How can I force the execution of a rule?
Once rules import are set, they are usually automatically launched by cron tasks at the server level, but you can also run them manually with command:
php app/console akeneo:rule:run
You can execute a single rule by adding the code of the rule when using a command
php app/console akeneo:rule:run rule_code
Each time a rule is executed, some new information is added to the application log
2015-08-10 09:27:36] app.INFO: Rule "set_tshirt_style", event "pim_rule_engine.rule.post_apply": 24 items updated.  
Please note that rules are available only on the Enterprise Edition version.