Mock exported class in Typescript Jest - node.js

Question

Hi i wrote following code to fetch blobs from Azure Blob Storage.
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,
});
};
[...]
I am trying to write a unit test for it, but i have trouble when i try to mock BlobServiceClient from #azure/storage-blob. I wrote sample test and mock as this:
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);
});
});
But when i try to run test i am getting:
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
Any tips on how should I properly implement mock for azure module?
I've tried following several diffrent answers on StackOverflow and looked through articles on web (like: https://dev.to/codedivoire/how-to-mock-an-imported-typescript-class-with-jest-2g7j). And most of them show that this is the proper solution, so i guess i am missing some small thing here but can't figure it out.

Answer 1

The exported BlobServiceClient is supposed to be a literal object but you're now mocking as function which is the issue.
So you might need to simply mock returning a literal object. Another issue is to access a var fromConnectionStringMock from outside of the mock scope would end up with another issue.
So here's possibly the right mock:
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(),
}),
}),
},
}));