How to make `sbt test` to run tests in main project and all subprojects (or some selected set)

I have a main project and a few subprojects. When I want to run tests, currently I have to do sbt test and sbt subProjectName/test. Is there any way of making sbt run all tests or for example all tests in the main project and one of the subprojects.

I am using Build.scala configurations, but can't find a way of setting this.

Thanks!