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A Jasmine helper for creating mocked classes
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Jasmine Mock Factory

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A Jasmine test util that uses a TypeScript class or an instance of a class to create a mock instance of that class.

Quick Start

import { SomeClass } from 'some-library';
import { MockFactory} from 'jasmine-mock-factory';

it('should pass', () => {
    const mockInstance = MockFactory.create(SomeClass);

    /* arrange */

    /* act */
    mockInstance.doSomething();  // returns 'awesome!'

    /* assert */

Quick reference

  /* create a mock from a class*/
  const mockInstance1 = MockFactory.create(RealClass);

  /* create a mock from an instance*/
  const mockInstance2 = MockFactory.create(realInstance);

  /* access a function spy */
  const spy1 = mockInstance._spy.functionName._func

  /* access a getter spy */
  const spy2 = mockInstance._spy.propertyName._get

  /* access a setter spy */
  const spy3 = mockInstance._spy.propertyName._set


  • This util is built with and for Jasmine test framework. Basic understanding of Jasmine is assumed.
  • This util requires ES6 Proxy.



npm install jasmine-mock-factory --save-dev


Import the library with ES6 Module Syntax:

import { MockFactory } from 'jasmine-mock-factory'

Creating a mock

From a TypeScript class

class RealClass {
  // This is a typescript class


const mockInstance = MockFactory.create(RealClass);

From an instance of a class

const realInstance: RealInterface = new RealClass();


const mockInstance = MockFactory.create(realInstance);

From window objects

/* make sure you have included dom types from the TypeScript library */
const mockWindow  = MockFactory.create(window);
const mockDocument = MockFactory.create(document);
const mockLocation = MockFactory.create(location);

Using a mock

  • MockFactory.create() will return an object with the same interface as the real object. You can invoke functions and access properties on this object.
  • In addition, the mock object provides a _spy facade, where you can access and config spies on functions and properties.
  const mockInstance = MockFactory.create(location);
  mockInstance.reload(); // use it as if it were the real window.location
  let temp =; // use it as if it were the real
  mockInstance.hash = 'myHash'; // use it as if it were the real window.hash
  mockInstance._spy.reload._func; // returns the spy behind location.reload; // returns the spy behind the getter for
  mockInstance._spy.hash._set; // returns the spy behind the setter for location.hash

Invoking functions

  • All functions will have a jasmine.Spy as the initial value. The spy cannot be overwritten and returns undefined by default.
  • To access protected and private functions, cast the mockInstance as any or use bracket notation.
  mockInstance.publicFunction(42); // the spy behind it is invoked with 42

  (mockInstance as any).privateFunction(42);
  mockInstance['privateFunction'](42); // equivalent

Spying/stubbing functions

  • You can change return values of functions or assert their calls by accessing them directly or through the _spy facade.
  • Access a function spy on mockInstance._spy.functionName._func.
  /* stubbing a public function */
  (mockInstance.publicFunction as jasmine.Spy).and.returnValue(42); // equivalent, but not recommented because it requires casting

  /* stubbing a private function */
  ((mockInstance as any).privateFunction as jasmine.Spy).and.returnValue(42); // equivalent, but not recommented because it requires casting twice

Accessing properties

  • All properties have undefined as the initial value. The value can be overwritten with anything.
  • You have read and write access to any property, even if they were readonly in the real object.
  • To read or write a protected or private property, cast the mockInstance as any or use bracket notation.
  • To write a readonly property, cast the mockInstance as any. The bracket notation won't work.
  • By default, modification to the properties will persist, even if a getter or setter exists in the real object.
  /* persist modification */
  mockInstance.publicProperty = 42;
  let temp = mockInstance.publicProperty; // temp = 42;

  /* access readonly property */
  mockInstance.readonlyProperty = 42; // typescript compiler error
  (mockInstance as any).readonlyProperty = 42; // no problem
  mockInstance['readonlyProperty'] = 42; // typescript compiler error

  /* access private property */
  (mockInstance as any).privateProperty = 'foo';
  mockInstance['privateProperty'] = 'foo'; // equivalent

Spying/stubbing getters and setters

  • All properties have spies on the getter and setter, even if the getter and setter don't exist in the real object.
  • Access a getter spy on mockInstance._spy.propertyName._get.
  • Access a setter spy on mockInstance._spy.propertyName._set.
  • NOTE: modification to the properties will not persist after getter or setter spies are customized
  • NOTE: expect(mockInstance.someProperty).toBe(...) will trigger mockInstance._spy.someProperty._get. Design the sequence of your assertions carefully to avoid shooting yourself in the foot.
  /* assert getter calls */
  let temp = mockInstance.publicProperty;

  /* assert setter calls on a public property */
  mockInstance.publicProperty = 42;

  /* customize setter */
  expect(mockInstance.publicProperty).toBe(42); // pass. setter hasn't been customized
  mockInstance._spy.publicProperty._set.and.callFake(() => { /* noop */});
  mockInstance.publicProperty = 100;
  expect(mockInstance.publicProperty).toBe(100); // fail. expect 42 to be 100. setter was customized

  /* assert setter calls on a private property */
  mockInstance['privateProperty'] = 42;

  /* customize getter */
  expect(mockInstance['privateProperty']).toBe(42); // pass. getter hasn't been customized
  mockInstance['privateProperty'] = 42;
  expect(mockInstance['privateProperty']).toBe(42); // fail, expect 100 to be 42. getter was customzied


  • npm install to install dev dependencies
  • npm run build to build the library
  • npm run test to test the library
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