Comment for test

commentTest.js

import chai from 'chai';
import chaiHttp from 'chai-http';
import server from '../index.js';

chai.should();

chai.use(chaiHttp);
let clinentToken;
describe('Tests for comments', () => {
  it('should login ', (done) => {
    const cred = {
      username: 'clet',
      password: '1234',
    };
    chai.request(server)
      .post('/api/v1/auth/login')
      .send(cred)
      .then((res) => {
        clientToken = res.body.token;
      });
  });
  it('should create a comment', (done) => {
    const comment = {
      body: 'It takes a Jacobian',
    };
    chai.request(server)
      .post('/api/articles/1/comments')
      .send(comment)
      .set('Authorization', `Bearer, ${clientToken}`)
      .end((err, res) => {
        res.should.have.status(201);
        res.body.should.be.a('object');
        res.body.should.have.property('comment');
        res.body.comment.should.have.property('createdAt').eql('2016-02-18T03:22:56.637Z');
        res.body.comment.should.have.property('updatedAt').eql('2016-02-18T03:22:56.637Z');
        res.body.comment.should.have.property('body').eql('It takes a Jacobian');
        res.body.comment.author.should.be.a('object');
        res.body.comment.author.should.have.property('username').eql('It takes a Jacobian');
        res.body.comment.author.should.have.property('bio').eql('jake');
        res.body.comment.author.should.have.property('image').eql('https://i.stack.imgur.com/xHWG8.jpg');
        res.body.comment.author.should.have.property('following').eql(false);
        done(err);
      });
  });
});

You should test values in the sent variable not rewrite the value but reference the variable values.