================
 The Mock Class
================

.. currentmodule:: mock

.. testsetup::

    import os, sys
    if not os.getcwd() in sys.path:
        sys.path.append(os.getcwd())
    from mock import Mock, sentinel, DEFAULT

``Mock`` is a flexible mock object intended to replace the use of stubs and
test doubles throughout your code. Mocks are callable and create attributes as
new mocks when you access them [#]_. Accessing the same attribute will always
return the same mock. Mocks record how you use them, allowing you to make
assertions about what your code has done to them.

The :func:`mock.patch` decorators makes it easy to temporarily replace classes
in a particular module with a Mock object.

.. index:: __init__

.. class:: Mock(spec=None, side_effect=None, return_value=DEFAULT, wraps=None)

    Create a new ``Mock`` object. ``Mock`` takes several optional arguments
    that specify the behaviour of the Mock object:

    * ``spec``: This can be either a list of strings or an existing object (a
      class or instance) that acts as the specification for the mock object. If
      you pass in an object then a list of strings is formed by calling dir on
      the object (excluding unsupported magic attributes and methods). Accessing
      any attribute not in this list will raise an ``AttributeError``.
    
    * ``side_effect``: A function to be called whenever the Mock is called. See 
      the :attr:`Mock.side_effect` attribute. Useful for raising exceptions or 
      dynamically changing return values. The function is called with the same 
      arguments as the mock, and unless it returns :data:`DEFAULT`, the return 
      value of this function is used as the return value.
      
      Alternatively ``side_effect`` can be an exception class or instance. In
      this case the exception will be raised when the mock is called.

    * ``return_value``: The value returned when the mock is called. By default
      this is a new Mock (created on first access). See the
      :attr:`Mock.return_value` attribute.
    
    * ``wraps``: Item for the mock object to wrap. If ``wraps`` is not None
      then calling the Mock will pass the call through to the wrapped object
      (returning the real result and ignoring ``return_value``). Attribute
      access on the mock will return a Mock object that wraps the corresponding
      attribute of the wrapped object (so attempting to access an attribute that
      doesn't exist will raise an ``AttributeError``).
        
      If the mock has an explicit ``return_value`` set then calls are not passed
      to the wrapped object and the ``return_value`` is returned instead.


Methods
=======

.. method:: Mock.assert_called_with(*args, **kwargs)

    This method is a convenient way of asserting that calls are made in a particular way:

    .. doctest::
    
        >>> mock = Mock()
        >>> mock.method(1, 2, 3, test='wow')
        <mock.Mock object at 0x...>
        >>> mock.method.assert_called_with(1, 2, 3, test='wow')


.. method:: Mock.reset_mock()

    The reset_mock method resets all the call attributes on a mock object:
    
    .. doctest::

        >>> mock = Mock()
        >>> mock('hello')
        <mock.Mock object at 0x...>
        >>> mock.called
        True
        >>> mock.reset_mock()
        >>> mock.called
        False

    This can be useful where you want to make a series of assertions that reuse the same object. Note that ``reset`` *doesn't* clear the return value, ``side_effect`` or any child attributes. Attributes you have set using normal assignment are also left in place. Child mocks and the return value mock (if any) are reset as well.


.. index:: __call__

Calling
=======
    
Mock objects are callable. The call will return the value set as the :attr:`Mock.return_value` attribute. The default return value is a new Mock object; it is created the first time the return value is accessed (either explicitly or by calling the Mock) - but it is stored and the same one returned each time.

Calls made to the object will be recorded in the attributes_.

If :attr:`Mock.side_effect` is set then it will be called after the call has been recorded but before any value is returned.


