Documentation for assertFormError and assertFormsetError doesn't explain all arguments

[Baptiste Mispelon]

The reference documentation for assertFormError [1] and assertFormsetError [2] lists response as a required first argument but doesn't explain what it is.

In contrast, assertContains (the next method on the page) is more explicit:

Asserts that a Response instance produced the given status_code [...]

(though it would have been nice if Response was a link to the relevant doc)

[1] ​https://docs.djangoproject.com/en/dev/topics/testing/tools/#django.test.SimpleTestCase.assertFormError
[2] ​https://docs.djangoproject.com/en/dev/topics/testing/tools/#django.test.SimpleTestCase.assertFormsetError

[Carlton Gibson]

OK, yes, thanks.

[Baptiste Mispelon]

I might have been too quick to mark this as an "easy picking"...

After digging a little, I found that the situation is a bit messier than I'd seen at first. Several custom assert... methods take a response object as a required argument, but some of them will accept any HttpReponse (and subclasses) whereas some require a response object from the test client:

assert	Type of response	attribute
​assertFormError	Test client	response.context
​assertFormsetError	Test client	response.context
​assertContains	Any
​assertNotContains	Any
​assertTemplateUsed	Test client	response.templates
​assertTemplateNotUsed	Test client	response.templates
​assertRedirects	Any

On top of that, while assertTemplateUsed (and assertTemplateNotUsed) does specific error checking to alert the user if they're not using a test client response, assertFormError (and assertFormsetError) do not and simply trigger an AttributeError if you're passing them the wrong kind of response.

I'll get started on a proposed fix for all these issue.

[Baptiste Mispelon]

Here's the PR, split into 3 commits:

1) The documentation changes described in the original ticket
2) Missing tests for assertFormError and assertFormsetError (the failure cases were not tested at all)
3) A small API change to make assertFormError and assertFormsetError raise a ValueError with a helpful message (instead of an AttributeError) when used with a non test-client response (same behavior as assertTemplateUsed).

​https://github.com/django/django/pull/15106

[Mariusz Felisiak <felisiak.mariusz@…>]

In 528691d:

Fixed #33301 -- Clarified the type of arguments required by custom assertions.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 9ac92b1:

Refs #33301 -- Made SimpleTestCase.assertFormError()/assertFormsetErrors() raise ValueError for non test client responses.

[Mariusz Felisiak <felisiak.mariusz@…>]

In aa0c8ff9:

[4.0.x] Fixed #33301 -- Clarified the type of arguments required by custom assertions.

Backport of 528691d1b66b4ecf7bbb55f783fc919d40d4a235 from main