Back to Repositories

Testing Middleware Composition Patterns in Koa.js

This test suite validates the compose functionality in Koa.js middleware system, focusing on both default and configurable composition patterns. It ensures proper middleware execution order and async handling in the request-response cycle.

Test Coverage Overview

The test suite provides comprehensive coverage of Koa’s middleware composition mechanisms:

Default middleware composition flow and execution order
Configurable compose function implementation
Async/await handling in middleware chain
Middleware function sequencing validation

Implementation Analysis

The testing approach utilizes Jest’s describe/it blocks to structure middleware composition tests. It implements supertest for HTTP request simulation and leverages Node’s assert module for validation. The tests specifically verify middleware execution order through an array of sequential calls.

Technical Details

Testing Framework: Node’s built-in test module
HTTP Testing: SuperTest
Assertion Library: Node’s assert module
Test Environment: Node.js runtime
Key Dependencies: Koa.js core library

Best Practices Demonstrated

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

Isolated test cases with clear assertions
Async/await pattern usage
Middleware execution order verification
Custom composition function testing
HTTP response validation

koajs/koa

__tests__/application/compose.test.js

            
'use strict'

const { describe, it } = require('node:test')
const request = require('supertest')
const assert = require('assert')
const Koa = require('../..')

describe('app.compose', () => {
  it('should work with default compose ', async () => {
    const app = new Koa()
    const calls = []

    app.use((ctx, next) => {
      calls.push(1)
      return next().then(() => {
        calls.push(4)
      })
    })

    app.use((ctx, next) => {
      calls.push(2)
      return next().then(() => {
        calls.push(3)
      })
    })

    await request(app.callback())
      .get('/')
      .expect(404)

    assert.deepStrictEqual(calls, [1, 2, 3, 4])
  })

  it('should work with configurable compose', async () => {
    const calls = []
    let count = 0
    const app = new Koa({
      compose (fns) {
        return async (ctx) => {
          const dispatch = async () => {
            count++
            const fn = fns.shift()
            fn && fn(ctx, dispatch)
          }
          dispatch()
        }
      }
    })

    app.use((ctx, next) => {
      calls.push(1)
      next()
      calls.push(4)
    })
    app.use((ctx, next) => {
      calls.push(2)
      next()
      calls.push(3)
    })

    await request(app.callback())
      .get('/')

    assert.deepStrictEqual(calls, [1, 2, 3, 4])
    assert.equal(count, 3)
  })
})