signup.test1.js

const signup = require('./signup')
const db = require('./db')

// Test Case 1
test('若密碼太短則註冊失敗，而且 db.isUserExist 不該被呼叫', async () => {
  // 用 stub 把 db.isUserExist 替換掉
  const stubIsUserExist = sinon.stub(db, 'isUserExist')

  // 給一個超短的 password
  let user = { username: 'larry', password: 'pwd' }

  // 確認註冊失敗、而且 db.isUserExist 沒有被呼叫
  await expect(signup(user)).rejects.toThrowError()
  expect(stubIsUserExist.called).toBe(false)
})