模擬靜態類屬性的問題

我有一堂課應該記錄一些東西。記錄器是這樣定義的。

export class Logger {
  public static client = ClientStrategy.create();

  public async logSth(msg: string) {
    params = {"testThing": msg};
    await Logger.client.updateItem(params);
}

export class ClientStrategy {
  public static create() {
    return new DatabaseClient(); // not important here just a factory, with a method updateItem
  }
}

我試圖在一個開玩笑的測驗中模擬這個。我正在嘗試模擬這個客戶端策略和一個創建方法。但它沒有像我預期的那樣作業。

jest.mock("./ClientStrategy");
const mockClientStrategy = jest.mocked(ClientStrategy, false);

describe("Logger", () => {

    beforeEach(() => {
    jest.spyOn(<any>mockDatabaseClientStrategy, "create").mockImplementation(() => {
      return {
        updateItem: () => {
          return {}
        } 
      };
    });
  });

   
  it("should log sth", async () => {
    const response = await Logger.logSth("testMsg");
    expect(response).not.tobeUndefined();
  });
});

但我得到無法讀取未定義的屬性“logSth”。你能幫我在這里做錯什么嗎？我認為我的模擬應該可以正常作業，但不幸的是我對此沒有定義。

uj5u.com熱心網友回復：

兩者都jest.mock()將jest.spyOn()起作用。但是對于您的情況，無需將它們一起使用。因此，讓我們使用jest.spyOn()來解決您的問題。

由于ClientStrategy.create將在您匯入Logger類時執行，因此您需要ClientStrategy.create在匯入Logger類之前添加 spy on。

此外，該logSth方法是實體方法，而不是類方法。

例如

Logger.ts：

import { ClientStrategy } from './ClientStrategy';

console.log('ClientStrategy.create: ', ClientStrategy.create);
export class Logger {
  public static client = ClientStrategy.create();

  public async logSth(msg: string) {
    const params = { testThing: msg };
    return Logger.client.updateItem(params);
  }
}

Logger.test.ts：

import { ClientStrategy } from './ClientStrategy';
// import { Logger } from './Logger';

describe('Logger', () => {
  let mockClient;
  let Logger: typeof import('./Logger').Logger;
  beforeEach(async () => {
    mockClient = {
      updateItem: jest.fn(),
    };
    jest.spyOn(ClientStrategy, 'create').mockReturnValue(mockClient);
    Logger = await import('./Logger').then((m) => m.Logger);
  });
  afterEach(() => {
    jest.restoreAllMocks();
  });

  it('should log sth', async () => {
    mockClient.updateItem.mockResolvedValueOnce('fake value');
    const logger = new Logger();
    const response = await logger.logSth('testMsg');
    expect(response).toEqual('fake value');
  });
});

ClientStrategy.ts：

export class ClientStrategy {
  public static create() {
    return { updateItem: async (params) => 'real value' };
  }
}

測驗結果：

 PASS  stackoverflow/71938329/Logger.test.ts
  Logger
    ? should log sth (22 ms)

  console.log
    ClientStrategy.create:  [Function: mockConstructor] {
      _isMockFunction: true,
      getMockImplementation: [Function (anonymous)],
      mock: [Getter/Setter],
      mockClear: [Function (anonymous)],
      mockReset: [Function (anonymous)],
      mockRestore: [Function (anonymous)],
      mockReturnValueOnce: [Function (anonymous)],
      mockResolvedValueOnce: [Function (anonymous)],
      mockRejectedValueOnce: [Function (anonymous)],
      mockReturnValue: [Function (anonymous)],
      mockResolvedValue: [Function (anonymous)],
      mockRejectedValue: [Function (anonymous)],
      mockImplementationOnce: [Function (anonymous)],
      mockImplementation: [Function (anonymous)],
      mockReturnThis: [Function (anonymous)],
      mockName: [Function (anonymous)],
      getMockName: [Function (anonymous)]
    }

      at Object.<anonymous> (stackoverflow/71938329/Logger.ts:3:9)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        2.57 s, estimated 11 s

您可以取消注釋該import { Logger } from './Logger';陳述句并注釋import()以檢查日志。您將看到未模擬的ClientStrategy.create方法：

console.log
    ClientStrategy.create:  [Function: create]

標籤：javascript 单元测试 开玩笑的 嘲弄 开玩笑

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