Context
HomeDBManager lacks of direct tests, which makes hard to make rework or refactorations.
Proposed solution
Specifically here, I introduce tests which call exposed UsersManager methods directly and check their result.
Also:
I removed updateUserName which seems to me useless (updateUser does the same work)
Taking a look at the getUserByLogin methods, it appears that Typescirpt infers it returns a Promise<User|null> while in no case it may resolve a nullish value, therefore I have forced to return a Promise<User> and have changed the call sites to reflect the change.
Related issues
I make this change for then working on #870
