Unit tests should run on file change only once

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Expected behaviour

When running npm run test-live tests should run only once on file change.

Actual behaviour

When running npm run test-live tests run twice on file change.

It's probably related to this [0]

Actually, watching with webpack is better since the tests will be rerun only once - after webpack rebuilds test_index.js.
Watching with karma means that karma will run tests upon change some_test.js and after webpack rebuilds the test_index.js

[0] codymikol/karma-webpack#23 (comment)