Failing test: Browser Unit Tests."before each" hook."before each" hook

[spalger]

Failure: https://kibana-ci.elastic.co/job/elastic+kibana+master/JOB=kibana-intake,node=immutable/520/testReport/junit/Browser%20Unit%20Tests/%22before%20each%22%20hook/_before_each__hook/

We've been seeing a couple flaky failures in the before each hook setup in the Karma tests. It's unfortunately cryptic, and not super flaky, but it started showing up in #37311 and has happened a number of times on master/7.x/other PRs since #34532 was merged.

Stacktrace:

Error: Uncaught TypeError: Cannot set property 'filters' of undefined (webpack://%5Bname%5D/./node_modules/rxjs/internal/util/hostReportError.js?:4)

I'm not totally clear what's happening here, but it seems that a subscriber somewhere is trying to do something that triggers an exception. We might be able to overwrite this module in rxjs to produce better error reporting, but it wouldn't surprise me if that doesn't actually work and the error getting through is basically as meaningless as Cannot set property 'filters' of undefined...

[elasticmachine]

Pinging @elastic/kibana-app

Sorry kibana app team for the extra ping!

[elasticmachine]

Pinging @elastic/kibana-test-triage

[elasticmachine]

Pinging @elastic/kibana-app-arch