Mock v0.7.2 documentation

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Mock Library Comparison

A side-by-side comparison of how to accomplish some basic tasks with mock and some other popular Python mocking libraries and frameworks.

These are:

Popular python mocking frameworks not yet represented here include MiniMock.

pMock (last release 2004 and doesn’t import in recent versions of Python) and python-mock (last release 2005) are intentionally omitted.

Note

A more up to date, and tested for all mock libraries (only the mock examples on this page can be executed as doctests) version of this comparison is maintained by Gary Bernhardt:

This comparison is by no means complete, and also may not be fully idiomatic for all the libraries represented. Please contribute corrections, missing comparisons, or comparisons for additional libraries to the mock issue tracker.

This comparison page was originally created by the Mox project and then extended for flexmock and mock by Herman Sheremetyev. Dingus examples written by Gary Bernhadt. fudge examples provided by Kumar McMillan.

Note

The examples tasks here were originally created by Mox which is a mocking framework rather than a library like mock. The tasks shown naturally exemplify tasks that frameworks are good at and not the ones they make harder. In particular you can take a Mock or MagicMock object and use it in any way you want with no up-front configuration. The same is also true for Dingus.

The examples for mock here assume version 0.7.0.

Simple fake object

>>> # mock
>>> my_mock = mock.Mock()
>>> my_mock.some_method.return_value = "calculated value"
>>> my_mock.some_attribute = "value"
>>> assertEqual("calculated value", my_mock.some_method())
>>> assertEqual("value", my_mock.some_attribute)
# Flexmock
mock = flexmock(some_method=lambda: "calculated value", some_attribute="value")
assertEqual("calculated value", mock.some_method())
assertEqual("value", mock.some_attribute)

# Mox
mock = mox.MockAnything()
mock.some_method().AndReturn("calculated value")
mock.some_attribute = "value"
mox.Replay(mock)
assertEqual("calculated value", mock.some_method())
assertEqual("value", mock.some_attribute)

# Mocker
mock = mocker.mock()
mock.some_method()
mocker.result("calculated value")
mocker.replay()
mock.some_attribute = "value"
assertEqual("calculated value", mock.some_method())
assertEqual("value", mock.some_attribute)
>>> # Dingus
>>> my_dingus = dingus.Dingus(some_attribute="value",
...                           some_method__returns="calculated value")
>>> assertEqual("calculated value", my_dingus.some_method())
>>> assertEqual("value", my_dingus.some_attribute)
>>> # fudge
>>> my_fake = (fudge.Fake()
...            .provides('some_method')
...            .returns("calculated value")
...            .has_attr(some_attribute="value"))
...
>>> assertEqual("calculated value", my_fake.some_method())
>>> assertEqual("value", my_fake.some_attribute)

Simple mock

>>> # mock
>>> my_mock = mock.Mock()
>>> my_mock.some_method.return_value = "value"
>>> assertEqual("value", my_mock.some_method())
>>> my_mock.some_method.assert_called_once_with()
# Flexmock
mock = flexmock()
mock.should_receive("some_method").and_return("value").once
assertEqual("value", mock.some_method())

# Mox
mock = mox.MockAnything()
mock.some_method().AndReturn("value")
mox.Replay(mock)
assertEqual("value", mock.some_method())
mox.Verify(mock)

# Mocker
mock = mocker.mock()
mock.some_method()
mocker.result("value")
mocker.replay()
assertEqual("value", mock.some_method())
mocker.verify()
>>> # Dingus
>>> my_dingus = dingus.Dingus(some_method__returns="value")
>>> assertEqual("value", my_dingus.some_method())
>>> assert my_dingus.some_method.calls().once()
>>> # fudge
>>> @fudge.test
... def test():
...     my_fake = (fudge.Fake()
...                .expects('some_method')
...                .returns("value")
...                .times_called(1))
...
>>> test()
Traceback (most recent call last):
...
AssertionError: fake:my_fake.some_method() was not called

Creating partial mocks

>>> # mock
>>> SomeObject.some_method = mock.Mock(return_value='value')
>>> assertEqual("value", SomeObject.some_method())
# Flexmock
flexmock(SomeObject).should_receive("some_method").and_return('value')
assertEqual("value", mock.some_method())

# Mox
mock = mox.MockObject(SomeObject)
mock.some_method().AndReturn("value")
mox.Replay(mock)
assertEqual("value", mock.some_method())
mox.Verify(mock)

# Mocker
mock = mocker.mock(SomeObject)
mock.Get()
mocker.result("value")
mocker.replay()
assertEqual("value", mock.some_method())
mocker.verify()
>>> # Dingus
>>> object = SomeObject
>>> object.some_method = dingus.Dingus(return_value="value")
>>> assertEqual("value", object.some_method())
>>> # fudge
>>> fake = fudge.Fake().is_callable().returns("<fudge-value>")
>>> with fudge.patched_context(SomeObject, 'some_method', fake):
...     s = SomeObject()
...     assertEqual("<fudge-value>", s.some_method())
...

