Unit Tests fail shortly after Karma starts

[BrianPiere]

Kibana version:
7.3.2

Elasticsearch version:
7.3.2 (running es snapshot)

Server OS version:
Windows 10 Pro: 1809

Browser version:
Chrome: 77.0.3865.90

Original install method (e.g. download page, yum, from source, etc.):
git clone from Github

Describe the bug:
The unit tests begin to run and Karma starts at http://0.0.0.0:9876/. The browser window opens and says it's connected, then closes and an error occurs in the console.

Steps to reproduce:

1. yarn test:browser from command line

Provide logs and/or server output (if relevant):

Running "karma:unit" (karma) task
01 10 2019 17:47:11.379:INFO [karma-server]: Karma v3.1.4 server started at http://0.0.0.0:9876/
01 10 2019 17:47:11.383:INFO [launcher]: Launching browsers Chrome with concurrency unlimited
01 10 2019 17:47:11.389:INFO [launcher]: Starting browser Chrome
01 10 2019 17:47:12.253:INFO [Chrome 77.0.3865 (Windows 10.0.0)]: Connected on socket MiXTHZCqHYy7xk5WAAAA with id 22684979
Chrome 77.0.3865 (Windows 10.0.0) LOG: 'ready to load tests for shard 1 of 1'

Chrome 77.0.3865 (Windows 10.0.0) ERROR: TypeError: Cannot set property 'type' of undefined
TypeError: Cannot set property 'type' of undefined
    at http://localhost:5610/bundles/tests.bundle.js:77465:14
    at Array.forEach (<anonymous>)
    at http://localhost:5610/bundles/tests.bundle.js:77464:14
    at Array.forEach (<anonymous>)
    at Object../src/legacy/ui/public/agg_types/index.js (http://localhost:5610/bundles/tests.bundle.js:77463:19)
    at __webpack_require__ (http://localhost:5610/bundles/tests.bundle.js:21:30)
    at Object../src/legacy/ui/public/vis/editors/default/components/default_editor_agg_params.tsx (http://localhost:5610/bundles/tests.bundle.js:121468:18)
    at __webpack_require__ (http://localhost:5610/bundles/tests.bundle.js:21:30)
    at Object../src/legacy/ui/public/vis/editors/default/index.ts (http://localhost:5610/bundles/tests.bundle.js:123091:34)
    at __webpack_require__ (http://localhost:5610/bundles/tests.bundle.js:21:30)

Any additional context:
I'm developing a Kibana plugin in beginning stages. Everything works fine running it within Kibana dev mode.

[elasticmachine]

Pinging @elastic/kibana-operations (Team:Operations)

[tylersmalley]

@BrianPiere, apologies as this issue fell through the cracks. Is this still a problem you're facing? We have continued running these tests without reproducing this issue.

[jbudz]

We can close this out for now, karma testing has been removed with #73126