supertest가 종료되지 않습니다.

app.spec.js

const app = require('./app');
const request = require('supertest');
const should = require('should');

describe('GET /users は',()=>{
    describe('Success', ()=>{
        it('userオブジェクトを配列で応答する', (done)=> {
            request(app)
                .get('/users')
                .end((err, res)=>{
                    res.body.should.be.instanceOf(Array);
                    done();
                });
        });

        it('limitで指定した数分を返す', (done) => {

            request(app)
                .get('/users?limit=2')
                .end((err, res) => {
                    res.body.should.have.lengthOf(2);
                    done();
                })

        });
        
    });


    describe('Fail', ()=>{
        it('limitが整数型ではない場合は400を返す', (done) => {
            request(app)
                .get('/users?limit=two')
                .expect(400)
                .end(done);
        });
    });

    
});