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Testing Last-Modified Header Management in Koa.js

This test suite evaluates the Last-Modified header functionality in Koa’s response handling. It verifies proper date formatting, string conversion, and header management for HTTP response modification timestamps.

Test Coverage Overview

The test suite provides comprehensive coverage of Last-Modified header operations:

UTCString conversion for header setting
Date string handling and parsing
Date object retrieval and timestamp comparison
Undefined state handling

Implementation Analysis

The testing approach uses Node’s native test framework with focused unit tests. It employs strict assertion patterns to verify header manipulation and date formatting, ensuring precise timestamp handling across different input formats.

The implementation leverages Jest-style describe/it blocks for clear test organization and uses Node’s assert module for validations.

Technical Details

Testing infrastructure includes:

Node.js native test runner
Assert module for validations
Custom response context helper
UTC date string conversions
Millisecond-precision timestamp comparisons

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Isolated test cases with clear descriptions
Edge case handling for undefined states
Precise timestamp comparisons accounting for millisecond precision
Consistent test structure and organization
Proper test helper utilization

koajs/koa

__tests__/response/last-modified.test.js

            
'use strict'

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

describe('res.lastModified', () => {
  it('should set the header as a UTCString', () => {
    const res = response()
    const date = new Date()
    res.lastModified = date
    assert.strictEqual(res.header['last-modified'], date.toUTCString())
  })

  it('should work with date strings', () => {
    const res = response()
    const date = new Date()
    res.lastModified = date.toString()
    assert.strictEqual(res.header['last-modified'], date.toUTCString())
  })

  it('should get the header as a Date', () => {
    // Note: Date() removes milliseconds, but it's practically important.
    const res = response()
    const date = new Date()
    res.lastModified = date
    assert.strictEqual((res.lastModified.getTime() / 1000), Math.floor(date.getTime() / 1000))
  })

  describe('when lastModified not set', () => {
    it('should get undefined', () => {
      const res = response()
      assert.strictEqual(res.lastModified, undefined)
    })
  })
})