That's because that is not the objective of testing (at least outside Waterfall). Tests shouldn't be about testing components, rather behaviors.

I have lots of articles about that, but my latest comment is this one:

- https://drpicox.medium.com/hi-i-believe-that-we-are-really-not-on-the-same-page-b77c868de711

Also I wrote this piece some time ago:

- https://medium.com/codex/the-test-definition-that-destroy-teams-fbdbc05c54bf