class ParallelTests::Test::Runner

def set_unknown_runtime(tests, options)

NOTE: an optimization could be doing runtime by average runtime per file size, but would need file checks
fill gaps with unknown-runtime if given, average otherwise 
def set_unknown_runtime(tests, options)
  known, unknown = tests.partition(&:last)
  return if unknown.empty?
  unknown_runtime = options[:unknown_runtime] ||
    (known.empty? ? 1 : known.map!(&:last).sum / known.size) # average
  unknown.each { |set| set[1] = unknown_runtime }
end