[WIP] run each test via fork/exec
split loading and running of tests
implemented multi process runner
run all test methods at once
automatically filter test files from coverage
make coverage optional when loading test files
detect test errors and unlock coverage if necessary
respawn failed tests
refactored ProcClazz; also delete stale data on failure
refactor
refactor
fixed coverage bugs with ForkingClass (respawn tests)
refactored ProcClazz to use ForkWorker
combined Proc & Forking impls with common base class
cleanup
always checkpoint during teardown
refactor: re-use ForkWorker in Runner