Jest&supertest ApI testing returning TypeError: app.address is not a function

The reason is your server passed into supertest is undefined. supertest will use app.address() internally, see this line. That's why it throw an error:

TypeError: app.address is not a function

If you want to import the server dynamically, You should change:

let server;beforeAll(async () => {  server = import('../../../../src/index')})

to:

let server;beforeAll(async () => {  const mod = await import('../../../../src/index');  server = (mod as any).default;});

E.g.

index.ts:

import express from 'express';const app = express();app.post('/api/users/auth/register', (req, res) => {  res.status(400).json({ errArray: [] });});const port = 3001 || process.env.PORT;const server = app.listen(port, () => console.log(`Server running on port ${port}`));export default server;

index.test.ts:

import request from 'supertest';describe('/api/users/auth', () => {  let server;  beforeAll(async () => {    const mod = await import('./');    server = (mod as any).default;  });  afterAll((done) => {    if (server) {      server.close(done);    }  });  it('should return 400 if email is invalid', async () => {    const res = await request(server)      .post('/api/users/auth/register')      .send({        email: 'nomail',        password: 'validpassword123',        name: 'name',      });    expect(res.status).toBe(400);    expect(res.body).toHaveProperty('errArray');  });});

Integration test result with coverage report:

☁  jest-codelab [master] ⚡  npx jest --coverage --verbose /Users/ldu020/workspace/github.com/mrdulin/jest-codelab/src/stackoverflow/54230886/index.test.ts PASS  src/stackoverflow/54230886/index.test.ts (10.306s)  /api/users/auth    ✓ should return 400 if email is invalid (56ms)  console.log src/stackoverflow/54230886/index.ts:437    Server running on port 3001----------|----------|----------|----------|----------|-------------------|File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |----------|----------|----------|----------|----------|-------------------|All files |      100 |       50 |      100 |      100 |                   | index.ts |      100 |       50 |      100 |      100 |                 9 |----------|----------|----------|----------|----------|-------------------|Test Suites: 1 passed, 1 totalTests:       1 passed, 1 totalSnapshots:   0 totalTime:        11.875s

Source code: https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/54230886