the singleton class when run e2e testing with Firebase Authentication x Local Emulator Suite

LocalEmulatorAuth.ts

import * as admin from 'firebase-admin'
import axios from 'axios'

const PROJECT_ID = 'your-project-id'

type FirebaseAuthAPIUser = {
  idToken: string //	新しく作成されたユーザーのFirebaseAuthIDトークン。
  email: string //	新しく作成されたユーザーの電子メール。
  refreshToken: string //	新しく作成されたユーザーのFirebaseAuth更新トークン。
  expiresIn: string //	IDトークンの有効期限が切れる秒数。
  localId: string //	新しく作成されたユーザーのuid。
}

/**
 * Firebase AuthenticationのSeeding用シングルトンクラス
 * テスト用に1ユーザーのみを内部で状態保持する
 *
 * @example
 * await LocalEmulatorAuthSingleton.seed()
 * await LocalEmulatorAuthSingleton.signin()
 * const idToken = LocalEmulatorAuthSingleton.idToken()
 */
class LocalEmulatorAuthSingleton {
  private readonly EMail = 'e2e-user@example.com'
  private readonly Password = 'secretPassword'

  private user: FirebaseAuthAPIUser

  constructor() {
    // エミュレータに接続
    // see:
    // https://firebase.google.com/docs/emulator-suite/connect_auth?hl=ja#android_ios_and_web_sdks
    admin.initializeApp({ projectId: PROJECT_ID })
  }

  seed = async () => {
    await this.clearUser()
    this.user = await this.signup()
    console.log('Successfully created new user')
  }

  /**
   * 既にsignup済みのユーザーアカウントでsigninします
   * https://firebase.google.com/docs/reference/rest/auth?hl=ja#section-sign-in-email-password
   */
  signin = async (): Promise<void> => {
    const payload = {
      email: this.EMail,
      password: this.Password,
      returnSecureToken: true
    }
    const { data } = await axios.post(
      'http://localhost:9099/identitytoolkit.googleapis.com/v1/accounts:signInWithPassword?key=fake-api-key',
      payload
    )

    this.user = data
  }

  uid = () => this.user.localId

  idToken = () => this.user.idToken

  /**
   * https://firebase.google.com/docs/reference/rest/auth?hl=ja#section-create-email-password
   */
  private signup = async (): Promise<FirebaseAuthAPIUser> => {
    const payload = {
      email: this.EMail,
      password: this.Password,
      returnSecureToken: true
    }
    const { data } = await axios.post(
      'http://localhost:9099/identitytoolkit.googleapis.com/v1/accounts:signUp?key=fake-api-key',
      payload
    )

    return data
  }

  /**
   * https://firebase.google.com/docs/reference/rest/auth?hl=ja#section-auth-emulator-clearaccounts
   */
  private clearUser = async () => {
    await axios.delete(
      `http://localhost:9099/emulator/v1/projects/${PROJECT_ID}/accounts`
    )
  }
}

export const LocalEmulatorAuth = new LocalEmulatorAuthSingleton()