Summary:
Cleans up `ScrollView-test.js` to be easier to read and to include a unit test for `ref`.
This prepares the Jest test suite to be extended with an additional test to validate a bug with `ref` invalidation.
Changelog:
[Internal]
Reviewed By: sammy-SC
Differential Revision: D41208894
fbshipit-source-id: 6d79adf131602292f7aa3180b1c230643e9baf16