Add spec for users behavior

[etagwerker]

@benphelps introduced new users behavior in #9. We should add a spec to cover this new behavior.

[krishna543019]

Hi,
Are you adding invoices, invoice_line_items soon ? That would be much helpful to this great gem

Thanks

[etagwerker]

@krishna543019 I don't have any plans to do that soon. If anyone is interested in doing that, we welcome pull requests with open arms 😄 -- someone made some progress over here: https://github.com/ombulabs/harvesting/pull/35/files -- feel free to continue their work 👍

[etagwerker]

I see that there is now a spec for client#users. So I'm closing this issue.