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Python: setting default side_effect with create_autospec on class instance

I am trying to use side_effect with unittest.mock.create_autospec on class to set default instance call behavior to raise NotImplementedError.
The problem I am facing is:
I do not want exception to be raise on class __init__.
I do not want to set explicitly all my methods side effect.
I want to use a pytest.fixture in order to make my mock reusable through various tests.
Here a code sample of what I am trying to achieve.
# module.py
class MyClass:
def __init__(self, value):
self.value = value
def compute(self):
return self.value
def foo():
instance = MyClass(42)
return instance.compute()
# test_module.py
from unittest.mock import create_autospec
import module
import pytest
#pytest.fixture(autouse=True)
def my_class(monkeypatch):
# Help me HERE to set side_effect, bellow tests will not work with this settings.
spec_cls = create_autospec(module.MyClass, side_effect=NotImplementedError)
monkeypatch.setattr(module, "MyClass", spec_cls)
return spec_cls("<whatever>")
def test_foo():
with pytest.raises(NotImplementedError):
module.foo()
def test_bar(my_class):
my_class.compute.return_value = 24
assert module.foo() == 24

Not need to use autospec :
import unittest.mock as mocking
import pytest
import so71018132_module as module
#pytest.fixture(autouse=True)
def fake_my_class():
with mocking.patch.object(module.MyClass, "compute") as compute_mock:
compute_mock.side_effect = NotImplementedError # default behaviour
yield compute_mock
def test_foo():
with pytest.raises(NotImplementedError):
module.foo()
def test_bar(fake_my_class):
fake_my_class.side_effect = [24]
# or alternatively, clear the side_effect then set a return_value :
# fake_my_class.side_effect = None
# fake_my_class.return_value = 24
assert module.foo() == 24
passes the 2 tests.
I completely changed the fixture to use unittest.mock.object.patch on the compute method of MyClass so just that is mocked, the rest of the class is used ordinarily.
Also, I had to slightly adjust the test_bar code to correctly alter the mock behavior.

Python: is it possible to wrap "#patch(path)" for re-use? (unittest)

As the doc "Where to patch" says, we need to patch where an object is looked up, (not where it's defined); so I understand that it's not possible to - let's say - create a reusable patch for a particular path
Imagine you have several modules importing an object you'd like to mock
# file_a.py
from foo.goo.hoo import settings
# file_b.py
from foo.goo.hoo import settings
# file_c.py
from foo.goo.hoo import settings
I was wondering if there is a way to create a decorator such as:
#mock_settings
def test_whatever(self, settings_mock):
...
instead of this solution:
#patch("some_module.file_a.settings")
def test_whatever(self, settings_mock):
...
#patch("some_module.file_b.settings")
def test_whatever(self, settings_mock):
...
#patch("some_module.file_c.settings")
def test_whatever(self, settings_mock):
...

As mentioned in the question, to patch an object you have to patch its reference in the module to be tested (in case it is imported using from ...import).
To have it patched in several modules, you can patch all of these modules with the same mock, and use that mock. If you know in advance which modules you want to patch, you can just do this. If you don't know them in advance, you have to try to patch the object in all loaded modules -- this may get a bit more complicated.
I will show an example using pytest and a pytest fixture, as this is more compact; you could wrap that in a decorator for usage in unittest, but that will not change the basics. Consider we have a class that needs to be mocked in several modules:
class_to_mock.py
class ClassToMock:
def foo(self, msg):
return msg
module1.py
from class_to_mock import ClassToMock
def do_something():
inst = ClassToMock()
return inst.foo("module1")
module2.py
from class_to_mock import ClassToMock
def do_something_else():
inst = ClassToMock()
return inst.foo("module2")
You can now write a fixture that mocks the class in all of these modules at once (here using pytest-mock for simplicity):
#pytest.fixture
def mocked_class(mocker):
mocked = Mock()
for module in ('module1', 'module2'):
mocker.patch(module + '.ClassToMock', mocked)
yield mocked
This can be used to test both modules:
def test_module1(mocked_class):
mocked_class.return_value.foo.return_value = 'mocked!'
assert module1.do_something() == 'mocked!'
def test_module2(mocked_class):
mocked_class.return_value.foo.return_value = 'mocked!'
assert module2.do_something_else() == 'mocked!'
If you want a generic version that mocks the class in all loaded modules, you can replace the fixture with something like this:
#pytest.fixture
def mocked_class(mocker):
mocked = Mock()
for name, module in list(sys.modules.items()):
if not inspect.ismodule(module):
continue
for cls_name, cls in module.__dict__.items():
try: # need that as inspect may raise for some modules
if inspect.isclass(cls) and cls_name == "ClassToMock":
mocker.patch(name + ".ClassToMock", mocked)
except Exception:
continue
yield mocked
This will work for this specific example - to generalize this, it has to consider more object types, the class shall be configurable, and there may be some more issues - opposed to the more simple version where you just enumerate the modules you want to patch, which will always work.
You could do something similar in unittest.setUp by putting the mock in an instance variable, though that is less elegant, because you are also responsible for stopping the mocking:
class ModulesTest(unittest.TestCase):
def setUp(self):
self.mocked_class = Mock()
self.mocks = []
for module in ('module1', 'module2'):
mocked = mock.patch(module + '.ClassToMock', self.mocked_class)
self.mocks.append(mocked)
mocked.start()
def tearDown(self):
for mocked in self.mocks:
mocked.stop()
def test_module1(self):
self.mocked_class.return_value.foo.return_value = 'mocked!'
assert module1.do_something() == 'mocked!'
And you can also wrap this in a decorator, to answer your original question at least partially:
def mocked_class_to_mock(f):
#wraps(f)
def _mocked_class_to_mock(*args, **kwargs):
mocked_class = Mock()
mocks = []
for module in ('module1', 'module2'):
mocked = mock.patch(module + '.ClassToMock', mocked_class)
mocks.append(mocked)
mocked.start()
kwargs['mocked_class'] = mocked_class # use a keyword arg for simplicity
f(*args, **kwargs)
for mocked in mocks:
mocked.stop()
return _mocked_class_to_mock
...
#mocked_class_to_mock
def test_module3(self, mocked_class):
mocked_class.return_value.foo.return_value = 'mocked!'
assert module3.do_something() == 'mocked!'
Of course, you can do the same with the more generic version, if needed.
Also note that I skipped the simpler case where the object is imported using import .... In this case, you have to patch the original module. In the generic fixture, you probably want to add that case always.

