Post mortem: checks with async IIFE reporting success incorrectly

Between June 5th, 2020 and June 12th, 2020, checks using async IIFE syntax were incorrectly marked as passed due to changes in security measures for Browser checks. The issue affected 18 active checks and was caused by a change that altered the way promises are handled in the runner. After a customer reported an outage not detected by their tests, the issue was identified and resolved quickly with a fix implemented just hours after it was reported. The fix ensured that the node process exits after executing all promises, rather than exiting immediately when the execution block finishes.