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Testing Content Type Validation Implementation in Koa

This test suite validates the content type checking functionality in Koa’s request context using the ctx.is() method. It thoroughly examines MIME type matching and content type validation across various scenarios and input formats.

Test Coverage Overview

The test suite provides comprehensive coverage of content type validation scenarios in Koa.

Key areas tested include:

MIME type parameter handling
Empty body scenarios
Missing content type cases
Single and multiple type matching
URL-encoded content handling

Implementation Analysis

The testing approach uses Jest’s describe/it blocks to organize test cases hierarchically. Each scenario validates the ctx.is() method’s behavior with different content-type headers and input patterns.

The implementation leverages Node’s native test framework with assert for validations and uses custom test helpers for context creation.

Technical Details

Testing tools and setup:

Node.js test runner
Assert module for assertions
Custom context test helpers
Jest-style test organization
Strict mode JavaScript

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Comprehensive edge case coverage
Consistent test structure and organization
Clear test case descriptions
Isolated test contexts
Thorough type matching validation

koajs/koa

__tests__/request/is.test.js

            
'use strict'

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

describe('ctx.is(type)', () => {
  it('should ignore params', () => {
    const ctx = context()
    ctx.header['content-type'] = 'text/html; charset=utf-8'
    ctx.header['transfer-encoding'] = 'chunked'

    assert.strictEqual(ctx.is('text/*'), 'text/html')
  })

  describe('when no body is given', () => {
    it('should return null', () => {
      const ctx = context()

      assert.strictEqual(ctx.is(), null)
      assert.strictEqual(ctx.is('image/*'), null)
      assert.strictEqual(ctx.is('image/*', 'text/*'), null)
    })
  })

  describe('when no content type is given', () => {
    it('should return false', () => {
      const ctx = context()
      ctx.header['transfer-encoding'] = 'chunked'

      assert.strictEqual(ctx.is(), false)
      assert.strictEqual(ctx.is('image/*'), false)
      assert.strictEqual(ctx.is('text/*', 'image/*'), false)
    })
  })

  describe('give no types', () => {
    it('should return the mime type', () => {
      const ctx = context()
      ctx.header['content-type'] = 'image/png'
      ctx.header['transfer-encoding'] = 'chunked'

      assert.strictEqual(ctx.is(), 'image/png')
    })
  })

  describe('given one type', () => {
    it('should return the type or false', () => {
      const ctx = context()
      ctx.header['content-type'] = 'image/png'
      ctx.header['transfer-encoding'] = 'chunked'

      assert.strictEqual(ctx.is('png'), 'png')
      assert.strictEqual(ctx.is('.png'), '.png')
      assert.strictEqual(ctx.is('image/png'), 'image/png')
      assert.strictEqual(ctx.is('image/*'), 'image/png')
      assert.strictEqual(ctx.is('*/png'), 'image/png')

      assert.strictEqual(ctx.is('jpeg'), false)
      assert.strictEqual(ctx.is('.jpeg'), false)
      assert.strictEqual(ctx.is('image/jpeg'), false)
      assert.strictEqual(ctx.is('text/*'), false)
      assert.strictEqual(ctx.is('*/jpeg'), false)
    })
  })

  describe('given multiple types', () => {
    it('should return the first match or false', () => {
      const ctx = context()
      ctx.header['content-type'] = 'image/png'
      ctx.header['transfer-encoding'] = 'chunked'

      assert.strictEqual(ctx.is('png'), 'png')
      assert.strictEqual(ctx.is('.png'), '.png')
      assert.strictEqual(ctx.is('text/*', 'image/*'), 'image/png')
      assert.strictEqual(ctx.is('image/*', 'text/*'), 'image/png')
      assert.strictEqual(ctx.is('image/*', 'image/png'), 'image/png')
      assert.strictEqual(ctx.is('image/png', 'image/*'), 'image/png')

      assert.strictEqual(ctx.is(['text/*', 'image/*']), 'image/png')
      assert.strictEqual(ctx.is(['image/*', 'text/*']), 'image/png')
      assert.strictEqual(ctx.is(['image/*', 'image/png']), 'image/png')
      assert.strictEqual(ctx.is(['image/png', 'image/*']), 'image/png')

      assert.strictEqual(ctx.is('jpeg'), false)
      assert.strictEqual(ctx.is('.jpeg'), false)
      assert.strictEqual(ctx.is('text/*', 'application/*'), false)
      assert.strictEqual(ctx.is('text/html', 'text/plain', 'application/json; charset=utf-8'), false)
    })
  })

  describe('when Content-Type: application/x-www-form-urlencoded', () => {
    it('should match "urlencoded"', () => {
      const ctx = context()
      ctx.header['content-type'] = 'application/x-www-form-urlencoded'
      ctx.header['transfer-encoding'] = 'chunked'

      assert.strictEqual(ctx.is('urlencoded'), 'urlencoded')
      assert.strictEqual(ctx.is('json', 'urlencoded'), 'urlencoded')
      assert.strictEqual(ctx.is('urlencoded', 'json'), 'urlencoded')
    })
  })
})