test.js

import expect from 'expect';
import request from 'supertest';

import app from '../index';

describe('Test for Signup', () => {
  it('should login users', (done) => {
    const userDetail = {
      username: 'christain5',
      password: 'password@1',
    };
    request(app).post('/api/v1/auth/login')
      .send(userDetail)
      .expect(200)
      .expect((res) => {
        expect(res.body.message).toEqual('you have successfully signed in');
        expect(res.body.status).toEqual('Success');
      })
      .end(done);
  });
  
  it('should reject users with empty username', (done) => {
    const userDetail = {
      username: ' ',
      password: 'password@1',
    };
    request(app).post('/api/v1/auth/login')
      .send(userDetail)
      .expect(400)
      .expect((res) => {
        expect(res.body.message).toEqual('invalid username');
      })
      .end(done);
  });
  
  it('should reject users with invalid username format', (done) => {
    const userDetail = {
      username: '1234903TY',
      password: 'password@1',
    };
    request(app).post('/api/v1/auth/login')
      .send(userDetail)
      .expect(400)
      .expect((res) => {
        expect(res.body.message).toEqual('invalid username format');
      })
      .end(done);
  });
  
  it('should reject users with invalid password', (done) => {
    const userDetail = {
      username: 'christain5',
      password: 'password@',
    };
    request(app).post('/api/v1/auth/login')
      .send(userDetail)
      .expect(400)
      .expect((res) => {
        expect(res.body.message).toEqual('invalid password');
      })
      .end(done);
  });
});

Nice one