passableAsJustin = (passable, shouldIndent = true) => {
  let slotCount = 0;
  // Using post-increment below only so that the indexes start at zero
  // and the `slotCount` variable can be initialized to `0` rather than
  // `-1`.
  // eslint-disable-next-line no-plusplus
  const convertValToSlot = val => `s${slotCount++}`;
  const { toCapData } = makeMarshal(convertValToSlot);
  const { body, slots } = toCapData(passable);
  const encoded = JSON.parse(body);
  return decodeToJustin(encoded, shouldIndent, slots);
}
@param {Passable} passable
@param {boolean} [shouldIndent]
@returns {string}