在 Typescript Jest 中模擬導出 class

Question

嗨，我編寫了以下代碼來從 Azure Blob 存儲中獲取 Blob。

import { BlobServiceClient, ContainerClient, ServiceFindBlobsByTagsSegmentResponse } from '@azure/storage-blob';
import { GetBlobPageInput, GetBlobPageOutput, PutBlobItemsInput, GetBlobItem } from './interfaces/blob.service.interface';

export const getBlobsPage = async<T>(input: GetBlobPageInput) => {
  const blobServiceClient = BlobServiceClient.fromConnectionString(input.blobConnectionString);

  const iterator = blobServiceClient
  .findBlobsByTags(input.condition)
  .byPage({ maxPageSize: input.pageSize });

  return getNextPage<T>({
    iterator,
    blobServiceClient,
    blobContainer: input.blobContainer,
  });
};
[...]

我正在嘗試為它編寫一個單元測試，但是當我嘗試從 @azure/storage-blob 模擬 BlobServiceClient 時遇到了麻煩。 我這樣編寫示例測試和模擬：

import { getBlobsPage } from './../../services/blob.service';

const fromConnectionStringMock = jest.fn();
jest.mock('@azure/storage-blob', () => ({
  BlobServiceClient: jest.fn().mockImplementation(() => ({
    fromConnectionString: fromConnectionStringMock,
  })),
}));

describe('BLOB service tests', () => {
  beforeEach(() => {
    jest.clearAllMocks();
  });

  it('should fetch first page and return function to get next', async () => {
    const input = {
      blobConnectionString: 'testConnectionString',
      blobContainer: 'testContainer',
      condition: "ATTRIBUTE = 'test'",
      pageSize: 1,
    };

    const result = await getBlobsPage(input);

    expect(fromConnectionStringMock).toHaveBeenCalledTimes(1);
  });
});

但是當我嘗試運行測試時，我得到：

 TypeError: storage_blob_1.BlobServiceClient.fromConnectionString is not a function

      24 | 
      25 | export const getBlobsPage = async<T>(input: GetBlobPageInput) => {
    > 26 |   const blobServiceClient = BlobServiceClient.fromConnectionString(input.blobConnectionString);
         |                                               ^
      27 | 
      28 |   const iterator = blobServiceClient
      29 |   .findBlobsByTags(input.condition)

      at nhsdIntegration/services/blob.service.ts:26:47
      at nhsdIntegration/services/blob.service.ts:1854:40
      at Object.<anonymous>.__awaiter (nhsdIntegration/services/blob.service.ts:1797:10)
      at Object.getBlobsPage (nhsdIntegration/services/blob.service.ts:25:65)
      at tests/services/blob.service.test.ts:27:26
      at tests/services/blob.service.test.ts:8:71

關於如何正確實現 azure 模塊的模擬的任何提示？

我在 StackOverflow 上嘗試了幾個不同的答案，並查看了 web 上的文章（例如： https://dev.to/codedivoire/how-to-mock-an-imported-typescript-class-with-jest-2g7j ）。 他們中的大多數都表明這是正確的解決方案，所以我想我在這里遺漏了一些小東西，但無法弄清楚。

Answer 1

導出的BlobServiceClient應該是文字 object 但您現在是 mocking 為 function 這是問題所在。

因此，您可能需要簡單地模擬返回文字 object。 另一個問題是從模擬 scope 外部訪問 var fromConnectionStringMock會導致另一個問題。

所以這可能是正確的模擬：

jest.mock('@azure/storage-blob', () => ({
  ...jest.requireActual('@azure/storage-blob'), // keep other props as they are
  BlobServiceClient: {
    fromConnectionString: jest.fn().mockReturnValue({
      findBlobsByTags: jest.fn().mockReturnValue({
        byPage: jest.fn(),
      }),
    }),
  },
}));