The only thing being isolated in sandbox is the restore() register. As such it's generally and usually a much
better practice to use sinon.stub() when stubbing than to call an explicit new sandbox.
sinon, when imported, creates a default sandbox. That sandbox uses a shared register. That shared register will carry across test suites. Without it you have to manually restore the stubs, which you have to already know exists.
Effectively running sinon.restore() before your test suite resets your environment if you used the default sandbox. If you created a second sandbox with sinon.createSandbox() that sandbox will not be restored and you'll then have to manually test your stubs before stubbing, restore them through a loophole based on knowledge of the wrapped structure, and hope you've gotten them all.
Strangely enough stub() will assign to the default sandbox register but, it will be a lesser stub that does not include spy() functionality. You won't be able to track callCount.
The expected environment is a Typescript one. All tests are run against the Generico class. Currently there are no tests for Singletons but, those should also be expected to preserve their prototype across suites.
npm installnpm run testornode node_modules/.bin/mocha -r ts-node/register src/__tests__/*