57 lines
2.1 KiB
Plaintext
57 lines
2.1 KiB
Plaintext
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Monkeypatching/mocking modules and environments
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================================================================
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.. currentmodule:: _pytest.monkeypatch
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Sometimes tests need to invoke functionality which depends
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on global settings or which invokes code which cannot be easily
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tested such as network access. The ``monkeypatch`` function argument
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helps you to safely set/delete an attribute, dictionary item or
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environment variable or to modify ``sys.path`` for importing.
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See the `monkeypatch blog post`_ for some introduction material
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and a discussion of its motivation.
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.. _`monkeypatch blog post`: http://tetamap.wordpress.com/2009/03/03/monkeypatching-in-unit-tests-done-right/
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Simple example: patching ``os.path.expanduser``
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---------------------------------------------------
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If, for instance, you want to pretend that ``os.expanduser`` returns a certain
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directory, you can use the :py:meth:`monkeypatch.setattr` method to
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patch this function before calling into a function which uses it::
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import os.path
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def getssh(): # pseudo application code
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return os.path.join(os.path.expanduser("~admin"), '.ssh')
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def test_mytest(monkeypatch):
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def mockreturn(path):
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return '/abc'
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monkeypatch.setattr(os.path, 'expanduser', mockreturn)
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x = getssh()
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assert x == '/abc/.ssh'
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After the test function finishes the ``os.path.expanduser`` modification
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will be undone.
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.. background check:
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$ py.test
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=========================== test session starts ============================
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platform darwin -- Python 2.7.1 -- pytest-2.1.3
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collecting ... collected 0 items
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============================= in 0.00 seconds =============================
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Method reference of the monkeypatch function argument
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-----------------------------------------------------
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.. autoclass:: monkeypatch
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:members: setattr, delattr, setitem, delitem, setenv, delenv, syspath_prepend, undo
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``monkeypatch.setattr/delattr/delitem/delenv()`` all
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by default raise an Exception if the target does not exist.
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Pass ``raising=False`` if you want to skip this check.
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