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=======
Remarks
=======
Type annotations
----------------
``pytest-mock`` is fully type annotated, letting users use static type checkers to
test their code.
The ``mocker`` fixture returns ``pytest_mock.MockerFixture`` which can be used
to annotate test functions:
.. code-block:: python
from pytest_mock import MockerFixture
def test_foo(mocker: MockerFixture) -> None:
...
The type annotations have been checked with ``mypy``, which is the only
type checker supported at the moment; other type-checkers might work
but are not currently tested.
Why bother with a plugin?
=========================
There are a number of different ``patch`` usages in the standard ``mock`` API,
but IMHO they don't scale very well when you have more than one or two
patches to apply.
It may lead to an excessive nesting of ``with`` statements, breaking the flow
of the test:
.. code-block:: python
import mock
def test_unix_fs():
with mock.patch('os.remove'):
UnixFS.rm('file')
os.remove.assert_called_once_with('file')
with mock.patch('os.listdir'):
assert UnixFS.ls('dir') == expected
# ...
with mock.patch('shutil.copy'):
UnixFS.cp('src', 'dst')
# ...
One can use ``patch`` as a decorator to improve the flow of the test:
.. code-block:: python
@mock.patch('os.remove')
@mock.patch('os.listdir')
@mock.patch('shutil.copy')
def test_unix_fs(mocked_copy, mocked_listdir, mocked_remove):
UnixFS.rm('file')
os.remove.assert_called_once_with('file')
assert UnixFS.ls('dir') == expected
# ...
UnixFS.cp('src', 'dst')
# ...
But this poses a few disadvantages:
- test functions must receive the mock objects as parameter, even if you don't plan to
access them directly; also, order depends on the order of the decorated ``patch``
functions;
- receiving the mocks as parameters doesn't mix nicely with pytest's approach of
naming fixtures as parameters, or ``pytest.mark.parametrize``;
- you can't easily undo the mocking during the test execution;
An alternative is to use ``contextlib.ExitStack`` to stack the context managers in a single level of indentation
to improve the flow of the test:
.. code-block:: python
import contextlib
import mock
def test_unix_fs():
with contextlib.ExitStack() as stack:
stack.enter_context(mock.patch('os.remove'))
UnixFS.rm('file')
os.remove.assert_called_once_with('file')
stack.enter_context(mock.patch('os.listdir'))
assert UnixFS.ls('dir') == expected
# ...
stack.enter_context(mock.patch('shutil.copy'))
UnixFS.cp('src', 'dst')
# ...
But this is arguably a little more complex than using ``pytest-mock``.
|