Ensure calls are made in specific order

>>> # mock
>>> my_mock = mock.Mock(spec=SomeObject)
>>> my_mock.method1()
<mock.Mock object at 0x...>
>>> my_mock.method2()
<mock.Mock object at 0x...>
>>> assertEqual(my_mock.method_calls, [('method1',), ('method2',)])
# Flexmock
mock = flexmock(SomeObject)
mock.should_receive('method1').once.ordered.and_return('first thing')
mock.should_receive('method2').once.ordered.and_return('second thing')

# Mox
mock = mox.MockObject(SomeObject)
mock.method1().AndReturn('first thing')
mock.method2().AndReturn('second thing')
mox.Replay(mock)
mox.Verify(mock)

# Mocker
mock = mocker.mock()
with mocker.order():
    mock.method1()
    mocker.result('first thing')
    mock.method2()
    mocker.result('second thing')
    mocker.replay()
    mocker.verify()
>>> # Dingus
>>> my_dingus = dingus.Dingus()
>>> my_dingus.method1()
<Dingus ...>
>>> my_dingus.method2()
<Dingus ...>
>>> assertEqual(['method1', 'method2'], [call.name for call in my_dingus.calls])
>>> # fudge
>>> @fudge.test
... def test():
...     my_fake = (fudge.Fake()
...                .remember_order()
...                .expects('method1')
...                .expects('method2'))
...     my_fake.method2()
...     my_fake.method1()
...
>>> test()
Traceback (most recent call last):
...
AssertionError: Call #1 was fake:my_fake.method2(); Expected: #1 fake:my_fake.method1(), #2 fake:my_fake.method2(), end

Raising exceptions

>>> # mock
>>> my_mock = mock.Mock()
>>> my_mock.some_method.side_effect = SomeException("message")
>>> assertRaises(SomeException, my_mock.some_method)
# Flexmock
mock = flexmock()
mock.should_receive("some_method").and_raise(SomeException("message"))
assertRaises(SomeException, mock.some_method)

# Mox
mock = mox.MockAnything()
mock.some_method().AndRaise(SomeException("message"))
mox.Replay(mock)
assertRaises(SomeException, mock.some_method)
mox.Verify(mock)

# Mocker
mock = mocker.mock()
mock.some_method()
mocker.throw(SomeException("message"))
mocker.replay()
assertRaises(SomeException, mock.some_method)
mocker.verify()
>>> # Dingus
>>> my_dingus = dingus.Dingus()
>>> my_dingus.some_method = dingus.exception_raiser(SomeException)
>>> assertRaises(SomeException, my_dingus.some_method)
>>> # fudge
>>> my_fake = (fudge.Fake()
...            .is_callable()
...            .raises(SomeException("message")))
...
>>> my_fake()
Traceback (most recent call last):
...
SomeException: message

Override new instances of a class

>>> # mock
>>> with mock.patch('somemodule.Someclass') as MockClass:
...     MockClass.return_value = some_other_object
...     assertEqual(some_other_object, somemodule.Someclass())
...
# Flexmock
flexmock(some_module.SomeClass, new_instances=some_other_object)
assertEqual(some_other_object, some_module.SomeClass())

# Mox
# (you will probably have mox.Mox() available as self.mox in a real test)
mox.Mox().StubOutWithMock(some_module, 'SomeClass', use_mock_anything=True)
some_module.SomeClass().AndReturn(some_other_object)
mox.ReplayAll()
assertEqual(some_other_object, some_module.SomeClass())

# Mocker
# (TODO)
>>> # Dingus
>>> MockClass = dingus.Dingus(return_value=some_other_object)
>>> with dingus.patch('somemodule.SomeClass', MockClass):
...     assertEqual(some_other_object, somemodule.SomeClass())
...
>>> # fudge
>>> @fudge.patch('somemodule.SomeClass')
... def test(FakeClass):
...     FakeClass.is_callable().returns(some_other_object)
...     assertEqual(some_other_object, somemodule.SomeClass())
...
>>> test()

Call the same method multiple times

Note

You don’t need to do any configuration to call mock.Mock() methods multiple times. Attributes like call_count, call_args_list and method_calls provide various different ways of making assertions about how the mock was used.

