Create two categories "Source Category", and "Destination Category".
Create Three posts, one for each category, and the third for both categories.
Run the command to move posts from the "Source Category" to the "Destination Category": wp newspack-content-migrator move-content-from-one-category-to-another --source-term-id=123 --destination-term-id=456
Notice the SQL error and that the posts were not moved.
Switch to this branch and re-run the command.
Notice The Source Category with no posts, and all the posts were moved to the Destination Category.
How to test
wp newspack-content-migrator move-content-from-one-category-to-another --source-term-id=123 --destination-term-id=456Play a bit more with it 😅