MCVE to demonstrate that a Karma runs specs twice

This MCVE shall demonstrates the minimal config to demonstrate how running Karma via the API loads and executes tests twice.

Symptom

The tests run twice. Even the .spec file is loaded twice.

...
HeadlessChrome 72.0.3626 (Linux 0.0.0) INFO: '### SCRIPT LOADED'
HeadlessChrome 72.0.3626 (Linux 0.0.0) INFO: '### SCRIPT LOADED'
17 03 2019 22:13:46.477:DEBUG [HeadlessChrome 72.0.3626 (Linux 0.0.0)]: CONNECTED -> EXECUTING
..17 03 2019 22:13:46.505:DEBUG [HeadlessChrome 72.0.3626 (Linux 0.0.0)]: EXECUTING -> CONNECTED

HeadlessChrome 72.0.3626 (Linux 0.0.0): Executed 1 of 1 SUCCESS (0.029 secs / 0.004 secs)

HeadlessChrome 72.0.3626 (Linux 0.0.0): Executed 1 of 1 SUCCESS (0.029 secs / 0.004 secs)

When running Karma via its CLI ...

$ node_modules/bin/karma start

... the issue does not occure:

...
HeadlessChrome 72.0.3626 (Linux 0.0.0) INFO: '### SCRIPT LOADED'
17 03 2019 22:20:37.400:DEBUG [HeadlessChrome 72.0.3626 (Linux 0.0.0)]: CONNECTED -> EXECUTING
.17 03 2019 22:20:37.406:DEBUG [HeadlessChrome 72.0.3626 (Linux 0.0.0)]: EXECUTING -> CONNECTED

HeadlessChrome 72.0.3626 (Linux 0.0.0): Executed 1 of 1 SUCCESS (0.006 secs / 0.004 secs)

Install depencencies (once)

$ npm install

Run the demo

$ node mcve.js