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Argument matchers for unittest.mock
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Argument matchers for unittest.mock

Version Development Status Python versions License Build Status

More robust tests

Python's mocking library (or its backport for Python <3.3) is simple, reliable, and easy to use. But it is also a little lacking when it comes to asserting what calls a mock has received.

You can be either very specific:

my_mock.assert_called_once_with(42, some_foo_object, 'certain string')

or extremely general:

my_mock.assert_called_with(ANY, ANY, ANY)
# passes as long as argument count is the same
The former can make your tests over-specified, and thus fragile.
The latter could make them too broad, missing some erroneous cases and possibly letting your code fail in production.

callee provides argument matchers that allow you to be exactly as precise as you want:

my_mock.assert_called_with(GreaterThan(0), InstanceOf(Foo), String())

without tedious, handcrafted, and poorly readable code that checks call_args or call_args_list:

self.assertGreater(mock.call_args[0][0], 0)
self.assertIsInstance(mock.call_args[0][1], Foo)
self.assertIsInstance(mock.call_args[0][2], str)

It has plenty of matcher types to fit all common and uncommon needs, and you can easily write your own if necessary.


Installing callee is easy with pip:

$ pip install callee
callee support goes all the way back to Python 2.6.
It also works both with the unittest.mock module from Python 3.3+ or its backport.

API reference

See the documentation for complete reference on the library usage and all available matchers.


Contributions are welcome! If you need ideas, head to the issue tracker or search for the various TODOs scattered around the codebase. Or just think what matchers you'd like to add :)

After cloning the repository, this should get you up and running:

# ... create virtualenv as necessary ...
pip install -r requirements-dev.txt

To regenerate documentation and display it in the browser, simply run:

inv docs

Happy hacking!

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