Mocking API in Python

They said that cool guys test their code. So I have tried. You can find here some samples for quick mocking API in your project.

Quick background

The CUT (class under test - ConsoleClient here) is responsible for handling all logic of my app. It has it's own object to handle communication with API (todoist here).

It works like this:

1. Tell the ConsoleClient that we want to work with our tasks from todoist.
2. ConsoleClient goes to factory class and says, "sup homie?, gimme todoist api handler".
3. All api handlers based on one interface class so ConsoleClient don't has to bother about it anymore.

Logic complicated or not, should has some tests, that's the only way to deliver like a boss... I hope so.

So let's point the problem. First let's assume we want to write test case for ConsoleClient logic only! Imagine some date checking, filtering, printing etc. Second, tests should be fast, we don't want to create client, connect to API etc. We just need to cheet out ConsoleClient and make some dump API handler. Let's do this!

Prepare our api client

As I mentioned, all API clients have common interface, use it! Ladies and gentlemen, the fanciest API client ever below!

class MockedClient(Todo_interface):
    def __init__(self, configuration):
        super().__init__(configuration)

        self.mocked_items = [{
            'id' : i,
            'content' : f'sample_content_{i}',
            'checked' : 1,
            'due' : {
                'date' : datetime.today().strftime('%Y-%m-%d')
                }
            } for i in range(5)]

    def getClient(self):
        pass

    def getItems(self):
        return self.mocked_items

Insert it into code

Here comes the magic you came for. Use decorator @mock.patch.object( Class_we_are_interested_in, "and_its_method_name"). It basically patches the method of class with mock object.

In simple steps based on example below:

1. take ProviderFactory class
2. mock the specified method
3. pass changed ProviderFactory class to setUp method as a mock_client_factory

Now it is showtime for our MockedClient. Specify its instance as a returning value of mocked method and voila! After that, when in init method of ConcoleClient, ProviderFactory.getClientHandler('some client's name') will be triggered, it will return out fantastic mock and use it as API handler later.

from unittest import mock, TestCase

class TestCase(TestCase):
    @mock.patch.object(ProviderFactory, 'getClientHandler')
    def setUp(self, mock_client_factory):
        self.mocked_client = MockedClient( {'some_config': 'value'})
        mock_client_factory.return_value = self.mocked_client

        self.cut = ConsoleClient('todoist')

what you should remember

1. Check the docs for details or if anything fails.
2. Order of decorators and passing them to method.

In python decorators are applied from bottom up. This should correspond to mocked objects you pass to method. Check out example below.

@mock.patch.object( some_class_1 , 'some_method_1')
@mock.patch.object( some_class_2 , 'some_method_2')
def test_blah_blah( self, mock_some_class_2, mock_some_class_1 ):
    ✨✨✨✨✨✨✨
    ✨TEST   MAGIC✨
    ✨✨✨✨✨✨✨