public/js/tests/test.mjs

import { join as joinPath, dirname } from 'path'
import { fileURLToPath } from 'url'
import { deepStrictEqual } from 'assert'
import * as fs from 'fs'
const { readFile, writeFile } = fs.promises

global.window = global
global.fetch = url => {
  // this is a fake implementation of fetch for the tester
  // -> refer to https://devdocs.io/javascript/global_objects/fetch
  const accessBody = async () => { throw Error('body unavailable') }
  return {
    ok: false,
    type: 'basic',
    status: 500,
    statusText: 'Internal Server Error',
    json: accessBody,
    text: accessBody,
  }
}

const wait = delay => new Promise(s => setTimeout(s, delay))
const fail = fn => { try { fn() } catch (err) { return true } }

const props = [String,Array]
  .flatMap(({ prototype }) =>
    Object.getOwnPropertyNames(prototype)
      .map(key => ({ key, value: prototype[key], src: prototype })))
  .filter(p => typeof p.value === 'function')

const eq = (a, b) => {
  const changed = []
  for (const p of props) { !p.src[p.key] && (changed[changed.length] = p) }
  for (const p of changed) { p.src[p.key] = p.value }
  deepStrictEqual(a, b)
  for (const p of changed) { p.src[p.key] = undefined }
  return true
}

const [submitPath, name] = process.argv.slice(2)
const fatal = (...args) => {
  console.error(...args)
  process.exit(1)
}

if (!name) fatal('missing exercise, usage:\nnode test exercise-name')

const ifNoEnt = fn => err => {
  if (err.code !== 'ENOENT') throw err
  fn(err)
}

const root = dirname(fileURLToPath(import.meta.url))
const read = (filename, description) =>
  readFile(filename, 'utf8').catch(
    ifNoEnt(() => fatal(`Missing ${description} for ${name}`)),
  )

const readTest = filename =>
  readFile(filename, 'utf8').then(test => ({
    test,
    mode: filename.endsWith('.js') ? 'function' : 'node',
  }))

const stackFmt = (err, url) => {
  for (const p of props) { p.src[p.key] = p.value }
  if (err instanceof Error) return err.stack.split(url).join(`${name}.js`)
  throw Error(`Unexpected type thrown: ${typeof err}. usage: throw Error('my message')`)  
}

const any = arr =>
  new Promise(async (s, f) => {
    let firstError
    const setError = err => firstError || (firstError = err)
    await Promise.all(arr.map(p => p.then(s, setError)))
    f(firstError)
  })

const testNode = async ({ test, name }) => {
  const path = `${submitPath}/${name}.mjs`
  return {
    path,
    url: joinPath(root, `${name}_test.mjs`),
    code: await read(path, 'student solution'),
  }
}

const runTests = async ({ url, path, code }) => {
  const { setup, tests } = await import(url).catch(err =>
    fatal(`Unable to execute ${name} solution, error:\n${stackFmt(err, url)}`),
  )

  const ctx = (await (setup && setup())) || {}
  const tools = { eq, fail, wait, code, ctx, path }
  for (const [i, t] of tests.entries()) {
    try {
      if (!(await t(tools))) {
        throw Error('Test failed')
      }
    } catch (err) {
      console.log(`test #${i+1} failed:\n${t.toString()}\n\nError:`)
      fatal(stackFmt(err, url))
    }
  }
  console.log(`${name} passed (${tests.length} tests)`)
}

const main = async () => {
  const { test, mode } = await any([
    readTest(joinPath(root, `${name}_test.js`)),
    readTest(joinPath(root, `${name}_test.mjs`)),
  ]).catch(ifNoEnt(() => fatal(`Missing test for ${name}`)))

  if (mode === "node") return runTests(await testNode({ test, name }))
  const path = `${submitPath}/${name}.js`
  const rawCode = await read(path, "student solution")

  // this is a very crude and basic removal of comments
  // since checking code is only use to prevent cheating
  // it's not that important if it doesn't work 100% of the time.
  const code = rawCode.replace(/\/\*[\s\S]*?\*\/|\/\/.*/g, "").trim()
  if (code.includes("import")) fatal("import keyword not allowed")

  const parts = test.split("// /*/ // ⚡")
  const [inject, testCode] = parts.length < 2 ? ["", test] : parts
  const combined = `${inject.trim()}\n${rawCode
    .replace(inject.trim(), "")
    .trim()}\n${testCode.trim()}\n`

  const b64 = Buffer.from(combined).toString("base64")
  const url = `data:text/javascript;base64,${b64}`
  return runTests({ path, code, url })
}

main().catch(err => fatal(err.stack))