Mocking a Django Queryset in order to test a function that takes a queryset

Question

I have a utility function in my Django project, it takes a queryset, gets some data from it and returns a result. I\'d like to write some tests for this function. Is there a

Answer 1

Not that I know of, but why not use an actual queryset? The test framework is all set up to allow you to create sample data within your test, and the database is re-created on every test, so there doesn't seem to be any reason not to use the real thing.

Answer 2

One first advice would be to split the function in two parts, one that creates the queryset and one that manipulates the output of it. In this way testing the second part is straightforward.

For the database problem, I investigated if django uses sqlite-in-memory and I found out that recent version of django uses the sqlite -in-memory database, from The django unittest page:

When using the SQLite database engine the tests will by default use an in-memory database (i.e., the database will be created in memory, bypassing the filesystem entirely!).

Mocking the QuerySet object will not make you exercise its full logic.

Answer 3

Try out the django_mock_queries library that lets you mock out the database access, and still use some of the Django query set features like filtering.

Full disclosure: I contributed some features to the project.

Answer 4

Of course you can mock a QuerySet, you can mock anything.

You can create an object yourself, and give it the interface you need, and have it return any data you like. At heart, mocking is nothing more than providing a "test double" that acts enough like the real thing for your tests' purposes.

The low-tech way to get started is to define an object:

class MockQuerySet(object):
    pass

then create one of these, and hand it to your test. The test will fail, likely on an AttributeError. That will tell you what you need to implement on your MockQuerySet. Repeat until your object is rich enough for your tests.

Answer 5

Have you looked into FactoryBoy? https://factoryboy.readthedocs.io/en/latest/orms.html It's a fixtures replacement tool with support for the django orm - factories basically generate orm-like objects (either in memory or in a test database).

Here's a great article for getting started: https://www.caktusgroup.com/blog/2013/07/17/factory-boy-alternative-django-testing-fixtures/

Answer 6

I am having the same issue, and it looks like some nice person has written a library for mocking QuerySets, it is called mock-django and the specific code you will need is here https://github.com/dcramer/mock-django/blob/master/mock_django/query.py I think you can then just patch you models objects function to return one of these QuerySetMock objects that you have set up to return something expected!