>> What about these patches?  Should the first patch also test the
>> following case?
>>
>> +                (let ((numbers (generation-numbers profile)))
>> +                  (if (equal? numbers '(0))
>> +                      (exit 1)
>> +                      (for-each list-generation numbers))))

> The first patch below already contains that snippet, so I’m not sure
> what you mean.

There are two cases:

1. A generation does not exist.

2. The profile points to the zeroth generation, and there are no other
   generations.

‘tests/guix-package.sh’ tests the first case.  Should we test the second
case too?  What would be the best way to do so?  Note that you can’t
specify the pattern in that case because of the (string-null? pattern)
bit.