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    pymox

Python mocking on steroids


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Python mocking on steroids.

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What

Pymox is mocking on steroids. It's a powerful mock object framework for Python, providing many tools to help with your unit tests, so you can write them in an easy, quick and intuitive way.

Why

Why Pymox? Python already has batteries included. It has its own mock library, widely used in Python applications.

So, why pytest, given we have Python's unittest? Why arrow or pendulum given we have Python's datetime? Why X, given we have Python's Y?

You got it 😉!

Coming Soon

  • Async support
  • Decorator
  • Ignore args
  • String imports

How

Install

pip install pymox

Cool Stuff

New Elegant Way

# conftest.py
pytest_plugins = ("mox.testing.pytest_mox",)


# test.py
from mox import expect, stubout


class TestOs:
     def test_getcwd(self):
        with stubout(os, 'getcwd') as m_getcwd, expect:
            m_getcwd.to_be.called_with().and_return('/mox/path')

        assert os.getcwd() == '/mox/path'
        mox.verify(m_getcwd)

If you want to be less verbose:

class TestOs:
     def test_getcwd(self):
        with stubout(os, 'getcwd') as m_getcwd:
            m_getcwd().returns('/mox/path')

        assert os.getcwd() == '/mox/path'
        mox.verify(m_getcwd)

Anything you put inside the context manager is a call expectation, so to not expect any call you can:

class TestOs:
     def test_getcwd(self):
        with stubout(os, 'getcwd') as m_getcwd:
            pass

        # will raise a UnexpectedMethodCallError
        assert os.getcwd() == '/mox/path'
        mox.verify(m_getcwd)

Dict Access

class TestDict:
    def test_dict_access(self):
        config = {'env': 'dev', 'reload': True}

        # doing in another way using create, but you can do with stubout too
        mock_config = mox.create(config)

        mock_config['env'].returns('prod')
        mock_config['reload'].returns(False)

        mox.replay(mock_config)
        assert mock_config['env'] == 'prod'
        assert mock_config['reload'] is False
        mox.verify(mock_config)

Comparators

class Client:
    def get(self, url, params):
        return requests.get(url, params)


class Service:
    def get_contacts(self):
        url = 'https://my.reallylong.service/api/v1/contacts/'
        params = {'added': '7days', 'order_by': '-created'}
        return Client().get(url, params)


class TestSevice:
    def test_get_contacts_comparators_str_and_key_value(self):
        with stubout(Client, 'get') as m_get:
            url = mox.str_contains('/api/v1/contacts')
            params = mox.contains_key_value('added', '7days')
            m_get(url, params).returns({})

        service = Service()
        assert service.get_contacts() == {}
        mox.verify(m_get)

    def test_get_contacts_comparators_and_func_in_is_a(self):
        with stubout(Client, 'get') as m_get:
            url = mox.func(lambda v: str.startswith(v, 'https://my.reallylong.service/'))
            params = mox.and_(
                mox.is_a(dict),
                mox.in_('added'),
            )
            m_get(url, params).returns({})

        service = Service()
        assert service.get_contacts() == {}
        mox.verify(m_get)

    def test_get_contacts_comparators_ignore_arg_not(self):
        with stubout(Client, 'get') as m_get:
            url = mox.ignore_arg()
            params = mox.not_(mox.is_(None))
            m_get(url, params).returns({})

        service = Service()
        assert service.get_contacts() == {}
        mox.verify(m_get)

Other comparators: contains_attribute_value, in_, is_, is_almost, or_, same_elements_as, regex

And Raises

class TestOs:
     def test_getcwd(self):
        with stubout(os, 'getcwd') as m_getcwd:
            # .and_raise(..) also works
            os.getcwd().raises(Exception('error'))

        with pytest.raises(Exception, match='error'):
            os.getcwd()
        mox.verify(m_getcwd)

Multiple Times

class TestOs:
     def test_getcwd(self):
        with stubout(os, 'getcwd') as m_getcwd:
            m_getcwd().returns('/mox/path')
            # the second call will return a different value
            m_getcwd().returns('/mox/another/path')
            # the three subsequent calls will return "/"
            # if no argument is passed, multiple_times doesn't limit the number of calls
            m_getcwd().multiple_times(3).returns('/')

        assert os.getcwd() == '/mox/path'
        assert os.getcwd() == '/mox/another/path'
        mox.verify(m_getcwd)

Any order

If you stub out multiple, the order os calls is enforced, unless you use any_order

class TestOs:
    def test_getcwd(self):
        with stubout.many([os, 'getcwd'], [os, 'cpu_count']) as (m_getcwd, m_cpu_count):
            m_getcwd().returns('/mox/path')
            m_cpu_count().returns('10')

        # will raise a UnexpectedMethodCallError
        assert os.cpu_count() == '10'
        assert os.getcwd() == '/mox/path'
        mox.verify(m_getcwd, m_cpu_count)

    def test_getcwd_anyorder(self):
        with stubout.many([os, 'getcwd'], [os, 'cpu_count']) as (m_getcwd, m_cpu_count):
            m_getcwd().any_order().returns('/mox/path')
            m_cpu_count().any_order().returns('10')

        assert os.cpu_count() == '10'
        assert os.getcwd() == '/mox/path'
        mox.verify(m_getcwd, m_cpu_count)

Remember/Value

The Remember and Value are comparators, but they deserve their own section. They can be useful to retrieve some values from deeper levels of your codebase, and bring to the test for comparison. Let's see an example:

class Handler:
    def modify(self, d):
        # any integer key less than 5 is removed from the dict
        keys_to_remove = [key for key in d if isinstance(key, int) and key < 5]
        for key in keys_to_remove:
            del d[key]
        return d

    def send(self, d):
        return d


class Manager:
    def __init__(self, handlers=None):
        self.handlers = handlers or []

    def process(self, d):
        for handler in self.handlers:
            modified = handler.modify(d)
            handler.send(modified)


class TestManager(mox.MoxTestBase):
    def test_manager_process(self):
        mydict = {1: "apple", 4: "banana", 6: {2: 3, 4: {1: "orange", 7: 8}}, 8: 3}
        myvalue = mox.value()

        with mox.stubout(Handler, 'send') as mock_send:
            # so we use remember in the send call, and its value then the function is
            # called will go to `myvalue`
            mock_send(mox.remember(myvalue))

        Manager([Handler()]).process(mydict)
        mox.verify(mock_send)

        # now we can compare myvalue with what we think its value must be
        assert myvalue == {6: {2: 3, 4: {1: 'orange', 7: 8}}, 8: 3}

Classic Way

import mox
import os

class TestOs:
    def test_getcwd(self):
        m = mox.Mox()

        m.stubout(os, 'getcwd')
        # calls
        os.getcwd().returns('/mox/path')

        m.replay_all()
        assert os.getcwd() == '/mox/path'
        m.verify_all()


if __name__ == '__main__':
    import unittest
    unittest.main()

Jurassic Way

import mox
import os


class TestOs(mox.MoxTestBase):
    def test_getcwd(self):
        self.mox.StubOutWithMock(os, 'getcwd')
        # calls
        os.getcwd().AndReturn('/mox/path')

        self.mox.ReplayAll()
        self.assertEqual(os.getcwd(), '/mox/path')
        self.mox.VerifyAll()


if __name__ == '__main__':
    import unittest
    unittest.main()

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