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Testing Response Header Manipulation in Koa.js

This test suite validates header handling functionality in Koa’s response object, covering both mock and real response scenarios. The tests ensure proper header manipulation, retrieval, and edge cases in the Koa framework’s response handling system.

Test Coverage Overview

The test suite provides comprehensive coverage of response header functionality in Koa.

Key areas tested include:

Header setting and retrieval operations
Compatibility with res.getHeaders() accessor
Real-world header handling in Koa application context
Edge case handling for missing headers

Implementation Analysis

The testing approach utilizes both isolated response object testing and integrated application testing. The suite employs mock responses and actual Koa application instances to validate header behavior.

Notable patterns include:

Direct header manipulation via res.set()
Header access through response.header property
Integration with Koa’s context object
Mock response object handling

Technical Details

Testing infrastructure includes:

Node.js native test runner (node:test)
Supertest for HTTP assertions
Custom test helpers for context creation
Assert module for verification
Koa application instance for integration tests

Best Practices Demonstrated

The test suite exemplifies high-quality testing practices through well-structured test organization and comprehensive coverage.

Notable practices include:

Isolated unit tests for core functionality
Integration tests for real-world scenarios
Edge case handling
Clear test case organization using describe blocks
Consistent assertion patterns

koajs/koa

__tests__/response/header.test.js

            
'use strict'

const { describe, it } = require('node:test')
const assert = require('assert')
const request = require('supertest')
const response = require('../../test-helpers/context').response
const Koa = require('../..')

describe('res.header', () => {
  it('should return the response header object', () => {
    const res = response()
    res.set('X-Foo', 'bar')
    res.set('X-Number', 200)
    assert.deepStrictEqual(res.header, { 'x-foo': 'bar', 'x-number': '200' })
  })

  it('should use res.getHeaders() accessor when available', () => {
    const res = response()
    res.res._headers = null
    res.res.getHeaders = () => ({ 'x-foo': 'baz' })
    assert.deepStrictEqual(res.header, { 'x-foo': 'baz' })
  })

  it('should return the response header object when no mocks are in use', async () => {
    const app = new Koa()
    let header

    app.use(ctx => {
      ctx.set('x-foo', '42')
      header = Object.assign({}, ctx.response.header)
    })

    await request(app.callback())
      .get('/')

    assert.deepStrictEqual(header, { 'x-foo': '42' })
  })

  describe('when res._headers not present', () => {
    it('should return empty object', () => {
      const res = response()
      res.res._headers = null
      assert.deepStrictEqual(res.header, {})
    })
  })
})