Finish path module
In the automations path used for displaying forms, you can add the Finish path module and connect it to the "submit" exit node.
The information will then be visible in the Automation section in the "Finished" column.
Bear in mind that if you're testing two or more forms, this method won't be appropriate as data from all of the forms will be aggregated and stored as one. You won't be able to know how many submissions each form garnered individually.
Tags and attributes
This solution is more flexible, but its results won't be visible at first glance.
The idea is to add a proper tag or to update the value of a given custom attribute.
Then, when people fill out your forms, you will simply need to go to the People section and filter users by the appropriate tags/attribute values and compare the results.