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Testing Content-Type Response Handling in koajs/koa

This test suite validates the Content-Type handling functionality in Koa’s response module, covering both setting and retrieving content types with various MIME types and charset configurations. The tests ensure proper handling of content type extensions, charset defaults, and edge cases.

Test Coverage Overview

The test suite provides comprehensive coverage of Content-Type manipulation in Koa responses. It examines:

Direct MIME type setting and retrieval
Extension-based content type resolution
Charset handling and defaults
Edge cases with unknown content types
Empty content type scenarios

Implementation Analysis

The testing approach uses Node’s built-in test framework with a context-based pattern. Tests are organized using nested describe blocks for clear categorization of test scenarios. Each test case follows the Arrange-Act-Assert pattern, utilizing a fresh context instance for isolation.

The implementation leverages Node’s assert module for assertions and custom test helpers for context creation.

Technical Details

Testing tools and configuration include:

Node.js test runner (node:test)
Custom context test helpers
Node’s assert module for validations
Strict mode JavaScript execution
Nested describe/it blocks for test organization

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Isolation of test cases using fresh contexts
Comprehensive coverage of edge cases
Clear test case organization and naming
Consistent assertion patterns
Proper setup and teardown management

koajs/koa

__tests__/response/type.test.js

            
'use strict'

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

describe('ctx.type=', () => {
  describe('with a mime', () => {
    it('should set the Content-Type', () => {
      const ctx = context()
      ctx.type = 'text/plain'
      assert.strictEqual(ctx.type, 'text/plain')
      assert.strictEqual(ctx.response.header['content-type'], 'text/plain; charset=utf-8')
    })
  })

  describe('with an extension', () => {
    it('should lookup the mime', () => {
      const ctx = context()
      ctx.type = 'json'
      assert.strictEqual(ctx.type, 'application/json')
      assert.strictEqual(ctx.response.header['content-type'], 'application/json; charset=utf-8')
    })
  })

  describe('without a charset', () => {
    it('should default the charset', () => {
      const ctx = context()
      ctx.type = 'text/html'
      assert.strictEqual(ctx.type, 'text/html')
      assert.strictEqual(ctx.response.header['content-type'], 'text/html; charset=utf-8')
    })
  })

  describe('with a charset', () => {
    it('should not default the charset', () => {
      const ctx = context()
      ctx.type = 'text/html; charset=foo'
      assert.strictEqual(ctx.type, 'text/html')
      assert.strictEqual(ctx.response.header['content-type'], 'text/html; charset=foo')
    })
  })

  describe('with an unknown extension', () => {
    it('should not set a content-type', () => {
      const ctx = context()
      ctx.type = 'asdf'
      assert(!ctx.type)
      assert(!ctx.response.header['content-type'])
    })
  })
})

describe('ctx.type', () => {
  describe('with no Content-Type', () => {
    it('should return ""', () => {
      const ctx = context()
      assert(!ctx.type)
    })
  })

  describe('with a Content-Type', () => {
    it('should return the mime', () => {
      const ctx = context()
      ctx.type = 'json'
      assert.strictEqual(ctx.type, 'application/json')
    })
  })
})