jest-mock-proxy

jest-mock-proxy

Mock classes and objects with the power of proxies!

Creates a Proxy that will dynamically create spies when a property is accessed the first time. Every subsequent access will use the same spy. In combination with TypeScript this allows us to create a mock for any class/object without having to specify all its properties and methods.

tl;dr;

• The Proxy makes any property and method available on the mock at runtime.
• TypeScript limits access to properties and methods to the specified generic.

Install

Requires node 8+.

$ yarn add -D jest-mock-proxy

or

$ npm install -D jest-mock-proxy

Usage

Mock objects and instances

// service.ts
export class Service {
  foo() {
    console.log('hello');
  }
  bar(s: string) {
    return s;
  }
}

// some.test.ts
import { createMockProxy } from 'jest-mock-proxy';
import { service } from './service';

const mock = createMockProxy<typeof Service>();

mock.foo();

mock.bar.mockReturnValue('some string');
mock.bar('test'); // 'some string'

Example: Mock an elastic search client.

import { Client } from 'elasticsearch';
import { createMockProxy } from 'jest-mock-proxy';
import fixture from './__fixtures__/elastic-response.json';

// This is an imaginary service that depends on the elastic search client.
import createService from './createService';

const client = createMockProxy<Client>();
const service = createService(client);

beforeEach(() => {
  client.mockClear();
  client.search.mockResolvedValue(fixture);
});

test('use service to query', async () => {
  await service.query('https://example.com?q=hello');
  expect(client.search.mock.calls).toMatchSnapshot();
});

Mock a class and use jest's automock

When you need to mock a dependency via jest.mock, because you have no access to the module.

// query.ts
import { Pool, PoolConfig } from 'pg';

// 😨 This makes testing hard...
const pool = new Pool();

export const query = async (q: string, values?: any[]) => {
  // ...because how to mock this?
  const { rows } = pool.query(q, values);
  return rows;
};

// query.test.ts
import { Pool } from 'pg';
import { createProxyFromMock } from 'jest-mock-proxy';

import { query } from './query';

jest.mock('pg');
const mockedPool = createProxyFromMock(Pool);

test('you can now mock the pool.query', async () => {
  // Use mockedPool so you get good type inference from TS
  mockedPool.query.mockResolvedValue({ rows: [{ id: 1, data: 'data' }] });

  await query('SELECT * FROM table1'); // returns `[{ id: 1, data: 'data' }]`
});

Changelog

3.1.2 (2022-05-19)

Tooling

• Fix build (fe802b8)

[object Object]## 3.1.1 (2022-05-19)

Refactoring & Improvements

• Add option to name a mock (ca1f639)

Tooling

• Move to GH Actions (3f9258d)
• Naming is hard ... (ec61c25)

Documentation

• Fix typos in readme (2ae246b)
• Use action badge (2eaa05b)

Miscellaneous

• Name the mock functions (#3) (ab14878), closes [#3](https://github.com/sebald/jest-mock-proxy/issues/Name the mock functions (#3/

[object Object]# 3.0.0 (2019-03-22)

Features

• Introduce createProxyFromMock (#2) (cfdd310), closes [#2](https://github.com/sebald/jest-mock-proxy/issues/✨ Introduce createProxyFromMock (#2/

Tooling

• Add codecov (a2db790)
• Add husky ... (fa6bd7c)
• Exclude fixtures from coverage. (4321ffe)
• Setup changelog (c7c3d82)
• TSLint -> ESLint (65328cf)
• Configure yarn version message (519839a)
• No CI email on success (1ac59fe)
• Require jest v24+ (ef9dbfe)
• Update dependencies (859c6d3)

Documentation

• Add coverage badge (c854b77)
• Improve tldr (dc91464)
• Not a real project w/o badges! (b403119)

Miscellaneous

• Initial commit (f2e71a7)

[object Object]