Depending on what the flow and smart list are:
Smart List: just add Email Address= or CONTAINS you@yourcompany.com or @testdomain.com. I always keep a list of test leads and use those. I call this "putting on the brakes"
Flow: if you have wait steps, always modify these to 1 minute.
If you have multiple possibilities or actions, you will need to take those actions, one at a time, monitor the results, and then reset the leads to go again.
Schedule: run every time because you will re-use leads.