Python mock a method when specific argument

I have a python method like
import external_object
from external_lib1 import ExternalClass1
from external_lib2 import Hook
class MyClass(self):
def my_method(self):
ExternalClass.get('arg1') #should be mocked and return a specific value with this arg1
ExternalClass.get('arg2') #should be mocked and return a specific value with this arg2
def get_hook(self):
return Hook() # return a mock object with mocked method on it
def my_method(self):
object_1 = external_object.instance_type_1('args') # those are two different object instanciate from the same lib.
object_2 = external_object.instance_type_2('args')
object_1.method_1('arg') # should return what I want when object_1 mocked
object_2.method_2 ('arg') # should return what I want when object_2 mocked
In my test I would like to realise what I put in comments.
I could manage to do it, but every time it gets really messy.
I use to call flexmock for some stuff (by example ExternalClass.get('arg1') would be mock with a flexmock(ExternalClass).should_return('arg').with_args('arg') # etc...) but I'm tired of using different test libs to mock.
I would like to use only the mock library but I struggle to find a consistent way of doing it.

I like to use python's unittest lib. Concretely the unittest.mock which is a great lib to customize side effects and return value in unit tested functions.
They can be used as follows:
class Some(object):
"""
You want to test this class
external_lib is an external component we cannot test
"""
def __init__(self, external_lib):
self.lib = external_lib
def create_index(self, unique_index):
"""
Create an index.
"""
try:
self.lib.create(index=unique_index) # mock this
return True
except MyException as e:
self.logger.error(e.__dict__, color="red")
return False
class MockLib():
pass
class TestSome(unittest.TestCase):
def setUp(self):
self.lib = MockLib()
self.some = Some(self.lib)
def test_create_index(self):
# This will test the method returns True if everything went fine
self.some.create_index = MagicMock(return_value={})
self.assertTrue(self.some.create_index("test-index"))
def test_create_index_fail(self):
# This will test the exception is handled and return False
self.some.create_index = MagicMock(side_effect=MyException("error create"))
self.assertFalse(self.some.create_index("test-index"))
Put the TestSome() class file somewhere like your-codebase-path/tests and run:
python -m unittest -v
I hope it's useful.

How to share object from fixture to all tests using pytest?

What is the best way to define an object in a fixture with session scope and autouse=True, so it will be available to all tests?
#pytest.fixture(scope='session', autouse=True)
def setup_func(request):
obj = SomeObj()
Next thing, I want some magic that previously created obj will appear in each test context without the need of each test to define the setup_func fixture.
def test_one():
obj.do_something_fancy()

My recommendation would to add the fixture to conftest.py and make sure to return the object you want to produce from the fixture.
As noted, this makes "autouse" kind of useless.
In the root directory for your tests, add the fixture to a file named conftest.py:
#pytest.fixture(scope='session', autouse=True)
def someobj(request):
return SomeObj()
Any test file beneath the root file will have access to this fixture (for example test_foo.py):
def test_foo(someobj):
assert isinstance(someobj, SomeObj)
Another approach, would be to use a global variable defined in the same test or imported from a module.
For example in conftest.py:
someobj = None
#pytest.fixture(scope='session', autouse=True)
def prep_someobj(request):
someobj = SomeObj()
Then in your test:
from . import conftest
def test_foo():
assert isinstance(conftest.someobj, SomeObj)
In my opinion this is less readable and more cumbersome than the first method.

