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_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 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 pytest-plugs.
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.
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.
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 mechanisms, capsys and capfd function arguments. |
_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 py.test |
_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 py.test and py.test 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.
return initialized config object, parsing the specified args.
return dict of name->object to be made globally available in the py.test/pytest namespace. This hook is called before command line options are parsed.
add optparse-style options and ini-style config values via calls to parser.addoption and parser.addini(...).
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: | nexitem – 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:
access to configuration values, pluginmanager and plugin hooks.
command line option values, usually added via parser.addoption(...) or parser.getgroup(...).addoption(...) calls
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 parse.addini call (usually from a plugin), a ValueError is raised.
Parser for command line arguments.
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)
fspath sensitive hook proxy used to call pytest hooks
keywords/markers collected from all scopes
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