Я снова просмотрел документацию после ответа Марио и, похоже, на самом деле есть встроенная функциональность для вариантов использования, подобных моему
http://www.scalatest.org/user_guide/using_scalatest_with_sbt
Using Reporters
You can use ScalaTest's reporters by specifying the passing the following arguments to ScalaTest:
-f[configs...] <filename> - causes test results to be written to the named file
-u <directory> - causes test results to be written to junit-style xml files in the named directory
-h <directory> [-Y ] - causes test results to be written to HTML files in the named directory, optionally included the specified CSS file
-a <number of files to archive> - causes specified number of old summary and durations files to be archived (in summaries/ and durations/ subdirectories) for dashboard reporter (default is two)
-o[configs...] - causes test results to be written back to sbt, which usually displays it on the standard output
-e[configs...] - causes test results to be written to the standard error
-k <host> <port> - causes test results to be written to socket in the named host and port number, using XML format
-K <host> <port> - causes test results to be written to socket in the named host and port number, using Java object binary format
-C[configs...] <reporterclass> - causes test results to be reported to an instance of the specified fully qualified Reporter class name