Pytest API and builtin fixtures

This is a list of pytest.* API functions and fixtures.

For information on plugin hooks and objects, see Writing plugins.

For information on the pytest.mark mechanism, see Marking test functions with attributes.

For the below objects, you can also interactively ask for help, e.g. by typing on the Python interactive prompt something like:

import pytest
help(pytest)

Invoking pytest interactively

main(args=None, plugins=None)[source]

return exit code, after performing an in-process test run.

Parameters:
  • args – list of command line arguments.
  • plugins – list of plugin objects to be auto-registered during initialization.

More examples at Calling pytest from Python code

Helpers for assertions about Exceptions/Warnings

raises(expected_exception, *args, **kwargs)[source]

assert that a code block/function call raises expected_exception and raise a failure exception otherwise.

This helper produces a ExceptionInfo() object (see below).

If using Python 2.5 or above, you may use this function as a context manager:

>>> with raises(ZeroDivisionError):
...    1/0

Note

When using pytest.raises as a context manager, it’s worthwhile to note that normal context manager rules apply and that the exception raised must be the final line in the scope of the context manager. Lines of code after that, within the scope of the context manager will not be executed. For example:

>>> with raises(OSError) as exc_info:
        assert 1 == 1  # this will execute as expected
        raise OSError(errno.EEXISTS, 'directory exists')
        assert exc_info.value.errno == errno.EEXISTS  # this will not execute

Instead, the following approach must be taken (note the difference in scope):

>>> with raises(OSError) as exc_info:
        assert 1 == 1  # this will execute as expected
        raise OSError(errno.EEXISTS, 'directory exists')

    assert exc_info.value.errno == errno.EEXISTS  # this will now execute

Or you can specify a callable by passing a to-be-called lambda:

>>> raises(ZeroDivisionError, lambda: 1/0)
<ExceptionInfo ...>

or you can specify an arbitrary callable with arguments:

>>> def f(x): return 1/x
...
>>> raises(ZeroDivisionError, f, 0)
<ExceptionInfo ...>
>>> raises(ZeroDivisionError, f, x=0)
<ExceptionInfo ...>

A third possibility is to use a string to be executed:

>>> raises(ZeroDivisionError, "f(0)")
<ExceptionInfo ...>
class ExceptionInfo(tup=None, exprinfo=None)[source]

wraps sys.exc_info() objects and offers help for navigating the traceback.

type = None

the exception class

value = None

the exception instance

tb = None

the exception raw traceback

typename = None

the exception type name

traceback = None

the exception traceback (_pytest._code.Traceback instance)

exconly(tryshort=False)[source]

return the exception as a string

when ‘tryshort’ resolves to True, and the exception is a _pytest._code._AssertionError, only the actual exception part of the exception representation is returned (so ‘AssertionError: ‘ is removed from the beginning)

errisinstance(exc)[source]

return True if the exception is an instance of exc

getrepr(showlocals=False, style='long', abspath=False, tbfilter=True, funcargs=False)[source]

return str()able representation of this exception info. showlocals: show locals per traceback entry style: long|short|no|native traceback style tbfilter: hide entries (where __tracebackhide__ is true)

in case of style==native, tbfilter and showlocals is ignored.

Note

Similar to caught exception objects in Python, explicitly clearing local references to returned ExceptionInfo objects can help the Python interpreter speed up its garbage collection.

Clearing those references breaks a reference cycle (ExceptionInfo –> caught exception –> frame stack raising the exception –> current frame stack –> local variables –> ExceptionInfo) which makes Python keep all objects referenced from that cycle (including all local variables in the current frame) alive until the next cyclic garbage collection run. See the official Python try statement documentation for more detailed information.

Examples at Assertions about expected exceptions.

deprecated_call(func=None, *args, **kwargs)[source]

assert that calling func(*args, **kwargs) triggers a DeprecationWarning or PendingDeprecationWarning.

This function can be used as a context manager:

>>> with deprecated_call():
...    myobject.deprecated_method()

Note: we cannot use WarningsRecorder here because it is still subject to the mechanism that prevents warnings of the same type from being triggered twice for the same module. See #1190.

Comparing floating point numbers

Raising a specific test outcome

You can use the following functions in your test, fixture or setup functions to force a certain test outcome. Note that most often you can rather use declarative marks, see Skip and xfail: dealing with tests that can not succeed.

fail(msg='', pytrace=True)[source]

explicitly fail an currently-executing test with the given Message.

Parameters:pytrace – if false the msg represents the full failure information and no python traceback will be reported.
skip(msg='')[source]

skip an executing test with the given message. Note: it’s usually better to use the pytest.mark.skipif marker to declare a test to be skipped under certain conditions like mismatching platforms or dependencies. See the pytest_skipping plugin for details.

importorskip(modname, minversion=None)[source]

return imported module if it has at least “minversion” as its __version__ attribute. If no minversion is specified the a skip is only triggered if the module can not be imported.

xfail(reason='')[source]

xfail an executing test or setup functions with the given reason.

exit(msg)[source]

exit testing process as if KeyboardInterrupt was triggered.

Fixtures and requests

To mark a fixture function:

Tutorial at pytest fixtures: explicit, modular, scalable.

The request object that can be used from fixture functions.

Builtin fixtures/function arguments

You can ask for available builtin or project-custom fixtures by typing:

$ pytest -q --fixtures
cache
    Return a cache object that can persist state between testing sessions.

    cache.get(key, default)
    cache.set(key, value)

    Keys must be a ``/`` separated value, where the first part is usually the
    name of your plugin or application to avoid clashes with other cache users.

    Values can be any object handled by the json stdlib module.
capsys
    Enable capturing of writes to sys.stdout/sys.stderr and make
    captured output available via ``capsys.readouterr()`` method calls
    which return a ``(out, err)`` tuple.
capfd
    Enable capturing of writes to file descriptors 1 and 2 and make
    captured output available via ``capfd.readouterr()`` method calls
    which return a ``(out, err)`` tuple.
doctest_namespace
    Inject names into the doctest namespace.
pytestconfig
    the pytest config object with access to command line opts.
record_xml_property
    Add extra xml properties to the tag for the calling test.
    The fixture is callable with ``(name, value)``, with value being automatically
    xml-encoded.
monkeypatch
    The returned ``monkeypatch`` fixture provides these
    helper methods to modify objects, dictionaries or os.environ::

    monkeypatch.setattr(obj, name, value, raising=True)
    monkeypatch.delattr(obj, name, raising=True)
    monkeypatch.setitem(mapping, name, value)
    monkeypatch.delitem(obj, name, raising=True)
    monkeypatch.setenv(name, value, prepend=False)
    monkeypatch.delenv(name, value, raising=True)
    monkeypatch.syspath_prepend(path)
    monkeypatch.chdir(path)

    All modifications will be undone after the requesting
    test function or fixture has finished. The ``raising``
    parameter determines if a KeyError or AttributeError
    will be raised if the set/deletion operation has no target.
recwarn
    Return a WarningsRecorder instance that provides these methods:

    * ``pop(category=None)``: return last warning matching the category.
    * ``clear()``: clear list of warnings

    See http://docs.python.org/library/warnings.html for information
    on warning categories.
tmpdir_factory
    Return a TempdirFactory instance for the test session.
tmpdir
    Return a temporary directory path object
    which is unique to each test function invocation,
    created as a sub directory of the base temporary
    directory.  The returned object is a `py.path.local`_
    path object.

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