chore: use single class per file when possible on tests/ directory

[samsonasik]

Description

So it can match psr-4 definition. This is detected by my structarmed tool:

https://github.com/boundwize/structarmed

for psr4 preset, this is one of functionality, define layers and rules, then keep them enforced.

I can add structarmed to be part of CI later if needed.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[samsonasik]

Ready for review/merge 👍

[neznaika0]

I agree with your opinion

[samsonasik]

Thank you @MGatner @neznaika0 @paulbalandan for the review, let's merge 👍