Add unit tests to the tag commands

[Zabuzard]

We recently merged command unit testing utilities.

That being done, we should now add unit tests for the tag system (tags, tag, tag-manage) to increase our test coverage.

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.

[Zabuzard]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.

Since the tag system is really critical to our daily life, this is relevant and should be done eventually.

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.