What happened to the --exec flag and what's the workaround for integration tests?

I had an old project that worked on `v3.20.3`, we were starting up the offline server and then running integration tests against it, e.g.

`serverless offline start -stage=mock --exec \"npm run integration\"`

In later versions it seems like this flag has been removed from serverless-offline. So what's the workaround to run integration tests?