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diff --git a/third_party/py/mock/docs/helpers.txt b/third_party/py/mock/docs/helpers.txt new file mode 100644 index 0000000000..571b71d5eb --- /dev/null +++ b/third_party/py/mock/docs/helpers.txt @@ -0,0 +1,583 @@ +========= + Helpers +========= + +.. currentmodule:: mock + +.. testsetup:: + + mock.FILTER_DIR = True + from pprint import pprint as pp + original_dir = dir + def dir(obj): + print pp(original_dir(obj)) + + import urllib2 + __main__.urllib2 = urllib2 + +.. testcleanup:: + + dir = original_dir + mock.FILTER_DIR = True + + + +call +==== + +.. function:: call(*args, **kwargs) + + `call` is a helper object for making simpler assertions, for comparing + with :attr:`~Mock.call_args`, :attr:`~Mock.call_args_list`, + :attr:`~Mock.mock_calls` and :attr: `~Mock.method_calls`. `call` can also be + used with :meth:`~Mock.assert_has_calls`. + + .. doctest:: + + >>> m = MagicMock(return_value=None) + >>> m(1, 2, a='foo', b='bar') + >>> m() + >>> m.call_args_list == [call(1, 2, a='foo', b='bar'), call()] + True + +.. method:: call.call_list() + + For a call object that represents multiple calls, `call_list` + returns a list of all the intermediate calls as well as the + final call. + +`call_list` is particularly useful for making assertions on "chained calls". A +chained call is multiple calls on a single line of code. This results in +multiple entries in :attr:`~Mock.mock_calls` on a mock. Manually constructing +the sequence of calls can be tedious. + +:meth:`~call.call_list` can construct the sequence of calls from the same +chained call: + +.. doctest:: + + >>> m = MagicMock() + >>> m(1).method(arg='foo').other('bar')(2.0) + <MagicMock name='mock().method().other()()' id='...'> + >>> kall = call(1).method(arg='foo').other('bar')(2.0) + >>> kall.call_list() + [call(1), + call().method(arg='foo'), + call().method().other('bar'), + call().method().other()(2.0)] + >>> m.mock_calls == kall.call_list() + True + +.. _calls-as-tuples: + +A `call` object is either a tuple of (positional args, keyword args) or +(name, positional args, keyword args) depending on how it was constructed. When +you construct them yourself this isn't particularly interesting, but the `call` +objects that are in the :attr:`Mock.call_args`, :attr:`Mock.call_args_list` and +:attr:`Mock.mock_calls` attributes can be introspected to get at the individual +arguments they contain. + +The `call` objects in :attr:`Mock.call_args` and :attr:`Mock.call_args_list` +are two-tuples of (positional args, keyword args) whereas the `call` objects +in :attr:`Mock.mock_calls`, along with ones you construct yourself, are +three-tuples of (name, positional args, keyword args). + +You can use their "tupleness" to pull out the individual arguments for more +complex introspection and assertions. The positional arguments are a tuple +(an empty tuple if there are no positional arguments) and the keyword +arguments are a dictionary: + +.. doctest:: + + >>> m = MagicMock(return_value=None) + >>> m(1, 2, 3, arg='one', arg2='two') + >>> kall = m.call_args + >>> args, kwargs = kall + >>> args + (1, 2, 3) + >>> kwargs + {'arg2': 'two', 'arg': 'one'} + >>> args is kall[0] + True + >>> kwargs is kall[1] + True + + >>> m = MagicMock() + >>> m.foo(4, 5, 6, arg='two', arg2='three') + <MagicMock name='mock.foo()' id='...'> + >>> kall = m.mock_calls[0] + >>> name, args, kwargs = kall + >>> name + 'foo' + >>> args + (4, 5, 6) + >>> kwargs + {'arg2': 'three', 'arg': 'two'} + >>> name is m.mock_calls[0][0] + True + + +create_autospec +=============== + +.. function:: create_autospec(spec, spec_set=False, instance=False, **kwargs) + + Create a mock object using another object as a spec. Attributes on the + mock will use the corresponding attribute on the `spec` object as their + spec. + + Functions or methods being mocked will have their arguments checked to + ensure that they are called with the correct signature. + + If `spec_set` is `True` then attempting to set attributes that don't exist + on the spec object will raise an `AttributeError`. + + If a class is used as a spec then the return value of the mock (the + instance of the class) will have the same spec. You can use a class as the + spec for an instance object by passing `instance=True`. The returned mock + will only be callable if instances of the mock are callable. + + `create_autospec` also takes arbitrary keyword arguments that are passed to + the constructor of the created mock. + +See :ref:`auto-speccing` for examples of how to use auto-speccing with +`create_autospec` and the `autospec` argument to :func:`patch`. + + +ANY +=== + +.. data:: ANY + +Sometimes you may need to make assertions about *some* of the arguments in a +call to mock, but either not care about some of the arguments or want to pull +them individually out of :attr:`~Mock.call_args` and make more complex +assertions