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.