Flag most recent record in many to many details table

I would suggest adding a 4th table.  Called something like "Renewals"

They would be a child record to the "Employee Tests"

So then any time you have a re-test/renewal. You would click to add a renewal to the test.

This gives you the history, and an easy way to keep track of that particular test, for that particular employee.

If you play the cards right you can have the new record be added in a pop-up window and then when saved it refreshed the record so you have the most recent updates visible.