Mocking of Selector

Mock of selectors and compatible objects performing asynchronous IO.

This module provides classes to mock objects performing IO (files, sockets, etc). These mocks are compatible with TestSelector, which can simulate the behavior of a selector on the mock objects, or forward actual work to a real selector.

Mocking file-like objects

class asynctest.FileMock(*args, parent=None, **kwargs)[source]

Mock a file-like object.

A FileMock is an intelligent mock which can work with TestSelector to simulate IO events during tests.


Return a FileDescriptor object.

class asynctest.SocketMock(side_effect=None, return_value=sentinel.DEFAULT, wraps=None, name=None, spec_set=None, parent=None, **kwargs)[source]

Bases: asynctest.selector.FileMock

Mock a socket.

See FileMock.

class asynctest.SSLSocketMock(side_effect=None, return_value=sentinel.DEFAULT, wraps=None, name=None, spec_set=None, parent=None, **kwargs)[source]

Bases: asynctest.selector.SocketMock

Mock a socket wrapped by the ssl module.

See FileMock.

New in version 0.5.

class asynctest.FileDescriptor[source]

Bases: int

A subclass of int which allows to identify the virtual file-descriptor of a FileMock.

If FileDescriptor() without argument, its value will be the value of next_fd.

When an object is created, next_fd is set to the highest value for a FileDescriptor object + 1.

next_fd = 0



Return the FileDescriptor value of fileobj.

If fileobj is a FileDescriptor, fileobj is returned, else fileobj.fileno() is returned instead.

Note that if fileobj is an int, ValueError is raised.

Raises:ValueError – if filobj is not a FileMock, a file-like object or a FileDescriptor.

Return True if the obj or obj.fileno() is a asynctest.FileDescriptor.

Mocking the selector

class asynctest.TestSelector(selector=None)[source]

A selector which supports IOMock objects.

It can wrap an actual implementation of a selector, so the selector will work both with mocks and real file-like objects.

A common use case is to patch the selector loop:

loop._selector = asynctest.TestSelector(loop._selector)
Parameters:selector – optional, if provided, this selector will be used to work with real file-like objects.

Close the selector.

Close the actual selector if supplied, unregister all mocks.

See selectors.BaseSelector.close().

modify(fileobj, events, data=None)[source]

Shortcut when calling TestSelector.unregister() then TestSelector.register() to update the registration of a an object to the selector.

See selectors.BaseSelector.modify().

register(fileobj, events, data=None)[source]

Register a file object or a FileMock.

If a real selector object has been supplied to the TestSelector object and fileobj is not a FileMock or a FileDescriptor returned by FileMock.fileno(), the object will be registered to the real selector.

See selectors.BaseSelector.register().


Perfom the selection.

This method is a no-op if no actual selector has been supplied.



Unregister a file object or a FileMock.

See selectors.BaseSelector.unregister().


asynctest.set_read_ready(fileobj, loop)[source]

Schedule callbacks registered on loop as if the selector notified that data is ready to be read on fileobj.

mock = asynctest.SocketMock()
mock.recv.return_value = b"Data"

def read_ready(sock):
    print("received:", sock.recv(1024))

loop.add_reader(mock, read_ready, mock)


loop.run_forever() # prints received: b"Data"

New in version 0.4.

asynctest.set_write_ready(fileobj, loop)[source]

Schedule callbacks registered on loop as if the selector notified that data can be written to fileobj.


New in version 0.4.