We should add a Javascript test that exercises a rollback scenario where the sync source is receiving operations while the rollback is under way. This can be made more deterministic by utilizing the fail points described in SERVER-31370. There may be a few interesting cases to test here. For example, a collection that gets dropped or renamed mid-way through the document refetching process. Or a document that gets deleted mid way through the refetching process. The main goal is to at least provide a basic test for this scenario since there are no existing tests that explicitly test this currently.