on them. + +To ignore certain arguments you can pass in objects that compare equal to +*everything*. Calls to :meth:`~Mock.assert_called_with` and +:meth:`~Mock.assert_called_once_with` will then succeed no matter what was +passed in. + +.. doctest:: + + >>> mock = Mock(return_value=None) + >>> mock('foo', bar=object()) + >>> mock.assert_called_once_with('foo', bar=ANY) + +`ANY` can also be used in comparisons with call lists like +:attr:`~Mock.mock_calls`: + +.. doctest:: + + >>> m = MagicMock(return_value=None) + >>> m(1) + >>> m(1, 2) + >>> m(object()) + >>> m.mock_calls == [call(1), call(1, 2), ANY] + True + + + +FILTER_DIR +========== + +.. data:: FILTER_DIR + +`FILTER_DIR` is a module level variable that controls the way mock objects +respond to `dir` (only for Python 2.6 or more recent). The default is `True`, +which uses the filtering described below, to only show useful members. If you +dislike this filtering, or need to switch it off for diagnostic purposes, then +set `mock.FILTER_DIR = False`. + +With filtering on, `dir(some_mock)` shows only useful attributes and will +include any dynamically created attributes that wouldn't normally be shown. +If the mock was created with a `spec` (or `autospec` of course) then all the +attributes from the original are shown, even if they haven't been accessed +yet: + +.. doctest:: + + >>> dir(Mock()) + ['assert_any_call', + 'assert_called_once_with', + 'assert_called_with', + 'assert_has_calls', + 'attach_mock', + ... + >>> import urllib2 + >>> dir(Mock(spec=urllib2)) + ['AbstractBasicAuthHandler', + 'AbstractDigestAuthHandler', + 'AbstractHTTPHandler', + 'BaseHandler', + ... + +Many of the not-very-useful (private to `Mock` rather than the thing being +mocked) underscore and double underscore prefixed attributes have been +filtered from the result of calling `dir` on a `Mock`. If you dislike this +behaviour you can switch it off by setting the module level switch +`FILTER_DIR`: + +.. doctest:: + + >>> import mock + >>> mock.FILTER_DIR = False + >>> dir(mock.Mock()) + ['_NonCallableMock__get_return_value', + '_NonCallableMock__get_side_effect', + '_NonCallableMock__return_value_doc', + '_NonCallableMock__set_return_value', + '_NonCallableMock__set_side_effect', + '__call__', + '__class__', + ... + +Alternatively you can just use `vars(my_mock)` (instance members) and +`dir(type(my_mock))` (type members) to bypass the filtering irrespective of +`mock.FILTER_DIR`. + + +mock_open +========= + +.. function:: mock_open(mock=None, read_data=None) + + A helper function to create a mock to replace the use of `open`. It works + for `open` called directly or used as a context manager. + + The `mock` argument is the mock object to configure. If `None` (the + default) then a `MagicMock` will be created for you, with the API limited + to methods or attributes available on standard file handles. + + `read_data` is a string for the `read` method of the file handle to return. + This is an empty string by default. + +Using `open` as a context manager is a great way to ensure your file handles +are closed properly and is becoming common:: + + with open('/some/path', 'w') as f: + f.write('something') + +The issue is that even if you mock out the call to `open` it is the +*returned object* that is used as a context manager (and has `__enter__` and +`__exit__` called). + +Mocking context managers with a :class:`MagicMock` is common enough and fiddly +enough that a helper function is useful. + +.. doctest:: + + >>> from mock import mock_open + >>> m = mock_open() + >>> with patch('__main__.open', m, create=True): + ... with open('foo', 'w') as h: + ... h.write('some stuff') + ... + >>> m.mock_calls + [call('foo', 'w'), + call().__enter__(), + call().write('some stuff'), + call().__exit__(None, None, None)] + >>> m.assert_called_once_with('foo', 'w') + >>> handle = m() + >>> handle.write.assert_called_once_with('some stuff') + +And for reading files: + +.. doctest:: + + >>> with patch('__main__.open', mock_open(read_data='bibble'), create=True) as m: + ... with open('foo') as h: + ... result = h.read() + ... + >>> m.assert_called_once_with('foo') + >>> assert result == 'bibble' + + +.. _auto-speccing: + +Autospeccing +============ + +Autospeccing is based on the existing `spec` feature of mock. It limits the +api of mocks to the api of an original object (the spec), but it is recursive +(implemented lazily) so that attributes of mocks only have the same api as +the attributes of the spec. In addition mocked functions / methods have the +same call signature as the original so they raise a `TypeError` if they are +called incorrectly. + +Before I explain how auto-speccing works, here's why it is needed. + +`Mock` is a very powerful and flexible object, but it suffers from two flaws +when used to mock out objects from a system under test. One of these flaws is +specific to the `Mock` api and the other is a