Base64 encoding and back in scala

bla.scala

    "prove encoding is a thing" in new Context {
      val originalStr = "tschüß"
      val base64EncodedStr = Base64.getEncoder.encodeToString(originalStr.getBytes("UTF-8"))
      val decodedStr = new String(Base64.getDecoder().decode(base64EncodedStr), "ASCII")

      decodedStr ==== originalStr
    }

'tsch����' is not equal to 'tschüß'
Expected :tschüß
Actual   :tsch����

Of cause this won't work, it is encoding as UTF-8 and decoding using ASCII.