The Blackboard test setting to turn on “force completion” only allows a student one entry into a test. That’s different than allowing one “try” — force completion means that a student must complete a test after opening it (in the same browsing session).
Nor is force completion the same as “auto-submit,” which sends the test as-is to the gradebook after the timer runs out. With force completion on, students get kicked out of a test if there’s any connectivity loss or disruption (College of DuPage sums this up well) and can only complete it if the instructor resets the test (by ignoring or deleting that test attempt).
Like prohibit backtracking, this setting won’t “break” Blackboard, but it’s tricky, easy to mess up and we don’t recommend using it.