Share Scala class in test folder with Java tests in Maven

I have a Maven project with mixed Java and Scala code. I want to use an auxiliary class located in the scala test folder for Java tests. The file tree is like below, omitting packages:

+ test/
  + java/...
    - SomeTest.java
  + scala/...
    - Aux.scala
    - OtherTest.scala

I want to import code from Aux.scala for use in the SomeTest.java class. It works fine in my IDE, where all folders are marked as test folders. However when building this project in Maven I get an import error from the Java compiler.

How can I configure Maven to use the Scala test code for Java tests?