where test-suite-by-suite is the following :

#!/usr/bin/env bash

set -eEux

dir=$1

suites=$(find ${dir} \
        -name "*Spec.scala" -printf "%P\n" -or \
        -name "*Test.scala" -printf "%P\n" | sed -r 's@/@.@g ; s/\.scala$//g')

for s in $suites; do
    ./pants test.junit --test=$s --output-mode=ALL ${dir}
done