The slides of a talk I held at the "Django User Group Meetup Berlin" on the 02-21-2012.

1. from mock import Mock
mocking for python

2. Mocking
>>> from mock import Mock
>>> Mock()
<Mock id='4419885840'>
Calling an undefined method on the mock
returns the mock.

3. Mocking
>>> m = Mock(return_value='foo')
>>> m()
'foo'
Mocks can have return values.

4. Mocking
>>> m('bar', answer=42)
'foo'
>>> m.called
True
>>> m.call_args
call('bar', answer=42)
>>> m.call_count
1
Calls to the mock can be inspected.

5. Mocking
>>> mock = Mock()
>>> mock.side_effect = Exception('Bam')
>>> mock()
Traceback (most recent call last):
...
Exception: Bam
>>> mock.side_effect = [3, 2, 1]
>>> mock(), mock(), mock()
(3, 2, 1)
Mocks can have side effects.

6. Documentation
http://www.voidspace.org.uk/python/mock/mock.html

7. Patching
>>> class Class(object):
... def method(self):
... pass
...
>>> with patch('__main__.Class') as M:
... instance = M()
... instance.method.return_value = 'foo'
... assert Class() is instance
... assert Class().method() == 'foo'
...

8. Live example

9. Patching
@patch('paperc.base.utils.mail.EmailMultiAlternatives')
def test_html_parameter_is_optional(self, EmailMultiAlternatives):
'''
Omitting the html parameter should send the email with plain
text only.
'''
msg = Mock()
EmailMultiAlternatives.return_value = msg
send_email(*['email', 'subject', 'text', {}])
self.assertEquals(msg.attach_alternative.call_count, 0)

10. mock Library Author
• Michael Foord
• http://www.voidspace.org.uk/python/mock/
index.html
• @voidspace