>>> # mock
>>> my_mock = mock.Mock()
>>> my_mock.some_method()
<mock.Mock object at 0x...>
>>> my_mock.some_method()
<mock.Mock object at 0x...>
>>> assert my_mock.some_method.call_count >= 2
# Flexmock # (verifies that the method gets called at least twice)
flexmock(some_object).should_receive('some_method').at_least.twice

# Mox
# (does not support variable number of calls, so you need to create a new entry for each explicit call)
mock = mox.MockObject(some_object)
mock.some_method(mox.IgnoreArg(), mox.IgnoreArg())
mock.some_method(mox.IgnoreArg(), mox.IgnoreArg())
mox.Replay(mock)
mox.Verify(mock)

# Mocker
# (TODO)
>>> # Dingus
>>> my_dingus = dingus.Dingus()
>>> my_dingus.some_method()
<Dingus ...>
>>> my_dingus.some_method()
<Dingus ...>
>>> assert len(my_dingus.calls('some_method')) == 2
>>> # fudge
>>> @fudge.test
... def test():
...     my_fake = fudge.Fake().expects('some_method').times_called(2)
...     my_fake.some_method()
...
>>> test()
Traceback (most recent call last):
...
AssertionError: fake:my_fake.some_method() was called 1 time(s). Expected 2.

Mock chained methods

>>> # mock
>>> my_mock = mock.Mock()
>>> method3 = my_mock.method1.return_value.method2.return_value.method3
>>> method3.return_value = 'some value'
>>> assertEqual('some value', my_mock.method1().method2().method3(1, 2))
>>> method3.assert_called_once_with(1, 2)
# Flexmock
# (intermediate method calls are automatically assigned to temporary fake objects
# and can be called with any arguments)
flexmock(some_object).should_receive(
    'method1.method2.method3'
).with_args(arg1, arg2).and_return('some value')
assertEqual('some_value', some_object.method1().method2().method3(arg1, arg2))
# Mox
mock = mox.MockObject(some_object)
mock2 = mox.MockAnything()
mock3 = mox.MockAnything()
mock.method1().AndReturn(mock1)
mock2.method2().AndReturn(mock2)
mock3.method3(arg1, arg2).AndReturn('some_value')
self.mox.ReplayAll()
assertEqual("some_value", some_object.method1().method2().method3(arg1, arg2))
self.mox.VerifyAll()

# Mocker
# (TODO)
>>> # Dingus
>>> my_dingus = dingus.Dingus()
>>> method3 = my_dingus.method1.return_value.method2.return_value.method3
>>> method3.return_value = 'some value'
>>> assertEqual('some value', my_dingus.method1().method2().method3(1, 2))
>>> assert method3.calls('()', 1, 2).once()
>>> # fudge
>>> @fudge.test
... def test():
...     my_fake = fudge.Fake()
...     (my_fake
...      .expects('method1')
...      .returns_fake()
...      .expects('method2')
...      .returns_fake()
...      .expects('method3')
...      .with_args(1, 2)
...      .returns('some value'))
...     assertEqual('some value', my_fake.method1().method2().method3(1, 2))
...
>>> test()

Mocking a context manager

Examples for mock, Dingus and fudge only (so far):

>>> # mock
>>> my_mock = mock.MagicMock()
>>> with my_mock:
...     pass
...
>>> my_mock.__enter__.assert_called_with()
>>> my_mock.__exit__.assert_called_with(None, None, None)
>>> # Dingus (nothing special here; all dinguses are "magic mocks")
>>> my_dingus = dingus.Dingus()
>>> with my_dingus:
...     pass
...
>>> assert my_dingus.__enter__.calls()
>>> assert my_dingus.__exit__.calls('()', None, None, None)
>>> # fudge
>>> my_fake = fudge.Fake().provides('__enter__').provides('__exit__')
>>> with my_fake:
...     pass
...

Mocking the builtin open used as a context manager

Example for mock only (so far):

>>> # mock
>>> my_mock = mock.MagicMock()
>>> with mock.patch('__builtin__.open', my_mock):
...     manager = my_mock.return_value.__enter__.return_value
...     manager.read.return_value = 'some data'
...     with open('foo') as h:
...         data = h.read()
...
>>> data
'some data'
>>> my_mock.assert_called_once_with('foo')

or:

>>> # mock
>>> with mock.patch('__builtin__.open') as my_mock:
...     my_mock.return_value.__enter__ = lambda s: s
...     my_mock.return_value.__exit__ = mock.Mock()
...     my_mock.return_value.read.return_value = 'some data'
...     with open('foo') as h:
...         data = h.read()
...
>>> data
'some data'
>>> my_mock.assert_called_once_with('foo')
>>> # Dingus
>>> my_dingus = dingus.Dingus()
>>> with dingus.patch('__builtin__.open', my_dingus):
...     file_ = open.return_value.__enter__.return_value
...     file_.read.return_value = 'some data'
...     with open('foo') as h:
...         data = f.read()
...
>>> data
'some data'
>>> assert my_dingus.calls('()', 'foo').once()
>>> # fudge
>>> from contextlib import contextmanager
>>> from StringIO import StringIO
>>> @contextmanager
... def fake_file(filename):
...     yield StringIO('sekrets')
...
>>> with fudge.patch('__builtin__.open') as fake_open:
...     fake_open.is_callable().calls(fake_file)
...     with open('/etc/password') as f:
...         data = f.read()
...
fake:__builtin__.open
>>> data
'sekrets'