Thinking about using code coverage to speed up a test suite. Run the whole suite once to find which tests cover which code. Then a code change can be tested incrementally by only re-running those tests that cover that code.

Anyone know of a test system that does that?

A difficulty would be when code changes change the coverage (eg, during refactoring). The incremental test run would run too many or too few test cases due to its coverage data being out of date.