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Testing Subdomain Processing Implementation in koajs/koa

This test suite validates subdomain handling functionality in Koa.js request objects, focusing on extracting and processing subdomain arrays from host headers. It ensures proper subdomain parsing across different configurations and edge cases.

Test Coverage Overview

The test suite provides comprehensive coverage of subdomain extraction functionality:

Validates multi-level subdomain parsing with configurable offset
Tests empty host header scenarios
Verifies IP address handling with ports
Covers edge cases in hostname processing

Implementation Analysis

The testing approach utilizes Node’s native test framework with assert module for verification. It implements isolated request object testing through mock contexts, allowing granular control over header values and application configuration.

The tests follow a clear pattern of request object setup, header manipulation, and assertion verification.

Technical Details

Testing tools and configuration:

Node.js native test framework
Assert module for assertions
Custom test helpers for request context creation
Mock request objects with configurable headers
Subdomain offset configuration testing

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Isolated test cases with clear separation of concerns
Comprehensive edge case coverage
Consistent test structure and organization
Effective use of mock objects
Clear assertion messages and expectations

koajs/koa

__tests__/request/subdomains.test.js

            
'use strict'

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

describe('req.subdomains', () => {
  it('should return subdomain array', () => {
    const req = request()
    req.header.host = 'tobi.ferrets.example.com'
    req.app.subdomainOffset = 2
    assert.deepStrictEqual(req.subdomains, ['ferrets', 'tobi'])

    req.app.subdomainOffset = 3
    assert.deepStrictEqual(req.subdomains, ['tobi'])
  })

  it('should work with no host present', () => {
    const req = request()
    assert.deepStrictEqual(req.subdomains, [])
  })

  it('should check if the host is an ip address, even with a port', () => {
    const req = request()
    req.header.host = '127.0.0.1:3000'
    assert.deepStrictEqual(req.subdomains, [])
  })
})