Supertest: How to write tests for API endpoint which posts to another API endpoint?

Question

I am using supertest to test my API endpoints. One my endpoint to which I do a post, does another post to a different endpoint and I get a 404 error even though the endpoint is implemented. This is because I am doing not a listen() in my server which is used by supertest and since supertest is not aware of this endpoint in the test, it seems logical that I get a 404. Doing a listen isn't a wise choice since I have multiple tests in multiple files and I don't want to encounter address already in use error

Once way to solve this problem was to start another server as a pretest before running the test so that the endpoint is available during the test but there should be a better approach.

This is my server

// server.js
const express = require('express')
const app = express()

// Middlewares...
// Routes...
post(/abc) // abc posts to def during the test
post(/def)

module.exports = app

This is start.js which has nothing to do with the test and just does a listen and I use this for local manual testing

// start.js
const app = require('./server.js')
app.listen(3000)

Answer 1

Here is the solution:

server.js:

const express = require('express');
const request = require('request-promise');
const app = express();

app.post('/abc', async (req, res) => {
  const url = req.protocol + '://' + req.get('host');
  const rval = await request.post(`${url}/def`);
  res.send(rval);
});
app.post('/def', (req, res) => {
  res.send('def');
});

module.exports = app;

start.js:

const app = require('./server.js');
const s = app.listen(3000, () => {
  console.log(`HTTP server is listening on http://localhost:${s.address().port}`);
});

server.test.js:

const supertest = require('supertest');
const app = require('./server');

describe('server', () => {
  it('should pass', (done) => {
    supertest(app)
      .post('/abc')
      .expect(200)
      .end((err, res) => {
        if (err) throw err;
        expect(res.text).toBe('def');
        done();
      });
  });
});

Integration test result with coverage report:

 PASS  src/stackoverflow/59090082/server.test.js
  server
    ✓ should pass (54ms)

-----------|----------|----------|----------|----------|-------------------|
File       |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
-----------|----------|----------|----------|----------|-------------------|
All files  |      100 |      100 |      100 |      100 |                   |
 server.js |      100 |      100 |      100 |      100 |                   |
-----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        5.208s, estimated 13s

Source code: https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/59090082