Is there a difference between running a FULL and running a SELECTIVE?
Example: You want to test a backup so you click on a 1-Time backup option, click Include, choose a file to backup, and submit this job.
Yes, and it is VERY important that you select the correct one so that your current and future backup chains are not adversely affected by your choice of backup strategy type.
SELECTIVE: A stand-alone backup that is not affiliated or merged into any backups in the current or future backup chain set.
FULL: The completed job seals the previous backup set and starts a new backup chain set, with the newly created Full backup as the footprint for all new backups to follow. This new Full (Master) is a Parent, and all Incremental "Child" backups are related to it. If you are using an Incremental Forever strategy, it uses the Full and the Child Incremental backups to generate a new "Synthetic Full" as the new Parent backup.
SHORT ANSWER: Always use Selective option to create a backup test. Never use the Full option with an Include or exclude option unless it is the exact same options for the normal schedule. The new Full is referenced by future Differentials/Incrementals