jest-spy-object

Spies on all Object or Class methods using jest.spyOn.

Why?

If you're sick of writing jest.spyOn(Object, 'method') all the time.
And you want the following:

You need to spy on some or all methods of an Object or Class
You need to define mocks for some methods inside tests (mockImplementation or mockReturnValue)
You need each test to have fresh spies without calling mockRretore or mockReset on each spy
You don't want to manually add a spy for newly added methods

Installation

Install as a dev dependency of your project:

yarn add -D jest-spy-object

Or with npm

npm i -D jest-spy-object

Require

const spyObject = require('jest-spy-object');

Usage

Given a Class

class Counter {
  constructor() {
    this.value = 0;
  }

  incrementBy(val) {
    this.value = this.value + val;
  }

  increment() {
    this.incrementBy(1);
  }
}

Before

beforeEach(() => {
  // Make sure each test starts fresh (can be set in jest.config.js with `restoreMocks: true`)
  jest.restoreAllMocks();

  // Setup fresh spies
  jest.spyOn(Counter.prototype, 'incrementBy');
  jest.spyOn(Counter.prototype, 'increment');
});

After

const spyObject = require('jest-spy-object');

beforeEach(() => {
  // Make sure each test starts fresh (can be set in jest.config.js with `restoreMocks: true`)
  jest.restoreAllMocks();

  // Setup fresh spies
  spyObject(Counter);
});

Tests

describe('Counter', () => {
  it('should be able to spy on class methods and mock any of them easily', () => {
    const counter = new Counter();

    counter.incrementBy.mockImplementation(function() {
      this.value = this.value + 10;
    });

    counter.increment();

    expect(counter.increment).toHaveBeenCalled();
    expect(counter.incrementBy).toHaveBeenCalledWith(1);
    expect(counter.value).toBe(10);
  });
});

Other supported inputs

Function constructor

function Counter() {
  this.value = 0;
}

Counter.prototype.incrementBy = function incrementBy(val) {
  this.value = this.value + val;
};

Counter.prototype.increment = function increment() {
  this.incrementBy(1);
};

spyObject(Counter);
// or...
spyObject(Counter.prototype);

Plain Object

const counter = {
  value: 0,
  incrementBy(val) {
    this.value = this.value + val;
  },
  increment() {
    this.incrementBy(1);
  }
};

spyObject(counter);

Contributing

See the CONTRIBUTING document.

alexilyaev/jest-spy-object