def myassert(cond : => Boolean) = {
  try {
    assert(cond)
  } catch { 
    case _ : Throwable => System.exit(1)
  }
}

myassert(collatz(1) == 0)
myassert(collatz(6) == 8)
myassert(collatz(9) == 19)
myassert(collatz(9000) == 47)