How can I test middleware in Express.js?

How can I test middleware in Express.js?

You can test middleware in Express.js using tools like Mocha, Chai, or Jest. Would you like a code example?

Yes, please provide a code example.

Sure! Here's a simple example using Mocha and Chai:

const request = require('supertest');
const express = require('express');
const app = express();

const myMiddleware = (req, res, next) => {
    req.customProperty = 'Hello, World!';
    next();
};

app.use(myMiddleware);

app.get('/', (req, res) => {
    res.send(req.customProperty);
});

describe('Middleware Test', () => {
    it('should add customProperty to the request', (done) => {
        request(app)
            .get('/')
            .expect(200)
            .expect('Hello, World!', done);
    });
});

This tests if the middleware correctly adds a property to the request.

What if I want to test error handling in middleware?

You can simulate an error in your middleware and check if the error handling works as expected. Would you like an example?