TokenDetectionController: Write comprehensive unit tests

[mcmire]

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.

[MajorLift]

Merging TokenDetectionController with DetectTokensController has introduced new behaviors and branches. These are some new tests that will need to be added:

• Correctly responds to KeyringController:lock, KeyringController:unlock, AccountsController:selectedAccountChange, PreferencesController:stateChange events.
  • Resets polling interval to default value (3 minutes) when responding to these events.
• Correctly responds to the isUnlocked property of keyring-controller being set to false when the controller is initialized.
  • Specifically, passive auto token-detection in response to subscribe events is blocked.
• Correctly pulls the useTokenDetection property using the Preferences:getState action when controller is initialized.
  • Performs token detection on legacy token list if selected network is Mainnet even if token detection is disabled by preferences controller.
• Does not detect tokens that are already in the tokens-controller detectedTokens list.
• trackMetaMetricsEvent is called with the expected options object arguments.

The following are the recommended minimum target coverage thresholds, defined by the threshold values prior to the changes introduced by #3775.

      branches: 88.36,
      functions: 97.08,
      lines: 97.23,
      statements: 97.28,

[desi]

Hey team! Please add your planning poker estimate with Zenhub @Gudahtt @kanthesha @MajorLift @mcmire @mikesposito

[MajorLift]

The scope of this ticket no longer includes the API changes caused by the consolidation with DetectTokensController.

However, it needs to update the tests in the extension detect-tokens.test.js file to align with the current controller API, and integrate these test cases into the core TokenDetectionController.test.ts file. This effort will include removing redundant or obsolete tests.

[MajorLift]

• https://github.com/MetaMask/core/issues/3661 is fixed by https://github.com/MetaMask/core/pull/3938 (https://github.com/MetaMask/core/pull/3938/commits/f060ced256d24ce5069873e44686cd5d152960d0), but no unit tests were written for this behavior change.
• We should write these tests in this ticket.