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Testing Context JSON Serialization in Koa.js

This test suite validates the JSON serialization functionality of Koa’s context object, ensuring proper conversion of request and response data. It verifies that the ctx.toJSON() method correctly represents the HTTP context with all relevant properties and headers.

Test Coverage Overview

The test coverage focuses on the serialization of Koa’s context object to JSON format.

Key areas tested include:

Request properties (method, URL, headers)
Response properties (status, message, headers)
Content-type and content-length handling
Proper structure of serialized JSON output

Implementation Analysis

The testing approach uses Node’s native test framework with assertion-based validation. The implementation leverages the test-helpers/context utility for creating isolated context instances, demonstrating a clean pattern for Koa middleware testing.

The test employs JSON.parse/stringify operations to verify the complete serialization cycle.

Technical Details

Testing tools and configuration:

Node.js native test runner (node:test)
Native assert module for assertions
Custom context test helper
JSON serialization/deserialization methods
HTTP request/response mocking

Best Practices Demonstrated

The test exhibits several quality testing practices in Node.js middleware testing.

Notable practices include:

Isolated test context creation
Comprehensive property verification
Deep equality checks for nested objects
Clear test case organization
Proper HTTP header handling verification

koajs/koa

__tests__/context/toJSON.test.js

            
'use strict'

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

describe('ctx.toJSON()', () => {
  it('should return a json representation', () => {
    const ctx = context()

    ctx.req.method = 'POST'
    ctx.req.url = '/items'
    ctx.req.headers['content-type'] = 'text/plain'
    ctx.status = 200
    ctx.body = '<p>Hey</p>'

    const obj = JSON.parse(JSON.stringify(ctx))
    const req = obj.request
    const res = obj.response

    assert.deepStrictEqual({
      method: 'POST',
      url: '/items',
      header: {
        'content-type': 'text/plain'
      }
    }, req)

    assert.deepStrictEqual({
      status: 200,
      message: 'OK',
      header: {
        'content-type': 'text/html; charset=utf-8',
        'content-length': '10'
      }
    }, res)
  })
})