handle different responses using mocha in nodejs unit testing

my test is getting passed(200 status code), when i passing correct header information. but when i try with wrong info(400 status code), it can't able to handle that error,

this is my code,(here im passing wrong headers info, so response will be status 400 code)

const chai = require('chai');
const expect = require('chai').expect;
const chaiHttp = require('chai-http');
chai.use(chaiHttp);
const main  = require('../server');
let token;
describe('GET USER', function()  {
  this.timeout(50000);
  it('Display info about user and returns a 200 response', (done) => {
    chai.request(main)
    .get('/users')
    .set("Authorization"," ")
    .then(function(response) {
      // Now let's check our response
      expect(response).to.have.status(200);
      done();
    })
    .catch((err)=>{
      expect(err.status).to.be.equal(400)
      done();
    })
  });
});

im getting error like this,

GET USER
(node:28390) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): AssertionError: expected undefined to equal 400
    1) Display info about user and returns a 200 response

  1 failing

  1) GET USER
       Display info about user and returns a 200 response:
     Error: Timeout of 50000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/test/users.test.js)