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Testing Language Acceptance Handling in Koa Framework

This test suite validates the language acceptance functionality in Koa’s request handling system. It focuses on testing the ctx.acceptsLanguages() method which determines client language preferences based on Accept-Language headers and handles language negotiation.

Test Coverage Overview

The test suite provides comprehensive coverage of the acceptsLanguages functionality.

Key areas tested include:

Empty argument handling with populated Accept-Language headers
Multiple language argument processing
Best-fit language selection
Array-based language preference handling
Fallback behavior when Accept-Language is not present

Implementation Analysis

The testing approach uses Node’s native test framework with describe/it blocks for structured test organization. It implements isolated context creation for each test case using test helpers, ensuring clean test environments.

The tests utilize assertion patterns to verify language preference ordering, matching logic, and fallback behaviors. The implementation demonstrates proper use of request header manipulation and assertion chaining.

Technical Details

Testing tools and configuration:

Node.js native test framework (node:test)
Assert module for assertions
Custom context test helpers
Mock request headers for Accept-Language testing
Strict mode JavaScript execution

Best Practices Demonstrated

The test suite exemplifies several testing best practices in Node.js applications.

Notable practices include:

Isolated test contexts for each scenario
Hierarchical test organization using nested describe blocks
Comprehensive edge case coverage
Clear test case descriptions
Consistent assertion patterns

koajs/koa

__tests__/request/acceptsLanguages.test.js

            
'use strict'

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

describe('ctx.acceptsLanguages(langs)', () => {
  describe('with no arguments', () => {
    describe('when Accept-Language is populated', () => {
      it('should return accepted types', () => {
        const ctx = context()
        ctx.req.headers['accept-language'] = 'en;q=0.8, es, pt'
        assert.deepStrictEqual(ctx.acceptsLanguages(), ['es', 'pt', 'en'])
      })
    })
  })

  describe('with multiple arguments', () => {
    describe('when Accept-Language is populated', () => {
      describe('if any types types match', () => {
        it('should return the best fit', () => {
          const ctx = context()
          ctx.req.headers['accept-language'] = 'en;q=0.8, es, pt'
          assert.strictEqual(ctx.acceptsLanguages('es', 'en'), 'es')
        })
      })

      describe('if no types match', () => {
        it('should return false', () => {
          const ctx = context()
          ctx.req.headers['accept-language'] = 'en;q=0.8, es, pt'
          assert.strictEqual(ctx.acceptsLanguages('fr', 'au'), false)
        })
      })
    })

    describe('when Accept-Language is not populated', () => {
      it('should return the first type', () => {
        const ctx = context()
        assert.strictEqual(ctx.acceptsLanguages('es', 'en'), 'es')
      })
    })
  })

  describe('with an array', () => {
    it('should return the best fit', () => {
      const ctx = context()
      ctx.req.headers['accept-language'] = 'en;q=0.8, es, pt'
      assert.strictEqual(ctx.acceptsLanguages(['es', 'en']), 'es')
    })
  })
})