How to write unit test case for uploadFiles method using jest? - node.js

Question

i am trying to write unit test case for uploadFiles() method. This method returns function so i have to check toHaveBeenCalledWith('files', 5). I have updated my test case below, I don't know how to mock return function upload.array. can anyone tell me is that possible?
Method
uploadFiles = (
storage: StorageType,
validationFn: (request: Request, file: Express.Multer.File, cb: FileFilterCallback) => Promise<void>,
) => {
// fileSize - size of an individual file (1024 * 1024 * 1 = 1mb)
const upload = multer({
storage: this[storage](),
limits: { fileSize: 1024 * 1024 * FILE_SIZE },
fileFilter: this.fileUtil.fileValidation(validationFn),
});
return upload.array("files", 5); // maximum files allowed to upload in a single request
};
Test Case
describe('FileService', () => {
// fileValidation Test suite
describe('fileValidation', () => {
let callbackFn: jest.Mock<any, any>;
let validationFn: jest.Mock<any, any>;
beforeEach(() => {
callbackFn = jest.fn();
validationFn = jest.fn();
});
afterEach(() => {
callbackFn.mockClear();
validationFn.mockClear();
});
it('should call the file filter method with image file types when request body has type image', async () => {
// Preparing
const request = {
body: {
entity_no: 'AEZ001',
type: 'image',
category: 'Shipping',
},
};
const file = {
originalname: 'some-name.png',
mimetype: 'image/png',
};
// Executing
const func = fileService.uploadFiles(StorageType.DISK, validationFn);
await func(request as Request, file as any, callbackFn);
});
});
});

Answer 1

You can use jest.mock(moduleName, factory, options) to mock multer module.
E.g.
fileService.ts:
import multer from 'multer';
const FILE_SIZE = 1;
type FileFilterCallback = any;
export enum StorageType {
DISK = 'disk',
}
export class FileService {
fileUtil = {
fileValidation(fn) {
return fn;
},
};
disk() {
return multer.diskStorage({
destination: function (req, file, cb) {
cb(null, '/tmp/my-uploads');
},
filename: function (req, file, cb) {
cb(null, file.fieldname + '-' + Date.now());
},
});
}
uploadFiles = (
storage: StorageType,
validationFn: (request: Request, file: Express.Multer.File, cb: FileFilterCallback) => Promise<void>
) => {
const upload = multer({
storage: this[storage](),
limits: { fileSize: 1024 * 1024 * FILE_SIZE },
fileFilter: this.fileUtil.fileValidation(validationFn),
});
return upload.array('files', 5);
};
}
fileService.test.ts:
import { FileService, StorageType } from './fileService';
import multer from 'multer';
const mMulter = {
array: jest.fn(),
};
jest.mock('multer', () => {
const multer = jest.fn(() => mMulter);
const oMulter = jest.requireActual('multer');
for (let prop in oMulter) {
if (oMulter.hasOwnProperty(prop)) {
multer[prop] = oMulter[prop];
}
}
return multer;
});
describe('65317652', () => {
afterAll(() => {
jest.resetAllMocks();
});
let validationFn: jest.Mock<any, any>;
beforeEach(() => {
validationFn = jest.fn();
});
afterEach(() => {
validationFn.mockClear();
});
it('should pass', () => {
const fileService = new FileService();
fileService.uploadFiles(StorageType.DISK, validationFn);
expect(multer).toBeCalled();
expect(mMulter.array).toHaveBeenCalledWith('files', 5);
});
});
unit test result:
PASS examples/65317652/fileService.test.ts
65317652
✓ should pass (3 ms)
----------------|---------|----------|---------|---------|-------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------------|---------|----------|---------|---------|-------------------
All files | 84.62 | 100 | 71.43 | 84.62 |
fileService.ts | 84.62 | 100 | 71.43 | 84.62 | 19-22
----------------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 4.693 s