sbt directory structure
src/
main/
resources/
<files to include in main jar here>
scala/
<main Scala sources>
scala-2.12/
<main Scala 2.12 specific sources>
java/
<main Java sources>
test/
resources
<files to include in test jar here>
scala/
<test Scala sources>
scala-2.12/
<test Scala 2.12 specific sources>
java/
<test Java sources>