Clarify how assertQuerysetEqual()'s transform parameter works

[Alexander Todorov]

According to:
​https://docs.djangoproject.com/en/2.0/topics/testing/tools/#django.test.TransactionTestCase.assertQuerysetEqual

Asserts that a queryset qs returns a particular list of values values.

The comparison of the contents of qs and values is performed using the function transform;

The way I read this is that this assert method receives a queryset and a list parameters and compares their contents for equality. By default it will use repr to do that but the user can change this. The way the docs are written suggests that the transform function is applied to both the queryset and the values list. In other words in my tests I can write:

self.assertQuerysetEqual(some_query_taken_from_request_context, [test_object1, test_object2, etc])

The tutorial doesn't use the above but instead hard codes string representations in the tests:
​https://docs.djangoproject.com/en/2.0/intro/tutorial05/#testing-our-new-view

IMO this is less optimal, makes test suites more fragile (dependent on repr()) and less intuitive b/c the expected value isn't a list of the actual objects but a list of their representation which may have been obtained elsewhere.

Note: this may sounds like an RFE but if we trust the docs it's a bug.

Note2: I can contribute a PR for this and update the existing test suite & docs. Just let me know how you feel about it.

[Tim Graham]

As someone who knows how the transform parameter works, the documentation is unclear to me. Changing behavior would be backwards incompatible.

For the use case you mentioned, it would also be useful to recommend assertSequenceEqual(queryset, [obj1, obj2, ...]) and assertCountEqual() as these are simpler than assertQuerysetEqual().

[Jacob Walls]

Hi Shubham Singh, hope it's alright that I submitted a tiny patch for this.

​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In 659a73bc:

Fixed #29308 -- Clarified how assertQuerysetEqual()'s transform works.

[Mariusz Felisiak <felisiak.mariusz@…>]

In eae78a3:

[3.1.x] Fixed #29308 -- Clarified how assertQuerysetEqual()'s transform works.

Backport of 659a73bc0a2df9be856e23fcfc6cc66d0d1a35fd from master

[Mariusz Felisiak <felisiak.mariusz@…>]

In 9141841c:

[3.0.x] Fixed #29308 -- Clarified how assertQuerysetEqual()'s transform works.

Backport of 659a73bc0a2df9be856e23fcfc6cc66d0d1a35fd from master