Move test files so that file structure matches constant nesting structure

[alexevanczuk]

What are you trying to accomplish?

Follow-up to #276 (comment)

In this PR, we're moving test files into folder structures that matches their naming convention. Although we are not using zeitwerk to load test files, we thought this is a best practice that improves navigatability of the codebase.

What approach did you choose and why?

I chose test/* as a sort of "autoload" path in zeitwerk parlance, with anything that follows that to constitute a portion of the constant namespacing.

That is, test/support and test/integration are organizational units to organize test files into general buckets. Everything that follows represents a portion of the namespace.

What should reviewers focus on?

Does the nesting make sense?
Should we enforce this by actually loading test constants with zeitwerk?

Type of Change

• Bugfix
• New feature
• Non-breaking change (a change that doesn't alter functionality - i.e., code refactor, configs, etc.)

Checklist

• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• It is safe to rollback this change.

[gmcgibbon]

Thanks!