test.js

const eq = (a, b) => {
  if (a === b) return true
  if (!a || !b) return false
  if (typeof a !== typeof b) return false
  if (typeof a === 'number' && Number.isNaN(a) && Number.isNaN(b)) return true
  if (typeof a === 'object') {
    if (a.constructor !== b.constructor) return false
    const entries = Object.entries(a)
    if (entries.length !== Object.values(b).length) return false
    for (const [k,v] of entries) {
      if (!eq(b[k], v)) return false
    }
    return true
  }
  throw err
}

const tests = []
const tester = f => ({ description, test, expect }) => {
  const count = tests.length + 1
  tests.push(async ctx => {
    try {
      const got = await f(test)(ctx)
      if (!eq(got, expect)) {
        console.log({ got, expect })
        throw Error('Unexpected test result')
      }
      console.log(`PASS #${count} ${description}`)
    } catch (err) {
      console.log(`FAIL #${count} ${description}`)
      const left = tests.length - count
      left && console.log(`...and ${left} ${left > 1 ? 'tests lefts' : 'test left'}`)
      console.log(err.message)
      throw err
    }
    return ctx
  })
}

export const ok = tester(test => test)
export const fail = tester(test => async args => {
  try {
    const err = Error('Should have failed')
    err.result = await test(args)
    return Promise.reject(err)
  } catch ({ message, trace, ...rest }) {
    return { message, ...rest }
  }
})

setTimeout((setup = () => {}) =>
  tests.reduce((q, test) => q.then(test), Promise.resolve(setup()))
    .catch(_ => _))