How to integrate karma in webpack

I am a webpack newbie and have a question about testing.

I have a project which uses webpack, typescript and karma as test runner and I would like to run my tests on every file change (e.g. in "watch" mode)

I am aware of karma-webpack and it works well when I run karma as own process (karma start ...)

But what I want is to integrate karma in the webpack flow. So, from my naive point of view, I thought karma has to be defined in preloading of webpack (such as a linter).

But I found nothing.... I can not believe that this common workflow is not possible (run tests on every source change)

Can anybody of you give me a suggestion?