TokenDetectionController: Write comprehensive unit tests

We should review the tests for TokenDetectionController and ensure that the functionality and edge cases are well-covered by tests and that there are no duplicative or unnecessary tests. A new contributor should be able to use the tests as a guideline for what the controller does.

~There were API changes made recently to TokenDetectionController, so we should focus on backfilling tests for those especially.~ This is no longer the case, but see comments below for updates.

Start by locating TokenDetectionController and its existing tests in the monorepo, then read the controller and run its current unit-test suite. Use the existing tests to identify uncovered functionality and edge cases, remove duplicative or unnecessary cases, and consider the work done when the tests clearly describe the controller's behavior and pass.

Written by the indexing model from the issue text.