Attributes
==========

.. attribute:: Mock.called

    A boolean representing whether or not the mock object has been called:

    .. doctest::

        >>> mock = Mock(return_value=None)
        >>> mock.called
        False
        >>> mock()
        >>> mock.called
        True

.. attribute:: Mock.call_count

    An integer telling you how many times the mock object has been called:

    .. doctest::

        >>> mock = Mock(return_value=None)
        >>> mock.call_count
        0
        >>> mock()
        >>> mock()
        >>> mock.call_count
        2
        
        
.. attribute:: Mock.return_value

    Set this to configure the value returned by calling the mock:

    .. doctest::

        >>> mock = Mock()
        >>> mock.return_value = 'fish'
        >>> mock()
        'fish'
    
    The default return value is a mock object and you can configure it in the normal way:
    
    .. doctest::

        >>> mock = Mock()
        >>> mock.return_value.attribute = sentinel.Attribute
        >>> mock.return_value()
        <mock.Mock object at 0x...>
        >>> mock.return_value.assert_called_with()


.. attribute:: Mock.side_effect


    This can either be a function to be called when the mock is called, or an
    exception (class or instance) to raised.
    
    If you pass in a function it will be called with same arguments as the mock
    and unless the mock returns the DEFAULT singleton the mock will return
    whatever the function returns. If the function returns default then the
    mock will return its normal value (from the :attr:`Mock.return_value`.
    
    An example of a mock that raises an exception (to test exception handling of
    an API):
    
    .. doctest::

        >>> mock = Mock()
        >>> mock.side_effect = Exception('Boom!')
        >>> mock()
        Traceback (most recent call last):
          ...
        Exception: Boom!

    Using ``side_effect`` to return a sequence of values:
    
    .. doctest::

        >>> mock = Mock()
        >>> results = [1, 2, 3]
        >>> def side_effect(*args, **kwargs):
        ...     return results.pop()
        ... 
        >>> mock.side_effect = side_effect
        >>> mock(), mock(), mock()
        (3, 2, 1)

    The side_effect function is called with the same arguments as the mock (so it is wise for it to take arbitrary args and keyword arguments) and whatever it returns is used
    as the return value for the call. The exception is if it returns :data:`DEFAULT`, in which case the normal :attr:`Mock.return_value` is used.
    
    .. doctest::

        >>> mock = Mock(return_value=3)
        >>> def side_effect(*args, **kwargs):
        ...     return DEFAULT
        ... 
        >>> mock.side_effect = side_effect
        >>> mock()
        3

.. attribute:: Mock.call_args

    This is either ``None`` (if the mock hasn't been called), or the arguments that the mock was last called with. This will be in the form of a tuple: the first member is any ordered arguments the mock was called with (or an empty tuple) and the second member is any keyword arguments (or an empty dictionary):
    
    .. doctest::

        >>> mock = Mock(return_value=None)
        >>> print mock.call_args
        None
        >>> mock()
        >>> mock.call_args
        ((), {})
        >>> 
        >>> mock(3, 4, 5, key='fish', next='w00t!')
        >>> mock.call_args
        ((3, 4, 5), {'key': 'fish', 'next': 'w00t!'})


.. attribute:: Mock.call_args_list

    This is a list of all the calls made to the mock object in sequence (so the length of the list is the number of times it has been called). Before any calls have been made it is an empty list:
    
    .. doctest::

        >>> mock = Mock()
        >>> mock()
        <mock.Mock object at 0x...>
        >>> mock(3, 4, 5, key='fish', next='w00t!')
        <mock.Mock object at 0x...>
        >>> mock.call_args_list
        [((), {}), ((3, 4, 5), {'key': 'fish', 'next': 'w00t!'})]


.. attribute:: Mock.method_calls

    As well as tracking calls to themselves, mocks also track calls to methods and attributes, and *their* methods and attributes:
    
    .. doctest::

        >>> mock = Mock()
        >>> mock.method()
        <mock.Mock object at 0x...>
        >>> mock.property.method.attribute()
        <mock.Mock object at 0x...>
        >>> mock.method_calls
        [('method', (), {}), ('property.method.attribute', (), {})]


-----

.. [#] The only exceptions are magic methods and attributes (those that have leading and trailing double underscores). Mock doesn't create these but instead of raises an ``AttributeError``. This is because the interpreter will often implicitly request these methods, and gets *very* confused to get a new Mock object when it expects a magic method.