#33348: Change API of assertFormError to take an actual form object
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               Reporter:  Baptiste Mispelon     |          Owner:  nobody
                   Type:  Cleanup/optimization  |         Status:  assigned
              Component:  Testing framework     |        Version:  dev
               Severity:  Normal                |       Keywords:
           Triage Stage:  Unreviewed            |      Has patch:  0
    Needs documentation:  0                     |    Needs tests:  0
Patch needs improvement:  0                     |  Easy pickings:  0
                  UI/UX:  0                     |
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 The current signature of `assertFormError` is `(response, form, field,
 errors, msg_prefix='')` where:

 - `response` is a response object (specifically one generated by the test
 client because it needs `response.context`)
 - `form` is the name of a form (string) to be found in the response's
 context
 - `field` is a name of a field in the form (string)
 - `errors` is either a list of error strings, a single error string
 (equivalent to `[error]`) or `None` (equivalent to `[]`)
 - `msg_prefix` is a string added to the test failure message


 Personally I've always found this `response`/`form` API to be clunky since
 I often want to test a form directly without having to go through the test
 client.
 It would be a lot easier to use if we could pass a form object directly. I
 don't really understand why the API was implemented like this to begin
 with.

 On top of that, now that Django uses template-based rendering for forms,
 formsets and widgets there are a lot of contexts to search in
 `response.context` and a lot of possibilities for clashing names (see
 #33346).

 I would therefore propose the following new signature:
 `assertFormError(form, field, errors, msg_prefix='')` with `form` being an
 actual `Form` object and all other parameters staying the same.
 The deprecation should be straightforward to implement by checking if
 `form` is a response object (`isinstance` check) or if `response` kwarg
 has been passed.


 With that change `assertFormsetError` becomes mostly useless since one can
 simply do `assertFormError(formset.forms[i], field_name, errors)`. The one
 usecase that wouldn't be covered is `i = None + field_name=None` which
 checks the `errors` list against the formset's `non_form_errors()`.
 We could either leave `assertFormsetError` in place as a convenience
 method (with a similar change to its API to accept a formset object
 directly) or deprecate more agressively by suggesting the user tests the
 output of `formset.non_field_errors()` directly.

-- 
Ticket URL: <https://code.djangoproject.com/ticket/33348>
Django <https://code.djangoproject.com/>
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