Saving plan charged much more than I expected and suddenly applied to current test env

Can you share more details of your Saving Plan? What is the upfront? You pay what you agreed the terms to be. It applies right away and doesn't matter you change your usage or not. It is a commitment to pay an amount of dollar in an hourly rate throughout the SP term as a discount price for a on-demand usage equal to an amount estimated at the time of purchase.

Are you separating your prod and dev environments in a multi-account strategy? Do you AWS organization where you purchase the Saving Plan in the payer account? If yes to both, visit this page in your AWS account to deactivate any account you don't want to Saving Plan and RIs to be applied to : https://us-east-1.console.aws.amazon.com/billing/home?region=us-east-1#/preferences

If you are having dev computer and prod compute in the same account, there isn't a way to control how the Saving Plan rates are applied to which usage! The only separation you can have control to is the account level, and not the resource level. Consider separating the environments in different AWS accounts. Then deactivate sharing SP with dev account in the management account. Additional knowledge shared here: https://repost.aws/knowledge-center/savings-plans-consolidated-billing https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/ri-turn-off.html