Adding integration tests for shore diff

## 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 - https://github.com/Autodesk/shore/pull/77#pullrequestreview-1422608493 .

Start by examining the existing integration tests for Shore's other commands and the implementation of `shore diff`; review issue #76 for the reported breakage and pull request #77 for context. Add equivalent integration coverage for `shore diff` and confirm the tests pass and catch the failure described in #76.

Written by the indexing model from the issue text.