The ECSPodCreator will have to create ECSPod objects, which are basically just groups of containers backed by ECS tasks. It should call the methods necessary to register the task definition and run the task, then create the ECSPod object based on those inputs. If it uses secrets, then it will have to create those secrets as well using the Vault before it can start running.
Testing this will require some ECSClient and Vault methods to be implemented first. In particular, we'll need to implement at least (ECSClient).StopTask, (EcsClient).DeregisterTaskDefinition, and (Vault).DeleteSecret so that we can clean up the resources created in the underlying AWS infrastructure once the test has finished running.