I have a library written in Python complete with unit tests. I'm about to start porting of the functionality to Scala to run on Spark and as part of an Android application. But I'm loath to reproduce the unit tests in scala. 
Is there a method for exposing the to-be-written Scala library to external interrogation from Python? I can rewrite the tests to use a command line interface, but I wondered if there were other ways.
I have ruled out Jython because it is not compatible with my existing Python 3 library and unit tests.
Short answer: Maybe, but don't. 
Eventually common sense prevailed. I now aim to either use pyspark or port the unit tests across to Scala along with the rest of the library.
Exposing Scala to Python was achievable by generating Scala code that prints specifically what I wanted. Then from Python calling SBT to compile that code and run it and capture the stdout.
I started mocking the scala version of the same api in Python to create these custom scala scripts and by adding in a compilation step for each query it was getting very slow. As I started considering a command line interface or socket based api for my Mocked Scala classes the reality sunk in.
To answer the actual question of running my existing Python unittests, while I think it could still be possible it is not a very good idea.
Scala Testing with Python unittests