Test & Live Mode Payment Testing with stripe

General question about testing if anyone knows...

if I put FluentCart into test mode, and do a test monthly subscription product purchase with a test Stripe CC number, what happens if I then switch Fluentcart to Live mode before the next monthly payment on this test monthly subscription is due? Would it still process monthly installments in test mode in Stripe for that existing test subscription whilst new signups would now be live?

Would be good if both can run in tandem so that I can test new purchases of new products while existing products are live.

Hopefully making sense here!