Why does the project need both Karma and Grunt?

Question

Grunt.js

There is a JavaScript library.
I was given the task to cover it with tests.
And they said to use Grunt and Karma for this.
I have read the docs. It turns out that Grunt is a type of build system to run different tasks and scripts; and Karma is a test runner system.
That is, both Grunt and Karma are "launchers".
Can anyone explain to me what is the point of using both Grunt and Karma at once?
PS I have already been told that Gulp is already being used instead of Grunt, but this does not change the essence - why are BOTH systems needed?

Answer 1

Karma can only launch the browser and feed it a special page. And that's it, even the tests themselves must be written using other libraries. To be honest, I've been in JS for 12 years, but I still don't understand why Karma is needed.
grunt/gulp are general purpose task runners used to organize all processes. Let's say there is a requirement to run the code through linter and unit tests before building, and only then build it. Karma will not help you with this.