Eli Zaretskii <eliz@gnu.org> writes:

>> From: Daniel Martín <mardani29@yahoo.es>
>> Date: Sun, 03 Jan 2021 18:16:46 +0100
>> 
>>  (ert-deftest xref--xref-file-name-display-is-abs ()
>> -  (let ((xref-file-name-display 'abs))
>> -    (should (equal (delete-dups
>> -                    (mapcar 'xref-location-group
>> -                            (xref-tests--locations-in-data-dir "\\(bar\\|foo\\)")))
>> -                   (list
>> -                    (concat xref-tests--data-dir "file1.txt")
>> -                    (concat xref-tests--data-dir "file2.txt"))))))
>> +  (let ((xref-file-name-display 'abs)
>> +        ;; BSD find may add an extra '/' to the path.
>> +        (expected (list
>> +                   (concat xref-tests--data-dir "/?file1.txt")
>> +                   (concat xref-tests--data-dir "/?file2.txt")))
>
> Why are we producing file names by concatenation, instead of calling
> expand-file-name?  Wouldn't using the latter solve the problem?  Or
> what did I miss?

Yes.  I've attached another solution in terms of expand-file-name and
file-relative-name.