test: fix invalid test and source map test

[alexander-akait]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

fixes #285

Breaking Changes

No

Additional Info

To disable source maps generation you need set sourceMap: false for css-loader and set devtools: false, we will try to fix and simplify it in webpack@5

[codecov]

Codecov Report

Merging #481 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #481   +/-   ##
=======================================
  Coverage   88.49%   88.49%           
=======================================
  Files           5        5           
  Lines         426      426           
  Branches       94       94           
=======================================
  Hits          377      377           
  Misses         47       47           
  Partials        2        2

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