching
return list of all parent collectors up to self, starting from root of collection tree.
dynamically add a marker object to the node.
marker can be a string or pytest.mark.* instance.
get a marker object from this node or None if the node doesn’t have a marker with that name.
Bases: _pytest.main.Node
Collector instances create children through collect() and thus iteratively build a tree.
Bases: exceptions.Exception
an error during collection, contains a custom message.
Bases: _pytest.main.Node
a basic test invocation item. Note that for a single function there might be multiple test invocation items.
Bases: _pytest.main.File, _pytest.python.PyCollector
Collector for test classes and functions.
Bases: _pytest.python.FunctionMixin, _pytest.main.Item, _pytest.python.FuncargnamesCompatAttr
a Function Item is responsible for setting up and executing a Python test function.
Result/Exception info a function invocation.
context of invocation: one of “setup”, “call”, “teardown”, “memocollect”
None or ExceptionInfo object.
Basic test report object (also used for setup and teardown calls if they fail).
normalized collection node id
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.
a name -> value dictionary containing all keywords and markers associated with a test invocation.
test outcome, always one of “passed”, “failed”, “skipped”.
None or a failure representation.
one of ‘setup’, ‘call’, ‘teardown’ to indicate runtest phase.
list of (secname, data) extra information which needs to marshallable
time it took to run just the test