Consider reorganizing tests

Since everything is in a monorepo, should we put handwritten tests at the top-level?

Pro: easier to run the tests from the top-level
Con: harder to run the tests for a single package

Review the current monorepo test layout and how tests are run from the top level versus within a single package. Compare the trade-offs described in the issue and document a clear organization decision. Done means the repository has an agreed test structure and the resulting commands or layout are clear.

Written by the indexing model from the issue text.