A more general pattern for this is to return locals() at the end of your conftest and you'll be able to easily reference anything created in the fixture.
conftest.py
#pytest.fixture(scope='session')
def setup_func(request):
obj1 = SomeObj()
obj2 = SomeObj()
return locals()
test_stuff.py
def test_one(setup_func):
setup_func['obj1'].do_something_fancy()
def test_two(setup_func):
setup_func['obj2'].do_something_fancy()

Another possibility is to wrap your tests in a class and use class variables to only define the object instance once. This assumes you are able to wrap all tests in a single class and so this answer may address a less general, but similar use case. For example,
class SomeObj():
"""This object definition may exist in another module and be imported."""
def __init__(self):
self.x = 5
def do_something_fancy(self, y):
return self.x * y
class TestX():
# Object instance to share across tests
someobj = SomeObj()
def test_x(self):
assert TestX.someobj.x == 5
def test_fancy(self):
fancy_factor = 10
result = TestX.someobj.do_something_fancy(fancy_factor)
assert result == 50

Append the nose #attr to the test name

I am able to setup nose tests to run with the #attr tag. I am now interested in know if I can append to the end of the test name, the #attr tag? What we are trying to do is add a tag if our tests run into an issue and we write up a defect for it, we would then put the defect number as an #attr tag. Then when we run we could easily identify which tests have open defects against them.
Just wondering if this is even possible, and where to go to see how to set it up?
EDIT RESULTS RUNNING WITH ANSWER:
Test Results:
So I sort of know what is going on, if I have the #fancyattr() at the class level it picks it up and changes the name of the class. When I put the #fancyattr() at the test level it is not changing the name of the test, which is what I need for it to do.
For example - Changes the name of the class:
#dms_attr('DMSTEST')
#attr('smoke_login', 'smoketest', priority=1)
class TestLogins(BaseSmoke):
"""
Just logs into the system and then logs off
"""
def setUp(self):
BaseSmoke.setUp(self)
def test_login(self):
print u"I can login -- taking a nap now"
sleep(5)
print u"Getting off now"
def tearDown(self):
BaseSmoke.tearDown(self)
This is what I need and it isn't working:
#attr('smoke_login', 'smoketest', priority=1)
class TestLogins(BaseSmoke):
"""
Just logs into the system and then logs off
"""
def setUp(self):
BaseSmoke.setUp(self)
#dms_attr('DMSTEST')
def test_login(self):
print u"I can login -- taking a nap now"
sleep(5)
print u"Getting off now"
def tearDown(self):
BaseSmoke.tearDown(self)
Updated screenshot with what I am seeing with __doc__:

Here is how to do it with args type attributes:
rename_test.py:
import unittest
from nose.tools import set_trace
def fancy_attr(*args, **kwargs):
"""Decorator that adds attributes to classes or functions
for use with the Attribute (-a) plugin. It also renames functions!
"""
def wrap_ob(ob):
for name in args:
setattr(ob, name, True)
#using __doc__ instead of __name__ works for class methods tests
ob.__doc__ = '_'.join([ob.__name__, name])
#ob.__name__ = '_'.join([ob.__name__, name])
return ob
return wrap_ob
class TestLogins(unittest.TestCase):
#fancy_attr('slow')
def test_method():
assert True
#fancy_attr('slow')
def test_func():
assert True
Running test:
$ nosetests rename_test.py -v
test_method_slow ... ok
test_func_slow ... ok
----------------------------------------------------------------------
Ran 2 tests in 0.003s
OK
EDIT: For xunit reporting to work, test renaming should take place before running the test. You can do it on import, here is untested hack showing how to do it:
rename_test.py:
import unittest
def fancy_attr(*args, **kwargs):
"""Decorator that adds attributes to classes or functions
for use with the Attribute (-a) plugin. It also renames functions!
"""
def wrap_ob(ob):
for name in args:
setattr(ob, name, True)
ob.__doc__ = '_'.join([ob.__name__, name])
return ob
return wrap_ob
class TestLogins(unittest.TestCase):
#fancy_attr('slow')
def test_method(self):
assert True
def make_name(orig, attrib):
return '_'.join([orig, attrib])
def rename(cls):
methods = []
for key in cls.__dict__:
method = getattr(cls, key)
if method:
if hasattr(cls.__dict__[key], '__dict__'):
if 'slow' in cls.__dict__[key].__dict__:
methods.append(key)
print methods
for method in methods:
setattr(cls, make_name(method, 'slow'), cls.__dict__[key])
delattr(cls, method)
rename(TestLogins)
#fancy_attr('slow')
def test_func():
assert True