In Drupal I've scheduled, on the future, some e-mail, using rules schedule module. Now I want to force the delivery, before the scheduled time, to check the text of e-mail. Is this is possible?
Yes, you can do it by clicking the execute link in your components tab.
OR, you can click the schedule link and schedule something to run 1 min from now. Just remember that your scheduled action will only run after cron runs. So if you have set cron to run once a day or every 1 hour, it won't happen until then. So will have to manually run cron, by clicking the run cron button to see if it gets delivered after 1 min from now.
There is no out-of-the-box solution to force the execution of an already scheduled rule before the "scheduled date". All you can do for such scheduled rules is to "delete" such rules from the list of schedule rules (via
admin/config/workflow/rules/schedule), so that they don't actually get executed.
There are indeed the "operations" like execute and schedule, as already mentioned in the previous answer, but using those options you actually trigger a new instance of such rule to be executed (they do not actually release an already scheduled rule).
They only way around this, and to do something similar to what you're asking for, is to temporary adapt (or clone) the rule you already have in place, and schedule the rule to be executed after (eg) a few minutes already. But in this case also, you're not triggering the execution of an already scheduled rule: you're only scheduling another rule after (eg) just a few seconds or minutes after such schedule rule gets scheduled.