Test Pull Policy

[mfleader]

Please describe what you would like to see in this project

The Pull Policy is difficult to test because it is a command with an outgoing message and a hard to observe side-effect. Ideally, this feature would be tested and more robust to changes in how the python deployer interacts with the file system. One solution to this problem is to use a mock that can observe messages about the Pull Policy internal to the python deployer.

Please describe your use case

Please explain how you would use this feature.