Using Play 2.4 with a renamed `conf/routes` file - playframework-2.4

Question

My simple Play 2.4 project does not compile when I rename the conf/routes file to something else, e.g. conf/hello.routes. The reason I'm doing this is to enable composition of APIs while allowing them to be developed in separate git repositories and sbt projects.
The idea of multiproject support is based on this project and blog post - but that's using Play 2.3.
The error I get is:
$ sbt test
...
[info] Hello should
[error] ! give {hello: true}
[error] Unable to provision, see the following errors:
[error]
[error] 1) Error in custom provider, java.lang.ClassCastException: interface play.api.routing.Router is not assignable from class hello.routes
[error] while locating play.api.test.FakeRouterProvider
[error] while locating play.api.routing.Router
[error]
[error] 1 error (InjectorImpl.java:1025)
[error] com.google.inject.internal.InjectorImpl$2.get(InjectorImpl.java:1025)
[error] com.google.inject.internal.InjectorImpl.getInstance(InjectorImpl.java:1051)
[error] play.api.inject.guice.GuiceInjector.instanceOf(GuiceInjectorBuilder.scala:321)
[error] play.api.inject.guice.GuiceInjector.instanceOf(GuiceInjectorBuilder.scala:316)
...

Answer 1

Got this resolved (code in the git repo now works).
The problems were likely connected to both of these:
the Controller implementation wants to be within a package controllers.hello instead of just hello
in the application.conf file one should omit the controllers namespace, i.e.
play.http.router = app.Routes
I learned this simply by comparing this code with samples that work.