Determining which tests cover a line of code
Is there a way to determine the set of unit tests that will potentially execute a given line of code? In other words, can you automatically determine not just *whether* a given line is covered, but the actual set of tests that cover it?

Consider a big code base with, say, 50K unit tests. Clearly, it could take a LONG time to run them all--hours, if not days. Working in such a code base, you'd like to be able to execute some **subset** of all the unit tests, including only those that cover the line (or lines) that you just touched. Sure, you could find some manually and run those, but I'm looking for a way to do it faster, and more comprehensively.

If I'm thinking about this correctly, it should be possible. A tool could statically traverse all the code paths leading out of each unit test, and come up with a slice of the program reachable from that test. And you should then (theoretically) be able to compute the set of unit tests that include a given line in their slice, meaning that the line could be executed by that test ("could" rather than "will" because the actual code path will only be determined at run time based on the inputs or other conditions). A given line of code could have a massive number of tests that execute it (say, code in a shared library), whereas other lines might have few (or no) tests covering them.

So:

 1. Is my reasoning sound on this idea? Could it theoretically be done, or is there something I'm leaving out?

 2. Is there already a tool out there that can do this? Or, is this a common thing with a name I haven't run into? Pointers to tools in the java world, or to general research on the subject, would be appreciated.
Determining which tests cover a line of code
===

Is there a way to determine the set of unit tests that will potentially execute a given line of code? In other words, can you automatically determine not just *whether* a given line is covered, but the actual set of tests that cover it?

Consider a big code base with, say, 50K unit tests. Clearly, it could take a LONG time to run them all--hours, if not days. Working in such a code base, you'd like to be able to execute some **subset** of all the unit tests, including only those that cover the line (or lines) that you just touched. Sure, you could find some manually and run those, but I'm looking for a way to do it faster, and more comprehensively.

If I'm thinking about this correctly, it should be possible. A tool could statically traverse all the code paths leading out of each unit test, and come up with a slice of the program reachable from that test. And you should then (theoretically) be able to compute the set of unit tests that include a given line in their slice, meaning that the line could be executed by that test ("could" rather than "will" because the actual code path will only be determined at run time based on the inputs or other conditions). A given line of code could have a massive number of tests that execute it (say, code in a shared library), whereas other lines might have few (or no) tests covering them.

So:

 1. Is my reasoning sound on this idea? Could it theoretically be done, or is there something I'm leaving out?

 2. Is there already a tool out there that can do this? Or, is this a common thing with a name I haven't run into? Pointers to tools in the java world, or to general research on the subject, would be appreciated.