I know this question is very vague but I think with your help we can improve it. A couple of month ago in an interview talking about TDD and unit testing, I was asked if I knew I particular methodology (unfortunately I forgot the name) where a class or component gets probed for its correctness by removing or altering some lines (automatically, probably using a specific tool). As you can imagine I didn't get the job and I can't ask the question directly to them but it seems an interesting topic and it also seems they are using it. Anybody has heard about it?
It is called Mutation Testing.
You could take a look at pitest 'Real world mutation testing'