#29308: Clarify how assertQuerysetEqual()'s transform parameter works
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Reporter: Alexander Todorov | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: Documentation | Version: 2.0
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by Tim Graham):
* type: Bug => Cleanup/optimization
* stage: Unreviewed => Accepted
* component: Testing framework => Documentation
Old description:
> 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.
New description:
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.
--
Comment:
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()`.
--
Ticket URL: <https://code.djangoproject.com/ticket/29308#comment:1>
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