old_contents: const assert = require('assert')
  const SLOT = 36
  
  module.exports = () => (bot, done) => {
    const Item = require('prismarine-item')(bot.version)
  
    const item1 = new Item(1, 1, 0)
    const item2 = new Item(2, 1, 0)
  
    bot.creative.setInventorySlot(SLOT, item1, (err) => {
      assert.ok(err instanceof Error, 'The error has not been passed')
      assert.ok(bot.inventory.slots[SLOT] == null)
    })
  
    bot.creative.setInventorySlot(SLOT, item2, (err) => {
      assert.ifError(err)
      assert.ok(bot.inventory.slots[SLOT] != null)
      assert.ok(bot.inventory.slots[SLOT].type === item2.type)
      done()
    })
  }
  
new_contents: const assert = require('assert')
  const SLOT = 36
  
  module.exports = () => (bot, done) => {
    const Item = require('prismarine-item')(bot.version)
  
    const item1 = new Item(1, 1, 0)
    const item2 = new Item(2, 1, 0)
  
    let firstCallbackFired = false
    bot.creative.setInventorySlot(SLOT, item1, (err) => {
      assert.ok(err instanceof Error, 'The error has not been passed')
      assert.ok(bot.inventory.slots[SLOT] == null)
      firstCallbackFired = true
    })
  
    bot.creative.setInventorySlot(SLOT, item2, (err) => {
      assert.ifError(err)
      assert.ok(bot.inventory.slots[SLOT] != null)
      assert.ok(bot.inventory.slots[SLOT].type === item2.type)
      assert.ok(firstCallbackFired)
  
      done()
    })
  }
  
subject: Add more conditions to creative test