Jest中mockResolvedValueOnce一次性实现跨测试残留问题

我在为处理SNS主题通知的AWS Lambda编写测试：当特定特性标志关闭时，Lambda会直接返回。但测试1的mock实现会残留到测试2，导致本该正常通过的测试失败。

处理程序最小可复现代码（MWE） #

export async handler(event) {
  for (record of event.Records) {
    try {
      const {
        applicationId
      } = JSON.parse(JSON.parse(record.body).Message);

      const shouldHandleNotification = await isFeatureFlagOn(PARAMETER_STORE_ARN, FEATURE_FLAG);
      if (!shouldHandleNotification) {
        console.info(`Flag [SHOULD_HANDLE_NOTIFICATION] is off, skipping notification handling.`);
        return;
      }

      const applicationData = await getApplicationData(applicationId);
      if (applicationData.type == "human") {
        // handle application
      } else if (application.type == "viltrumite") {
        // handle application
      } else {
        throw new Error(`Cannot handle application type [${applicationData.type}]`);
      }
    } catch (e) {
      console.error(`Cannot handle record. Error message: ${e.message}`)
    }
  }
}

测试代码最小可复现示例 #

const mockIsFeatureFlagOn = jest.fn();
jest.mock("moduleIsFeatureFlagOn", () => ({
  isFeatureFlagOn: mockIsFeatureFlagOn,
}));

const mockGetApplicationData = jest.fn();
jest.mock("moduleGetApplicationData", () => ({
  getApplicationData: mockGetApplicationData,
}));

describe("SNSNotificationHandler", () => {
    beforeEach(() => {
      jest.clearAllMocks();
    });

  // 测试1
  it("特性标志关闭时不处理通知", async () => {
    mockIsFeatureFlagOn.mockResolvedValueOnce(false);
    mockGetApplicationData.mockResolvedValueOnce({
      type: "unknown"
    });

    await handler(EVENT_WITH_APPLICATION_DATA);

    mockIsFeatureFlagOn.toHaveBeenCalledWith(PARAMETER_STORE_ARN, FEATURE_FLAG);
    mockGetApplicationData.not.toHaveBeenCalled();
  });

  // 测试2
  it("处理viltrumite类型应用", async () => {
    mockIsFeatureFlagOn.mockResolvedValueOnce(true);
    mockGetApplicationData.mockResolvedValueOnce({
      type: "viltrumite"
    });

    await handler(EVENT_WITH_APPLICATION_DATA);

    mockIsFeatureFlagOn.toHaveBeenCalledWith(PARAMETER_STORE_ARN, FEATURE_FLAG);
    mockGetApplicationData.toHaveBeenCalled();
  });
}

测试2失败，因为mockGetApplicationData的mock实现未在测试1后清除，残留到测试2中返回{ type: "unknown" }而非预期的{ type: "viltrumite" }。测试1中mockGetApplicationData从未被调用，即使使用jest.clearAllMocks()，其实现仍会残留。我可以手动清除该mock的实现解决问题，但想了解背后原因：

已知jest.clearAllMocks设计上不会移除mock实现，但疑惑为何测试1中设置的、未被执行的mockResolvedValueOnce一次性实现会渗透到测试2中？未执行的一次性实现不应局限于当前测试，让mock回到jest.fn()的初始状态吗？

注：mockFn.mockResolvedValueOnce(value)是jest.fn().mockImplementationOnce(() => Promise.resolve(value))的简写，根据Jest文档：当用.mockImplementationOnce()定义的实现耗尽后，会执行jest.fn(() => defaultValue)或.mockImplementation(() => defaultValue)设置的默认实现。

内容的提问来源于stack exchange，提问作者uzluisf