Python Mock Autospec vs Spec

Question

Trying to wrap my head around the difference between Spec and Autospec. They seem to be about the same. Specifically, if you look at mock.patch decorator.

Can someone explain when to use which?

https://docs.python.org/3/library/unittest.mock.html

Answer 1

spec applies only to the mock instance where it is specified. In particular, if the mocked class a has a method, e.g. method(), then calling that method in the instanciated mock of a will automatically generate and return another mock that is not restricted to any spec. This is where autospec comes in handy, as it recursively defines specs on whatever is called (within the restrictions of the specs defined up to that point).

From the Mock Autospeccing Helper documentation:

If you use a class or instance as the spec for a mock then you can only access attributes on the mock that exist on the real class:

>>> import urllib2
>>> mock = Mock(spec=urllib2.Request)
>>> mock.assret_called_with
Traceback (most recent call last):
...
AttributeError: Mock object has no attribute 'assret_called_with'

The spec only applies to the mock itself, so we still have the same issue with any methods on the mock:

>>> mock.has_data()
<mock.Mock object at 0x...>
>>> mock.has_data.assret_called_with()

Auto-speccing solves this problem.