How do we test Sending reminder emails?

Lately i tried this tutorial to activate redmine email reminder if some issue(s)'s duedate is coming with this syntax :

rake redmine:send_reminders days=7 RAILS_ENV="production"

but i don't know if it is activated or not, can you help me where to see if this syntax is activated or not?

and how do we test the sending reminder emails?

thanks, best regards

Redmine