The test would previously error out like this:
> synapse_homeserver[1155]: synapse.config._base.ConfigError: You have
> enabled open registration without any verification. This is a known
> vector for spam and abuse. If you would like to allow public
> registration, please consider adding email, captcha, or token-based
> verification. Otherwise this check can be removed by setting the
> `enable_registration_without_verification` config option to `true`.
