如何使用Jest測驗在模擬庫（例如wssocket.readyState）上使用只讀欄位的代碼？

我想用Jest對這個JS代碼進行單元測驗。它使用 ws websocket 庫：

套接字.js

import WebSocket from "ws";

export default class Socket {
    socket = undefined;

    connect(url): void {
        if (this.socket !== undefined && this.socket.readyState === WebSocket.OPEN) {
            throw new Error("Socket is already connected");
        }

        this.socket = new WebSocket(url);
    }
}

我想檢查錯誤是否被拋出。為此，我為套接字創建了一個模擬，然后需要將readyState套接字物件的CLOSED. 問題是這是不可能的，因為它是一個只讀欄位。

測驗：

import Socket from "./Socket";
import WebSocket from "ws";

jest.mock("ws");

it("can connect", () => {
    // Arrange
    const url = "www.someurl.com";
    jest.spyOn(global, "Promise").mockReturnValueOnce({} as Promise<void>);

    const sut = new Socket();

    // Act
    sut.connect(url);

    const webSocket = jest.mocked(WebSocket).mock.instances[0];

    // Set readystate of socket
    webSocket.readyState = WebSocket.CLOSED; // Error here: Cannot assign to 'readyState' because it is a read-only property. ts(2540)

    const action = () => sut.connect(url);

    // Assert
    expect(action).toThrowError(new Error("Socket is already connected"));
});

問題：如何測驗在模擬庫上使用只讀欄位的任何代碼，例如socket.readyState？

編輯：根據上面的請求添加了 mvce。

uj5u.com熱心網友回復：

更好的測驗策略是創建一個測驗 WebSocket 服務器并連接它。這也是官方團隊做的，看一些測驗用例。ws不建議模擬和測驗實作細節。

下面使用 TypeScript 測驗代碼：

socket.ts：

import WebSocket from "ws";

export default class Socket {
  socket!: WebSocket;

  connect(url: string): void {
    if (this.socket !== undefined && this.socket.readyState === WebSocket.OPEN) {
      throw new Error("Socket is already connected");
    }
    this.socket = new WebSocket(url);
  }
}

socket.test.ts：

import WebSocket from "ws";
import Socket from "./socket";

describe('74062437', () => {

  test('should connect the websocket server', (done) => {
    const wss = new WebSocket.Server({ port: 0 }, () => {
      const socket = new Socket()
      socket.connect(`ws://localhost:${(wss.address() as WebSocket.AddressInfo).port}`);

      socket.socket.on('open', () => {
        expect(socket.socket.readyState).toEqual(WebSocket.OPEN);
        socket.socket.close();
      });

      socket.socket.on('close', () => wss.close(done));
    });
  });

  test('should throw error if already connected websocket server', (done) => {
    expect.assertions(2);
    const wss = new WebSocket.Server({ port: 0 }, () => {
      const socket = new Socket();
      socket.connect(`ws://localhost:${(wss.address() as WebSocket.AddressInfo).port}`);

      socket.socket.on('open', () => {
        expect(socket.socket.readyState).toEqual(WebSocket.OPEN);
        expect(() => socket.connect(`ws://localhost:${(wss.address() as WebSocket.AddressInfo).port}`)).toThrowError('Socket is already connected')
        socket.socket.close();
      });

      socket.socket.on('close', () => wss.close(done));
    });
  });
});

測驗結果：

 PASS  stackoverflow/74062437/socket.test.ts (10.964 s)
  74062437
    ? should connect the websocket server (31 ms)
    ? should throw error if already connected websocket server (6 ms)

-----------|---------|----------|---------|---------|-------------------
File       | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
-----------|---------|----------|---------|---------|-------------------
All files  |     100 |      100 |     100 |     100 |                   
 socket.ts |     100 |      100 |     100 |     100 |                   
-----------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        11.784 s

包版本：

"ws": "^8.9.0",
"jest": "^26.6.3"

標籤：javascript单元测试测试开玩笑的嘲弄

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