How to write the Unit test cases for Node JS application which uses kafka-node and HTTP call in a single file?

Question

Below is my sample code. Could someone please tell me how to start the Unit test code for testing and coverage?

const kafka = require('kafka-node');
const express = require('express');
const app = express();
app.use(express.json());
app.use(express.urlencoded({ extended: true }));

const { EventGenerator } = require('../src/index');

const client = new kafka.KafkaClient({ kafkahost: process.env.KAFKA_LISTENERS });
const producer = new kafka.Producer(client);

producer.on('ready', ()=>{
   app.post(URL, function(req, res) {
   console.log(req.body);
    //code goes on....`

I tried using Jest framework for writing some sample code. But it's not worked.