What should I do, I have a central function that is not documentated and no test-cases are written for it. I have no clue what the method should really do, I know that it works in 99.9% of all cases otherwise we had much more bugs. Now there is one Unit-Test that reports an issue. I tracked it down to this method, no one touched the method nor the unit-test.
My logical thinking says that there is one statement missing, but it could also fuck up another part of the code... (This project has a bad testing coverage :'( )

What would you do?

- copy paste the method for this special case (I would hate me so much for breaking DRY)
- inheritance?! (Would make it more complex and then it would be still untested / undocumented)
- YOLO changing oO?! (hope for luck, just joking)

P.s it's an edge case unit test, the client / customer probably wouldn't realised it if it happens