more general problem with using +mock objects. + +First the problem specific to `Mock`. `Mock` has two assert methods that are +extremely handy: :meth:`~Mock.assert_called_with` and +:meth:`~Mock.assert_called_once_with`. + +.. doctest:: + + >>> mock = Mock(name='Thing', return_value=None) + >>> mock(1, 2, 3) + >>> mock.assert_called_once_with(1, 2, 3) + >>> mock(1, 2, 3) + >>> mock.assert_called_once_with(1, 2, 3) + Traceback (most recent call last): + ... + AssertionError: Expected to be called once. Called 2 times. + +Because mocks auto-create attributes on demand, and allow you to call them +with arbitrary arguments, if you misspell one of these assert methods then +your assertion is gone: + +.. code-block:: pycon + + >>> mock = Mock(name='Thing', return_value=None) + >>> mock(1, 2, 3) + >>> mock.assret_called_once_with(4, 5, 6) + +Your tests can pass silently and incorrectly because of the typo. + +The second issue is more general to mocking. If you refactor some of your +code, rename members and so on, any tests for code that is still using the +*old api* but uses mocks instead of the real objects will still pass. This +means your tests can all pass even though your code is broken. + +Note that this is another reason why you need integration tests as well as +unit tests. Testing everything in isolation is all fine and dandy, but if you +don't test how your units are "wired together" there is still lots of room +for bugs that tests might have caught. + +`mock` already provides a feature to help with this, called speccing. If you +use a class or instance as the `spec` for a mock then you can only access +attributes on the mock that exist on the real class: + +.. doctest:: + + >>> import urllib2 + >>> mock = Mock(spec=urllib2.Request) + >>> mock.assret_called_with + Traceback (most recent call last): + ... + AttributeError: Mock object has no attribute 'assret_called_with' + +The spec only applies to the mock itself, so we still have the same issue +with any methods on the mock: + +.. code-block:: pycon + + >>> mock.has_data() + <mock.Mock object at 0x...> + >>> mock.has_data.assret_called_with() + +Auto-speccing solves this problem. You can either pass `autospec=True` to +`patch` / `patch.object` or use the `create_autospec` function to create a +mock with a spec. If you use the `autospec=True` argument to `patch` then the +object that is being replaced will be used as the spec object. Because the +speccing is done "lazily" (the spec is created as attributes on the mock are +accessed) you can use it with very complex or deeply nested objects (like +modules that import modules that import modules) without a big performance +hit. + +Here's an example of it in use: + +.. doctest:: + + >>> import urllib2 + >>> patcher = patch('__main__.urllib2', autospec=True) + >>> mock_urllib2 = patcher.start() + >>> urllib2 is mock_urllib2 + True + >>> urllib2.Request + <MagicMock name='urllib2.Request' spec='Request' id='...'> + +You can see that `urllib2.Request` has a spec. `urllib2.Request` takes two +arguments in the constructor (one of which is `self`). Here's what happens if +we try to call it incorrectly: + +.. doctest:: + + >>> req = urllib2.Request() + Traceback (most recent call last): + ... + TypeError: <lambda>() takes at least 2 arguments (1 given) + +The spec also applies to instantiated classes (i.e. the return value of +specced mocks): + +.. doctest:: + + >>> req = urllib2.Request('foo') + >>> req + <NonCallableMagicMock name='urllib2.Request()' spec='Request' id='...'> + +`Request` objects are not callable, so the return value of instantiating our +mocked out `urllib2.Request` is a non-callable mock. With the spec in place +any typos in our asserts will raise the correct error: + +.. doctest:: + + >>> req.add_header('spam', 'eggs') + <MagicMock name='urllib2.Request().add_header()' id='...'> + >>> req.add_header.assret_called_with + Traceback (most recent call last): + ... + AttributeError: Mock object has no attribute 'assret_called_with' + >>> req.add_header.assert_called_with('spam', 'eggs') + +In many cases you will just be able to add `autospec=True` to your existing +`patch` calls and then be protected against bugs due to typos and api +changes. + +As well as using `autospec` through `patch` there is a +:func:`create_autospec` for creating autospecced mocks directly: + +.. doctest:: + + >>> import urllib2 + >>> mock_urllib2 = create_autospec(urllib2) + >>> mock_urllib2.Request('foo', 'bar') + <NonCallableMagicMock name='mock.Request()' spec='Request' id='...'