Jest如何測試WebSocket通信

要使用Jest測試WebSocket通信，你需要模擬WebSocket對象并提供一個模擬的服務器端。以下是一個簡單的示例，展示了如何使用Jest測試WebSocket通信：

1. 首先，安裝ws庫，它是一個WebSocket服務器和客戶端庫：

npm install ws

2. 創建一個簡單的WebSocket服務器：

// server.js
const WebSocket = require('ws');

const server = new WebSocket.Server({ port: 8080 });

server.on('connection', (socket) => {
  socket.on('message', (message) => {
    console.log(`Received message: ${message}`);
    socket.send(`Server received: ${message}`);
  });
});

3. 創建一個WebSocket客戶端，用于與服務器通信：

// client.js
const WebSocket = require('ws');

const socket = new WebSocket('ws://localhost:8080');

socket.on('open', () => {
  socket.send('Hello, Server!');
});

socket.on('message', (message) => {
  console.log(`Received from server: ${message}`);
});

4. 編寫一個Jest測試，模擬WebSocket通信：

// client.test.js
const WebSocket = require('ws');

jest.mock('ws');

describe('WebSocket Client', () => {
  let socket;

  beforeEach(() => {
    socket = new WebSocket('ws://localhost:8080');
  });

  afterEach(() => {
    socket.close();
  });

  test('sends and receives messages', (done) => {
    const mockMessage = 'Hello, Server!';
    const expectedResponse = `Server received: ${mockMessage}`;

    // Mock the WebSocket server
    WebSocket.Server.mockImplementation((options) => {
      expect(options.port).toBe(8080);
      return {
        on: (event, callback) => {
          if (event === 'connection') {
            callback(socket);
          }
        },
      };
    });

    // Mock the WebSocket client
    socket.send = jest.fn();
    socket.on = jest.fn((event, callback) => {
      if (event === 'open') {
        callback();
      } else if (event === 'message') {
        callback(expectedResponse);
      }
    });

    // Initialize the client
    require('./client');

    // Expectations
    expect(socket.send).toHaveBeenCalledWith(mockMessage);
    expect(socket.on).toHaveBeenCalledTimes(2);

    done();
  });
});

5. 運行測試：

npx jest

這個示例展示了如何使用Jest測試WebSocket通信。請注意，這里我們使用了jest.mock()來模擬WebSocket庫，以便在測試中控制WebSocket的行為。