Local development tooling
Similar to AWS SAM (https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-cli-using-invoke.html) or Google Cloud Functions Framework (https://cloud.google.com/functions/docs/functions-framework).
I.e. the ability to run functions locally. It's expensive and slow to have to run and test code in a project remotely all the time even for small changes.
+ 1 for this. Testing and developing functions is a real time killer. We've also found that once you deploy a function, it takes time to propagate so multiple calls to the function are required to see the change.
Not only for functions, but also please consider local tooling for graphql.
AWS Amplify has a local development feature which is really useful. Just run a simple command `amplify mock api` then you get a locally running graphql endpoint. It really speeds up both development and testing.