Nodemailer testing without actually send Email

nodemailer_spy.js

const Lab = require("@hapi/lab");
const { expect } = require("chai");
const sinon = require("sinon");
const nodemailer = require("nodemailer");

const { PASS_MAIL, USER_MAIL } = process.env;
const { init } = require("../server_test");

const {
  describe, it, beforeEach, afterEach,
} = exports.lab = Lab.script();

describe("POST /slik/create", () => {
  let token;
  let server;
  let sendMailSpy;
  beforeEach(async () => {
    server = await init(); // Inisialisasi server Hapi
    const options = {
      method: "POST",
      url: "/auth/signin",
      payload: {
        username: "82292319224",
        password: "password",
      },
    };
    const res = await server.inject(options);
    token = res.result.token;

    const transporter = nodemailer.createTransport({
      service: "gmail",
      auth: {
        user: USER_MAIL,
        pass: PASS_MAIL,
      },
    });
    sendMailSpy = sinon.spy(transporter, "sendMail");
  });

  afterEach(async () => {
    await server.stop(); // Menghentikan server Hapi
    sendMailSpy.restore();
  });

  it("should create a new Slik Request & send Email", async () => {
    const payload = {};
    const response = await server.inject({
      url: "/book/dummy/create",
      method: "POST",
      headers: {
        Authorization: `Bearer ${token}`,
      },
      payload,
    });
    expect(response.statusCode).to.equal(201);
    // sinon.assert.called(sendMailSpy);

    // Verifikasi operasi database melalui test-double
    // expect(dbStub.calledOnce).to.be.true();
    // expect(dbStub.getCall(0).args[0]).to.equal(payload);
  });
});

service_book_code.js

// routes
{
        method: "POST",
        path: "/book/dummy/create",
        config: Slik.createDummy,
},
// controller        
module.exports.createDummy = async (request, h) => {
    console.log("create record");
    // ?
    console.log("send email");
    const nameList = ["Riansyah Tohamba"];
    const mailList = ["riansyah.tohamba@kendari.com"];
  
    const noLetter = "book/12/232";
    const replacements = {
      title: "New Request  requested to you",
      username: nameList,
      header: "New  Request need your review.",
      bodyText: `New  with number of letter: ${noLetter} has been created and request approved by you, Please click button bellow for more details`,
      link: `${LOCAL_URL}/dashboard/request/10/detail`,
    };
    const subject = `New Request  has been created with number: ${noLetter}`;
    // attachment is null in create  request
    const emailRes = await sendEmail(h, replacements, subject, mailList);
    if (emailRes.messageId !== undefined) {
      return h.response({
        emailNotif: `Email has sent: ${emailRes.messageId}`,
        message: "create  dummy success",
      }).code(201);
    }
    // ini case dimana email gagal send karene network dan sebagainya
    return emailRes;
  };