Reverse Coverage: Find which tests execute which lines of code

Occasionally it could be useful to discover how is tested/executed/documented (in the way of tests as Living Documentation) a line (or set of lines) of an application.For example, when you create a part that stands over a product (like a Rails Engine), you override methods, alter classes at runtime, add new behaviors that could bring regressions to the underlying system. So it can help to check what/how specs treat the original lines of code.