TDD for Authors' Haven - Team Elven

user.test.js

import chai from 'chai';
import supertest from 'supertest';
import app from '../app';

const request = supertest(app);
const { expect } = chai;

// existing user email
// invalid email
// password of length less than 8
// password not being alphanumeric
// successful sign up

describe('Test user API', () => {
  it('should return a status 400 error if email already exist', (done) => {
      request
        .post('/api/users')
        .set('Content-type', 'application/json')
        .send({
          username: 'Fayokemi',
          email: '[email protected]',
          password: 'signup49test',
        })
        .end((err, res) => {
          expect(res.status).to.equal(400);
          expect(res.body).to.be.an('object');
          expect(res.body).to.haveOwnProperty('errors').to.be.an('array');
          expect(res.body.errors.email[0]).to.equal('The email you have entered already exist');
          done();
        });
    });
  
  it('should return a status 400 error response for invalid email format', (done) => {
      request
        .post('/api/users')
        .set('Content-type', 'application/json')
        .send({
          username: 'Fayokemi',
          email: 'fayoarightcom',
          password: 'signup49test',
        })
        .end((err, res) => {
          expect(res.status).to.equal(400);
          expect(res.body).to.be.an('object');
          expect(res.body).to.be.an('array');
          expect(res.body.errors.email[1]).to.equal('The email you have entered is invalid');
          done();
        });
    });
  
  it('should return a status 400 error if the password length is less than 8', (done) => {
      request
        .post('/api/users')
        .set('Content-type', 'application/json')
        .send({
          username: 'Fayokemi',
          email: '[email protected]',
          password: 'sign',
        })
        .end((err, res) => {
          expect(res.status).to.equal(400);
          expect(res.body).to.be.an('object');
          expect(res.body).to.haveOwnProperty('errors').to.be.an('array');
          expect(res.body.errors.password[0]).to.equal('Password length may not be less than 8');
          done();
        });
    });
  
   it('should return a status 400 error if the password is not Alphanumeric', (done) => {
      request
        .post('/api/users')
        .set('Content-type', 'application/json')
        .send({
          username: 'Fayokemi',
          email: '[email protected]',
          password: 'signeduptoday',
        })
        .end((err, res) => {
          expect(res.status).to.equal(400);
          expect(res.body).to.be.an('object');
          expect(res.body.errors).to.be.an('array');
          expect(res.body).to.haveOwnProperty('errors').to.be.an('array');
          expect(res.body.errors.password[1]).to.equal('The password field should contain both letters and numerals');
          done();
        });
    });
  
   it('should return a status 200 for successfully signing up', (done) => {
     
     let username;
     let firstName;
     let password;
     
      request
        .post('/api/users')
        .set('Content-type', 'application/json')
        .send({
          username: 'Fayokemi',
          email: '[email protected]',
          password: 'signed49test7',
        })
        .end((err, res) => {
          expect(res.status).to.equal(400);
          expect(res.body).to.be.an('object');
          expect(res.body).to.haveOwnProperty('message').to.equal(`Success signing up ${username}`);
          expect(res.body.email).to.equal(`${email}`);
          expect(res.body.password).to.equal(`${password}`);
          done();
        });
    });
})

A good job and in-depth test.
Just like observations made by Veraclins and yomigeek, I also feel your error messages are lengthy.
In your last test, you created three variables and used them in the string literal to return a personified message to the user. I feel you can also send the values in the variables to the server. But then you never assigned values to the variables.

Good job on the test.
Echoing what everybody else has said, I feel the responses are too wordy. Try and make then more concise next time.