refactor: :recycle: divide tests into app and core folders

[signekb]

Description

These changes are done so the test folder structure mimics the sprout structure more. This should help us keep an overview of the tests.

Note that with the refactoring work we'll do in this iteration, most of the tests will have to be reworked, so this is just an initial step to improve the structure a bit.

I also fixed one test in MetadataStepConfirmationTests that had a typo: assertEquals -> assertEqual

Closes #515

Reviewer Focus

This PR needs a quick/in-depth review. Focus on CHANGES.

Checklist

• [X] Added or updated tests
• [X] Tests passed locally
• [ ] Linted and formatted code
• [ ] Build passed locally
• [ ] Updated documentation