On the form edit page go to Addons → Payments → Stripe, and check the option 'Enable Test Mode'

Test Mode allows use to use a test credit card on our form to check the workflow.

On our form we can now use a test card:

Number: 4242 4242 4242 4242
Expiry: 05/23
CVC: 290

Testing Stripe payment forms
Testing Stripe payment forms

You can find more test card numbers here.

On your Stripe dashboard you can view test payment data by toggle the Viewing test data option on the left-hand menu.

When you are ready to go live with your form simply uncheck the Enable Test Mode option.