[TIP] A tool to guess what tests to run given a diff?

[Kumar McMillan]

My search-foo is failing but I thought there was a post on TIP or
mention somewhere in the community about a tool that can be used to
guess what tests to run based on a diff.  Does this ring a bell?  For
a very large test suite I'd like to take my current diff that affects
unknown parts of the system and figure out which tests I should run.
This obviously would never be 100% accurate but it might serve as a
quick spot check before pushing to a continuous integration server
that will run the whole entire suite.  Slow tests are not fun.

I guess this would work in reverse to code coverage: you'd take a
function or module and ask which tests execute that code.  Python's
trace will probably support this but it would be nice if someone has
already done the work to set it up.

-Kumar