test(unit/runner.spec.js): Minor tweeks related to #3686 (#3704)
test(unit/runner.spec.js): Minor tweeks related to #3686 (#3704)

* Refactored portions of tests for increased clarity.
* Updated code to run all stacktrace tests on Windows (previously skipped).
* Updated/replaced logic for generation of overlong messages used in filter tests.
adamgruber/mocha,adamgruber/mocha,outsideris/mocha,mochajs/mocha,outsideris/mocha,mochajs/mocha,adamgruber/mocha,mochajs/mocha