--prioritize TEST1,TEST2,...
                 select these tests first, even if the order is randomized.

--prioritize is used to influence the order of selected tests, such that
the tests listed as an argument are executed first. This is especially
useful when combined with -j and -r to pin the longest-running tests
to start at the beginning of a test run. Pass --prioritize=test_a,test_b
to make test_a run first, followed by test_b, and then the other tests.
If test_a wasn't selected for execution by regular means, --prioritize will
not make it execute.