pytest-django-filefield

Patch the storage of your models' FileFields effortlessly.
Best served with pytest-django and your own fixtures.

Install and enable the plugin:

pip install pytest-django-filefield

Roll your fixture:

# conftest.py
from django.core.files import storage
from django.db import models

@pytest.fixture
def fake_storage(monkeypatch, tmp_path) 
    storage = storage.FileSystemStorage(location=tmp_path)
    monkeypatch.setattr(models.FileField, "storage", storage)
    return storage

Have it scoped however you want, or just mark as autouse=True and forget about it.

This simple hack is packaged as a pytest plugin to make it work with pytest-django, because there is no simpler way to inject custom code before it calls django.setup().

Do I even need this?

There's a good chance that you don't! But let's first recap on some of the ways to patch the storage, given a model somewhat like below:

class Contract(models.Model):
    document = models.FileField(storage=DocumentStorage())

Just patch the field

storage is an instance attribute of each FileField, so the most straightforward and robust way would be to just find the field instance and patch the attribute:

def test_document_upload(monkeypatch, my_fake_storage):
    document_field = Contract._meta.get_field_by_name("document")[0]
    monkeypatch.setattr(document_field, "storage", my_fake_storage)

    upload_contract_document()

    assert_results(my_fake_storage)

The requirement here is that you know which fields of which models should be patched, and make sure to get it right for corresponding tests. This could become quite noisy and/or tedious to maintain. However, the approach is beneficial if there is quite a number of different storages, especially different storages used within the same model.

If the project uses a single storage for everything, or just a handful of them, such flexibility might be overkill.

Define a different storage for tests

Extract the name of the storage class into settings.py, use a different settings file for tests (which you should anyway) with a different value there. This way the storage is replaced before Django is even initialized.

# settings.py
DOCUMENT_STORAGE = 'myapp.storages.DocumentStorage'

# settings_test.py
DOCUMENT_STORAGE = 'myapp.tests.storages.FakeDocumentStorage'

# models.py
class Contract(models.Model):
    document = models.FileField(
        storage=import_string(settings.DOCUMENT_STORAGE)()
    )

# tests/test_contract.py
def test_document_upload():
    document_field = Contract._meta.get_field_by_name("document")[0]

    upload_contract_document()

    assert_results(document_field.storage)

Patching not required, each field still has its own instance of a test storage, but all the objects using that field share the same storage for the whole test session. Which is already good enough and you may just stop here!

Patch all the storages, with configurable scope

This is what the plugin enables. It replaces FileField().storage, which is normally an instance attribute, with a property of the same name. A property is defined in a class, so this forces all the "storage" attribute lookups to be done on a class. You now don't have to hunt down every FileField instance and can just patch the class property instead.

The drawback is that any and all FileFields are patched for duration of the fixture's scope. Since the narrowest scope is function, this may (only) be a problem if a single test needs to check the behaviours of multiple storages in isolation.

Summary

As always, choose what works best for your specific project!