Test suite hangs when [[Resolve]](promise, x) steps 2.2 / 2.3 are skipped

[biril]

Skipping steps 2.2 / 2.3 of [[Resolve]](promise, x) and using 2.1 as a 'generalisation', goes unnoticed by the test suite (all tests pass). However it causes it to hang, i.e. it'll run all tests, they will all pass, but it just won't exit afterwards. (A quick look reveals that this is due to process.nextTick nextTick-ing forever but I haven't clearly isolated the sequence of events that leads to this.)

This seems to hint at some shortcoming of the suite itself but in any case it should be further investigated.