test.js

const firebase = require('firebase')

let func = async () => {
  let app = firebase.initializeApp(require('./firebase.json'))
  let auth = app.auth()
  await auth.signInWithEmailAndPassword(
    'email@example.com', 'xxxxxxx'
  )
  // Do something
  await auth.signOut()
  await app.delete()
}

func().then(() => console.log('done'))