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+
+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`` function argument
+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 an 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.
+
+example: setting an attribute on some class
+------------------------------------------------------
+
+If you need to patch out ``os.getcwd()`` to return an artificial
+value::
+
+    def test_some_interaction(monkeypatch):
+        monkeypatch.setattr("os.getcwd", lambda: "/")
+
+which is equivalent to the long form::
+
+    def test_some_interaction(monkeypatch):
+        import os
+        monkeypatch.setattr(os, "getcwd", lambda: "/")
+    
+
+
+Method reference of the monkeypatch function argument
+-----------------------------------------------------
+
+.. autoclass:: monkeypatch
+    :members: setattr, replace, delattr, setitem, delitem, setenv, delenv, syspath_prepend, chdir, undo
+
+``monkeypatch.setattr/delattr/delitem/delenv()`` all
+by default raise an Exception if the target does not exist.
+Pass ``raising=False`` if you want to skip this check.
+