This tool doesn't run all the tests, only the ones affected by the code changes since the last run. It figures out which tests to run by initially running all tests, and storing the code coverage of each test.
It doesn't need to rely on "test change likelihood" - if a code change is outside of the code coverage of the test, it doesn't affect the test.
It doesn't need to rely on "test change likelihood" - if a code change is outside of the code coverage of the test, it doesn't affect the test.