Mock

Created for the Django Toronto meetup, a quick tour through the Python mock package.

Transcript

1. mock==0.8.0
   

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2. Who am I?
   Dan Langer
   @dlanger
   daniel@langer.me
   daniel.langer.me
   

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5. >> import mock
   >> dir(mock)
   ['Mock', 'patch', ...]
   

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6. >> from mock import Mock
   

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7. Mocks all the way down
   >> k = Mock()
   >> k.foo.bar
   
   >> k.foo.bar
   
   

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8. Configure your mocks
   >> from django.contrib.auth.models
   import User
   >> user1_mock = Mock()
   >> user1_mock.foo
   
   >> user2_mock = Mock(spec=User)
   >> user2_mock.foo
   AttributeError: ...
   

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9. Configure your mocks
   >> rmock = Mock(return_value=5)
   >> rmock(), rmock(4), rmock("W")
   (5, 5, 5)
   >> smock = Mock(side_effect=[1,2])
   >> smock(), smock()
   (1, 2)
   >> emock = Mock(side_effect=Exception)
   >> emock()
   Exception: ...
   

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10. Inspect your mocks
    >> imock = Mock(return_value=None)
    >> imock()
    >> imock.call_count
    1
    >> imock(1, 2, 3, demo="ok")
    >> imock.call_args_list
    [call(1), call(1,2,3,demo='ok')]
    

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11. >> from mock import patch
    

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12. Daniel Coomber
    

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13. Patch all the things
    # utils.py
    def load_token(user)
    r = StrictRedis(host=...)
    [...]
    raw_token = r.rpop(token_id)
    return '--'.join([raw_token, ...])
    # tests.py
    def test_load_token(self):
    redis_mock = Mock()
    redis_mock.return_value.rpop \
    .return_value = 'TEST_TOKEN'
    with patch('utils.StrictRedis', redis_mock):
    load_token(self.test_user)
    self.assertEqual(...)
    

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14. Patch celery
    # tasks.py
    @task
    def process_chunk(chunk):
    pass
    @task
    def process_file(file):
    tasks = []
    for ...
    st = process_chunk.subtask(chunk)
    tasks.append(st)
    process = TaskSet(tasks=tasks)
    process.apply_async()
    

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15. Patch celery
    # tests.py
    def test_process_file__two_subtasks(self):
    pc_mock = Mock()
    with patch('tasks.process_chunk',
    pc_mock):
    process_file.delay(...)
    self.assertEqual(pc_mock.call_count, 2)
    #Fails
    

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16. Patch celery
    # tests.py
    def test_process_file__two_subtasks(self):
    pc_mock = Mock()
    with patch('tasks.process_chunk.subtask',
    pc_mock):
    process_file.delay(...)
    self.assertEqual(pc_mock.call_count, 2)
    

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17. Patch built-ins
    # utils.py
    import message_defs
    def load_defaults(id)
    if getattr(message_defs, id, None):
    [...]
    # tests.py
    def test_load_defaults(self):
    with patch('__builtins__.getattr',
    return_value='Hi'):
    load_defaults('welcome')
    self.assertEqual(...)
    

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18. Patch built-ins
    # utils.py
    import message_defs
    def load_defaults(id)
    if getattr(message_defs, id, None):
    [...]
    # tests.py
    def test_load_defaults(self):
    with patch('utils.getattr',
    create=True,
    return_value='Hi'):
    load_defaults('welcome')
    self.assertEqual(...)
    

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19. Patch Django
    def test_template:
    mock_get_template = Mock(
    return_value=Template("Hi {{ username }}"))
    with patch('package.module.get_template',
    mock_get_template):
    [...]
    def test_verify_user(self):
    mock_get = Mock()
    mock_get.return_value = Mock(spec=User)
    with patch('utils.User.objects.get',
    mock_get):
    [...]
    

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20. Patch the ORM...sparingly
    # User.objects.filter(...).exclude(...) \
    # .order_by(...)
    def test_user_filter(self):
    mock_filter = Mock()
    mock_filter.return_value.exclude \
    .return_value.order_by.return_value = [...]
    with patch('utils.User.objects.filter',
    mock_filter):
    [...]
    

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21. Keep Reading
    @decorator syntax
    create_autospec
    MagicMock [...]
    http://www.voidspace.org.
    uk/python/mock/
    

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