safely patch object attributes, dicts and environment variables.
Use the monkeypatch funcarg to tweak your global test environment for running a particular test. You can safely set/del an attribute, dictionary item or environment variable by respective methods on the monkeypatch funcarg. If you want e.g. to set an ENV1 variable and have os.path.expanduser return a particular directory, you can write it down like this:
def test_mytest(monkeypatch):
monkeypatch.setenv('ENV1', 'myval')
monkeypatch.setattr(os.path, 'expanduser', lambda x: '/tmp/xyz')
... # your test code that uses those patched values implicitely
After the test function finished all modifications will be undone, because the monkeypatch.undo() method is registered as a finalizer.
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.
To prepend a value to an already existing environment parameter:
def test_mypath_finding(monkeypatch):
monkeypatch.setenv('PATH', 'x/y', prepend=":")
# in bash language: export PATH=x/y:$PATH
At the end of function execution py.test invokes a teardown hook which undoes all monkeypatch changes. If you do not want to wait that long you can call finalization explicitely:
monkeypatch.undo()
This will undo previous changes. This call consumes the undo stack. Calling it a second time has no effect unless you start monkeypatching after the undo call.
The returned monkeypatch funcarg 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)
All modifications will be undone when the requesting test function finished its execution. For the del methods the raising parameter determines if a KeyError or AttributeError will be raised if the deletion has no target.
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