myProject
 └ build.sbt
 └ app - this code works perfect
 └ modules
   └ testModule
     └ build.sbt
     └ src
       └ main
         └ scala - here I have simple object Foo with method which returns string
       └ test
         └ scala - here is Spec2 test for Foo object with JUnitRunner
 └ test - here is Spec2 tests for app and these tests also works fine

scalaSource in Test <<= baseDirectory / "src" / "test" / "scala"