Is there a way to mock a complete bit of code in pytest using mock?

Question

For instance, every time a test finds

database.db.session.using_bind("reader")

I want to remove the using_bind("reader")) and just work with

database.db.session

using mocker

Tried to use it like this in conftest.py

@pytest.fixture(scope='function')
def session(mocker):
    mocker.patch('store.database.db.session.using_bind', return_value=_db.db.session)

But nothing has worked so far.

Code under test:

from store import database     
results = database.db.session.using_bind("reader").query(database.Order.id).join(database.Shop).filter(database.Shop.deleted == False).all(), 

and I get

AttributeError: 'scoped_session' object has no attribute 'using_bind' as an error.

Answer 1

Let's start with an MRE where the code under test uses a fake database:

from unittest.mock import Mock, patch

class Session:
    def using_bind(self, bind):
        raise NotImplementedError(f"Can't bind {bind}")

    def query(self):
        return "success!"


database = Mock()
database.db.session = Session()


def code_under_test():
    return database.db.session.using_bind("reader").query()


def test():
    assert code_under_test() == "success!"

Running this test fails with:

E       NotImplementedError: Can't bind reader

So we want to mock session.using_bind in code_under_test so that it returns session -- that will make our test pass.

We do that using patch, like so:

@patch("test.database.db.session.using_bind")
def test(mock_bind):
    mock_bind.return_value = database.db.session
    assert code_under_test() == "success!"

Note that my code is in a file called test.py, so my patch call applies to the test module -- you will need to adjust this to point to the module under test in your own code.

Note also that I need to set up my mock before calling the code under test.