Adding integration tests for shore diff

[dkirillov]

Summary

shore diff was the latest command to be added to Shore and is lacking integration tests that other commands have.

Integration tests should be added for it.

Motivation

To ensure that the command is working as intended. There's already been a case (#76) that had the command broken.

Describe alternatives you've considered

None.

Additional context

Added for tracking purpose based on comment here - #77 (review) .