How to properly add unit tests to a project?

Question

JavaScript

Hey!
I can't figure out how to properly organize module testing for a web application. I am doing this for the first time and I can not decide on the structure that will be correct.
Abstraction of my project structure:

app
-index.js
----graphql
       |--schema.js
       |--mutation.js
       |--query.js
----pages
       |--main.js
       |--other.js
----public
       |--another.js

Now I do it this way:

app
-index.js
-index.test.js - сюда буду реквайрить остальные .test. файлы
----graphql
       |--schema.js
       |--mutation.js
       |--query.js
       |--schema.test.js
       |--mutation.test.js
       |--query.test.js
----pages
       |--main.js
       |--other.js
       |--main.test.js
       |--other.test.js
----public
       |--another.js
       |--another.test.js

Those. I just copy each separate file in which I will do tests for functions. I do this so that extra code does not get into production.
But I doubt very much that this approach is correct.
In the future, I will build the project in production as a webpack, where all files with the .test..
Question:
How to properly add unit tests to a project?