My company has some plastic enclosures with circuit boards inside. The board has been exposed to corrosion, which we will repair and test for continuity and current. Is there a test that can test for "longevity" or durability of the trace? For example, we repair a trace, tests good for continuity/current, how long with the trace last (is the test we need).
As has been stated in comments, the answer is a deafening no!.
Corrosion on pcbs can be caused by any number of things, and leftover flux from your repair process is a real danger. Otherwise, corrosion rates will depend on environmental conditions, and you have no good way to model these.
Worse, your repair process seems to be aimed at repairing corrosion damage which has actually caused a failure. If one part is being corroded, the odds are that others have been affected as well, and are just waiting to go south. These hidden failure points can be in any state of damage.
Since the products your company works on have (by definition) suffered corrsion damage, it is clear that they will continue to suffer damage, and so you need to take measures to prevent this above and beyond what the original product produced. Tony Stewart is correct in recommending conformal coat, not to mention testing. This might be overkill for "regular" products, but the nature of your problem indicates that more stringent measures are appropriate.