In the context of quick tests I’m not sure having to use docker save to create tarballs before each execution of bundle is much better than just performing a docker push to a registry.
Furthermore, it’d be better practice to check your container images into a registry rather than just keeping local copies and tarballs. That way you have an iterative record of your container images, similar to checking code in with git.
I must ask, is there a reason you can’t use a registry? It doesn’t need to even be Dockerhub, you can easily host a small local registry on your development machine.
Best Regards,
Jeremias