error: RequestRejected(no other error details). What are usual reasons for this error pls?

 I am developing a rest service in akka http for the first time. Even though there exists a matching path/route for the HTTP Verb in the ABCRoutes.scala, the corresponding unit test fails with an error: RequestRejected(no other error details). What are usual reasons for this error pls? Thanks much
are there any akka http specific scalac options I can add in build.sbt , to make the above error more verbose pls?