Build tests with esbuild, serve them with vercel's serve-handler, then use playwright to open a browser and stream the console back to the node console

tests.ts

// NOTE: we are just assuming _tests is an alright place to render to

export async function buildAndRunTests (cwd: string): Promise<void> {
  const [{ once }] = cliopts.parse(
    ['o, once', 'run the tests and then exit']
  )

  await file.mkdirs(join(cwd, '_tests'))

  await buildBrowserTests(cwd)
  const server = await serve(cwd, { publicPath: '_tests' })

  const port = server.address().port

  if (!once) { clear() }

  const isSuccess = await runTestsInBrowser({ port })

  if (once) {
    server.close()
    process.exit(isSuccess ? 0 : 1)
  } else {
    await watch(cwd, async paths => {
      if (meaningfulFileChange(paths)) {
        clear()
        await buildBrowserTests(cwd)
        await runTestsInBrowser({ port })
      }
    })
  }
}