Creating mocks

Decoy mocks are flexible objects that can be used in place of a class instance or a callable object, like a function. Mocks are created using the decoy.Decoy.mock method.

Default behaviors

Decoy mock objects are flexible, callable proxy objects that simply record interactions made with the object. Accessing any property of the mock will return a child mock, and calling the mock itself or any "method" of the mock will return None.

my_mock = decoy.mock(name="my_mock")

assert my_mock() is None
assert my_mock.some_method("hello world") is None
assert my_mock.some_property.some_method("hey") is None

You can configure a mock's behaviors using decoy.when. You can make assertions about how a mock was called using decoy.verify.

Mocking a class

To mock a class instance, pass the cls argument to decoy.mock. Decoy will inspect type annotations and method signatures to set a name for use in assertion messages, configure methods as synchronous or asynchronous, and understand function keyword arguments.

some_dependency = decoy.mock(cls=SomeDependency)

To type checkers, the mock will appear to have the exact same type as the cls argument. The mock will also pass isinstance checks.

Mocking a function

To mock a function, pass the func argument to decoy.mock. Decoy will inspect func to set a name for use in assertion messages, configure the mock as synchronous or asynchronous, and understand function keyword arguments.

mock_function = decoy.mock(func=some_function)

To type checkers, the mock will appear to have the exact same type as the func argument. The function mock will pass inspect.signature checks.

Creating a mock without a spec

You can call decoy.mock without using cls or func. A spec-less mock is useful for dependency interfaces like callback functions.

When creating a mock without a spec, you must use the name argument to give the mock a name to use in assertion messages. You must use the is_async argument if the created mock will be used as an asynchronous callable.

callback = decoy.mock(name="callback")
async_callback = decoy.mock(name="async_callback", is_async=True)