88 lines
3.1 KiB
ReStructuredText
88 lines
3.1 KiB
ReStructuredText
|
|
Monkeypatching/mocking modules and environments
|
|
================================================================
|
|
|
|
.. currentmodule:: _pytest.monkeypatch
|
|
|
|
Sometimes tests need to invoke functionality which depends
|
|
on global settings or which invokes code which cannot be easily
|
|
tested such as network access. The ``monkeypatch`` fixture
|
|
helps you to safely set/delete an attribute, dictionary item or
|
|
environment variable or to modify ``sys.path`` for importing.
|
|
See the `monkeypatch blog post`_ for some introduction material
|
|
and a discussion of its motivation.
|
|
|
|
.. _`monkeypatch blog post`: http://tetamap.wordpress.com/2009/03/03/monkeypatching-in-unit-tests-done-right/
|
|
|
|
|
|
Simple example: monkeypatching functions
|
|
---------------------------------------------------
|
|
|
|
If you want to pretend that ``os.expanduser`` returns a certain
|
|
directory, you can use the :py:meth:`monkeypatch.setattr` method to
|
|
patch this function before calling into a function which uses it::
|
|
|
|
# content of test_module.py
|
|
import os.path
|
|
def getssh(): # pseudo application code
|
|
return os.path.join(os.path.expanduser("~admin"), '.ssh')
|
|
|
|
def test_mytest(monkeypatch):
|
|
def mockreturn(path):
|
|
return '/abc'
|
|
monkeypatch.setattr(os.path, 'expanduser', mockreturn)
|
|
x = getssh()
|
|
assert x == '/abc/.ssh'
|
|
|
|
Here our test function monkeypatches ``os.path.expanduser`` and
|
|
then calls into a function that calls it. After the test function
|
|
finishes the ``os.path.expanduser`` modification will be undone.
|
|
|
|
example: preventing "requests" from remote operations
|
|
------------------------------------------------------
|
|
|
|
If you want to prevent the "requests" library from performing http
|
|
requests in all your tests, you can do::
|
|
|
|
# content of conftest.py
|
|
import pytest
|
|
@pytest.fixture(autouse=True)
|
|
def no_requests(monkeypatch):
|
|
monkeypatch.delattr("requests.sessions.Session.request")
|
|
|
|
This autouse fixture will be executed for each test function and it
|
|
will delete the method ``request.session.Session.request``
|
|
so that any attempts within tests to create http requests will fail.
|
|
|
|
|
|
.. note::
|
|
|
|
Be advised that it is not recommended to patch builtin functions such as ``open``,
|
|
``compile``, etc., because it might break pytest's internals. If that's
|
|
unavoidable, passing ``--tb=native``, ``--assert=plain`` and ``--capture=no`` might
|
|
help although there's no guarantee.
|
|
|
|
.. note::
|
|
|
|
Mind that patching ``stdlib`` functions and some third-party libraries used by pytest
|
|
might break pytest itself, therefore in those cases it is recommended to use
|
|
:meth:`MonkeyPatch.context` to limit the patching to the block you want tested:
|
|
|
|
.. code-block:: python
|
|
|
|
import functools
|
|
def test_partial(monkeypatch):
|
|
with monkeypatch.context() as m:
|
|
m.setattr(functools, "partial", 3)
|
|
assert functools.partial == 3
|
|
|
|
See issue `#3290 <https://github.com/pytest-dev/pytest/issues/3290>`_ for details.
|
|
|
|
|
|
.. currentmodule:: _pytest.monkeypatch
|
|
|
|
API Reference
|
|
-------------
|
|
|
|
Consult the docs for the :class:`MonkeyPatch` class.
|