the conversion was relatively simple MDL-32323 , I have created some emulation for old style $this->assert() in engine/tests/helpers.php

I have found two issues:
1/ type/match/tests/walkthrough_test.php - tests are failing randomly, looks like some weird randomisation is going on there - see TODOs
2/ type/multianswer/tests/upgradelibnewqe_test.php contains invalid expected value - see TODO