Mock#

Links#

unittest.mock Python doc

Asserts#

Assert Methods#

assert_called()
assert_called_once()
assert_called_with(*args, **kwargs) - only passes if the call is the most recent one
assert_called_once_with(*args, **kwargs) - passes if the mock was called exactly once with the specified arguments
assert_any_call(*args, **kwargs) - passes if the mock has ever been called with the specified arguments
assert_has_calls(calls, any_order=False)
assert_not_called()

Assert only some Arguments#

Assert not all exact arguments but just some of them.

Example:

from unittest.mock import Mock, ANY
mock = Mock(return_value=None)
mock("foo", bar="something_I_do_not_care_about")
mock.assert_called_once_with("foo", bar=ANY)

Spy#

If you do not want to replace a function with a mock, but want to observe the parameters passed to the function, a so-called spy can be used.

Spy on a Function#

To do this we use a combination of patch and the wraps argument. Note that the first argument of patch is a string.

Example:

def my_function(x):
    return x + 1

with patch("__main__.my_function", wraps=my_function) as wrapped_function:
    result = my_function(5)
    assert result == 6
    wrapped_function.assert_called_once_with(5)

Spy on a Method#

To do this we use a combination of patch.object and the wraps argument. Note that the first argument of patch.object is a object (instance).

Example:

class MyClass:
    def my_function(self, x):
        return x + 1

my_instance = MyClass()
with patch.object(my_instance, 'my_function', wraps=my_instance.my_function) as wrapped_method:
    result = my_instance.my_function(5)
    assert result == 6
    wrapped_method.assert_called_once_with(5)

Seal a Mock#

Seal disables the automatic creation of mocks when accessing an attribute of the mock. Also see: https://docs.python.org/3/library/unittest.mock.html#unittest.mock.seal

One problem with normal mocks is that they auto-create attributes on demand. If you misspell one of these assert methods then your assertion is simply swallowed and ignored. If you seal the mock after creation this avoids this problem.

Example:

from unittest.mock import Mock, seal
mock = Mock()
# more configuration here
seal(mock)