CallManager: Unit Testing

[Stebalien]

DefaultCallManager

• [ ] send - this is going to be hard to test outside of integration tests. We likely need to become generic over the engine at some point, but not yet.
• [ ] create_actor/next_actor_address
  • Make sure next_actor_address returns a new address after create_actor.
  • Make sure create_actor correctly assignees the delegated address, sets the code, etc..
  • Make sure create_actor leaves the balance in-place when upgrading an embryo.
  • Make sure it refuses to upgrade anything except an embryo.

We need to should test the other method as well, but we need to start with the ones above.