bug#34070: 27.0.50; icomplete-mode candidate cycling broken for C-x C-f

[João Távora]

Eli Zaretskii <eliz@gnu.org> writes:

>> Seems to have been introduced by
>> 
>>    commit 65797b1d75e9f608ffd50fd88be47a854b143bb1
>>    Author: Drew Adams <drew.adams@oracle.com>
>>    Date:   Thu Apr 28 19:31:43 2016 +0200
>>     
>>        Make icomplete respect `completion-ignored-extensions'
>>        
>>        * lisp/icomplete.el (icomplete-completions): Heed
>>        `completion-ignored-extensions' (bug#12939).
>> 
>> Naive patch attached that seems to fix it for me.
>
> Please add a test for this, if possible, so that we don't screw this
> up again in the future.

I'd love to, but it's not exactly simple to write tests that observe
user interaction the minibuffer with ert.  At least for me.  How would I
go about doing that?  Any pointers/prior art?

João