Many programmers would prefer to mock in their client library specs, but doing so could result in the service and client passing all specs with hidden failures.

You create a file called user.rb in the /models directory:

for the service in spec/service_spec.rb, you add another describe block:

For invalid user name and password combinations, the service should return a 400 HTTP status code, which means that the server received a “bad request.” The service could also use the 401 (“unauthorized”) response code, but that code specifies that authentication credentials need to be in the request header, which is not quite what is required.

However, for the purposes of migrating existing Rails applications to services, the shared database approach may be necessary in the early stages.

Services isolated on business logic can share data sources with other systems.