Large number of unhandled Promise rejections on

When I run a QUnit test suite on certain packages, if being served by `testee --server`, I get the following error a few seconds after the suite finishes:

`testee.min.js:500 Unhandled promise rejection Error: Timeout of 5000ms exceeded calling api/suites::patch`

The problem is I get this error an unbounded number of times, as fast as the script engine will allow, and it pegs CPU on the page and the dev tools.

This may have something to do with how fast the test suite finishes: I see it happening on very short tests like `can-set` and `can-dom-events`, but large suites like `can-stache` and `can-stache-bindings` don't seem to have this problem.

Start by reproducing a short QUnit suite such as can-set or can-dom-events with testee --server, then inspect the repeated timeout from testee.min.js around the api/suites::patch call. Done means the suite finishes without an unbounded stream of unhandled promise rejections or pegged CPU; compare with larger suites such as can-stache and can-stache-bindings.

Written by the indexing model from the issue text.