> + +This isn't without caveats and limitations however, which is why it is not +the default behaviour. In order to know what attributes are available on the +spec object, autospec has to introspect (access attributes) the spec. As you +traverse attributes on the mock a corresponding traversal of the original +object is happening under the hood. If any of your specced objects have +properties or descriptors that can trigger code execution then you may not be +able to use autospec. On the other hand it is much better to design your +objects so that introspection is safe [#]_. + +A more serious problem is that it is common for instance attributes to be +created in the `__init__` method and not to exist on the class at all. +`autospec` can't know about any dynamically created attributes and restricts +the api to visible attributes. + +.. doctest:: + + >>> class Something(object): + ... def __init__(self): + ... self.a = 33 + ... + >>> with patch('__main__.Something', autospec=True): + ... thing = Something() + ... thing.a + ... + Traceback (most recent call last): + ... + AttributeError: Mock object has no attribute 'a' + +There are a few different ways of resolving this problem. The easiest, but +not necessarily the least annoying, way is to simply set the required +attributes on the mock after creation. Just because `autospec` doesn't allow +you to fetch attributes that don't exist on the spec it doesn't prevent you +setting them: + +.. doctest:: + + >>> with patch('__main__.Something', autospec=True): + ... thing = Something() + ... thing.a = 33 + ... + +There is a more aggressive version of both `spec` and `autospec` that *does* +prevent you setting non-existent attributes. This is useful if you want to +ensure your code only *sets* valid attributes too, but obviously it prevents +this particular scenario: + +.. doctest:: + + >>> with patch('__main__.Something', autospec=True, spec_set=True): + ... thing = Something() + ... thing.a = 33 + ... + Traceback (most recent call last): + ... + AttributeError: Mock object has no attribute 'a' + +Probably the best way of solving the problem is to add class attributes as +default values for instance members initialised in `__init__`. Note that if +you are only setting default attributes in `__init__` then providing them via +class attributes (shared between instances of course) is faster too. e.g. + +.. code-block:: python + + class Something(object): + a = 33 + +This brings up another issue. It is relatively common to provide a default +value of `None` for members that will later be an object of a different type. +`None` would be useless as a spec because it wouldn't let you access *any* +attributes or methods on it. As `None` is *never* going to be useful as a +spec, and probably indicates a member that will normally of some other type, +`autospec` doesn't use a spec for members that are set to `None`. These will +just be ordinary mocks (well - `MagicMocks`): + +.. doctest:: + + >>> class Something(object): + ... member = None + ... + >>> mock = create_autospec(Something) + >>> mock.member.foo.bar.baz() + <MagicMock name='mock.member.foo.bar.baz()' id='...'> + +If modifying your production classes to add defaults isn't to your liking +then there are more options. One of these is simply to use an instance as the +spec rather than the class. The other is to create a subclass of the +production class and add the defaults to the subclass without affecting the +production class. Both of these require you to use an alternative object as +the spec. Thankfully `patch` supports this - you can simply pass the +alternative object as the `autospec` argument: + +.. doctest:: + + >>> class Something(object): + ... def __init__(self): + ... self.a = 33 + ... + >>> class SomethingForTest(Something): + ... a = 33 + ... + >>> p = patch('__main__.Something', autospec=SomethingForTest) + >>> mock = p.start() + >>> mock.a + <NonCallableMagicMock name='Something.a' spec='int' id='...'> + +.. note:: + + An additional limitation (currently) with `autospec` is that unbound + methods on mocked classes *don't* take an "explicit self" as the first + argument - so this usage will fail with `autospec`. + + .. doctest:: + + >>> class Foo(object): + ... def foo(self): + ... pass + ... + >>> Foo.foo(Foo()) + >>> MockFoo = create_autospec(Foo) + >>> MockFoo.foo(MockFoo()) + Traceback (most recent call last): + ... + TypeError: <lambda>() takes exactly 1 argument (2 given) + + The reason is that its very hard to tell the difference between functions, + unbound methods and staticmethods across Python 2 & 3 and the alternative + implementations. This restriction may be fixed in future versions. + + +------ + +.. [#] This only applies to classes or already instantiated objects. Calling + a mocked class to create a mock instance *does not* create a real instance. + It is only attribute lookups - along with calls to `dir` - that are done. A + way round this problem would have been to use `getattr_static + <http://docs.python.org/dev/library/inspect.html#inspect.getattr_static>`_, + which can fetch attributes without triggering code execution. Descriptors + like `classmethod` and `staticmethod` *need* to be fetched correctly though, + so that their signatures can be mocked correctly. |