Create a mock

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.mock method.

Default behaviors

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.

Mock 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 and inspect.signature checks.

Mock 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-free 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)

Mock an async function or method

If you pass Decoy a cls or func with asynchronous methods or functions, Decoy will automatically create asynchronous mocks. When creating mocks without cls or func, you can use the is_async option to create an asynchronous mock manually:

async_mock = decoy.mock(name="async_mock", is_async=True)