Jest mock typescript dependency - node.js

Question

My index.ts file looks like this
import {IS3Client, S3Client} from './client/S3Client';
const s3: IS3Client = new S3Client();
export async function someFunc(event: any, context: any, callback: any) {
const x: string = await s3.getFile('a','b');
}
S3Client.ts looks like this
import * as AWS from 'aws-sdk';
export interface IS3Client {
getFile(bucketName: string, fileName: string): Promise<any>;
}
export class S3Client implements IS3Client {
private s3Client: AWS.S3;
constructor() {
this.s3Client = new AWS.S3();
}
public async getFile(bucketName: string, fileName: string): Promise<any> {
const params = {
Bucket: bucketName,
Key: fileName,
};
return (await this.s3Client.getObject(params).promise()).Body.toString();
}
}
Now I am interested to mock the getFile function to return what I want when I am testing index.ts
My test case looks like this
import {someFunc} from '../src/index';
import { S3Client } from '../src/client/S3Client';
describe("Test Suite", () => {
beforeAll(()=>{
jest.mock('../src/client/S3Client');
const mockedClient: jest.Mocked<S3Client> = new S3Client() as any;
mockedClient.getFile.mockImplementation(() => Promise.resolve('hello'));
});
it("testCase", () => {
const req = {
"key" : ["value"]
};
someFunc(req, null, null);
})
});
I am getting the following error :
TypeError: mockedClient.getFile.mockImplementation is not a function
Somehow this is looking much harder than I thought. Can someone suggest something, Thanks in advance ?
I added another class like this
import { SecretsManager } from 'aws-sdk';
export default class XUtils {
private secretsManager: SecretsManager;
constructor(secretsManager: SecretsManager) {
this.secretsManager = secretsManager;
}
public async getData(urlPrefix: string): Promise<any[]> {
return ['data'];
}
}
And my index.ts looks something like this :
import {IS3Client, S3Client} from './client/S3Client';
import XUtils from './utils/XUtils';
import { SecretsManager } from 'aws-sdk';
const s3: IS3Client = new S3Client();
const secretsManager: SecretsManager = new SecretsManager({ region: process.env.AWS_REGION });
const xUtils: XUtils = new XUtils(secretsManager)
export async function someFunc(event: any, context: any, callback: any) {
const x: string = await s3.getFile('a','b');
const y = await xUtils.getData(x);
}
Following from what you suggested, I modified my test case to something like this :
import {someFunc} from '../src/index';
import { S3Client } from '../src/client/S3Client';
import XUtils from '../utils/XUtils';
jest.mock('../src/client/S3Client', () => {
const mS3Client = { getFile: jest.fn() };
return { S3Client: jest.fn(() => mS3Client) };
});
jest.mock('../utils/XUtils', () => {
const mXUtils = { getData: jest.fn() };
return { XUtils: jest.fn(() => mXUtils) };
});
describe("Test Suite", () => {
beforeAll(()=>{
mockedClient = new S3Client() as any;
mockedClient.getFile.mockImplementation(() => Promise.resolve('url'));
mockedXUtils = new XUtils(null) as any;
mockedXUtils.getData.mockImplementation(() => Promise.resolve(['data']))
});
it("testCase", () => {
const req = {
"key" : ["value"]
};
someFunc(req, null, null);
})
});
I am getting error now as
TypeError: XUtils_1.default is not a constructor
What exactly is this problem ?

Answer 1

You can't use jest.mock in the function scope. It should be used in module scope.
You should use async/await for someFunc method in your test case.
E.g.
index.ts:
import { IS3Client, S3Client } from './s3client';
const s3: IS3Client = new S3Client();
export async function someFunc(event: any, context: any, callback: any) {
const x: string = await s3.getFile('a', 'b');
}
s3client.ts:
import * as AWS from 'aws-sdk';
export interface IS3Client {
getFile(bucketName: string, fileName: string): Promise<any>;
}
export class S3Client implements IS3Client {
private s3Client: AWS.S3;
constructor() {
this.s3Client = new AWS.S3();
}
public async getFile(bucketName: string, fileName: string): Promise<any> {
const params = {
Bucket: bucketName,
Key: fileName,
};
return (await this.s3Client.getObject(params).promise()).Body!.toString();
}
}
index.test.ts:
import { someFunc } from './';
import { S3Client } from './s3client';
jest.mock('./s3client', () => {
const mS3Client = { getFile: jest.fn() };
return { S3Client: jest.fn(() => mS3Client) };
});
describe('Test Suite', () => {
let mockedClient: jest.Mocked<S3Client>;
beforeAll(() => {
mockedClient = new S3Client() as any;
mockedClient.getFile.mockImplementation(() => Promise.resolve('hello'));
});
it('testCase', async () => {
const req = {
key: ['value'],
};
await someFunc(req, null, null);
expect(mockedClient.getFile).toBeCalledWith('a', 'b');
});
});
Unit test results with 100% coverage:
PASS stackoverflow/60445082/index.test.ts (8.548s)
Test Suite
✓ testCase (6ms)
----------|---------|----------|---------|---------|-------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------|---------|----------|---------|---------|-------------------
All files | 100 | 100 | 100 | 100 |
index.ts | 100 | 100 | 100 | 100 |
----------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 10.04s
source code: https://github.com/mrdulin/react-apollo-graphql-starter-kit/tree/master/stackoverflow/60445082