Jasmine Mock Factory

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 */
    mockInstance._spy.doSomething._func.and.returnValue('awesome!');
 
    /* act */
    mockInstance.doSomething();  // returns 'awesome!'
 
    /* assert */
    expect(mockInstance.doSomething).toHaveBeenCalled();
}

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

Prerequisite

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

Usage

Install

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

Import

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 = mockInstance.search; // use it as if it were the real window.search
  mockInstance.hash = 'myHash'; // use it as if it were the real window.hash
  mockInstance._spy.reload._func; // returns the spy behind location.reload
  mockInstance._spy.search._get; // returns the spy behind the getter for location.search
  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._spy.publicFunction._func.and.returnValue(42);
  (mockInstance.publicFunction as jasmine.Spy).and.returnValue(42); // equivalent, but not recommented because it requires casting
 
  /* stubbing a private function */
  mockInstance._spy.privateFunction._func.and.returnValue(42);
  ((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;
  expect(mockInstance._spy.publicProperty._get).toHaveBeenCalled();
 
  /* assert setter calls on a public property */
  mockInstance.publicProperty = 42;
  expect(mockInstance._spy.publicProperty._set).toHaveBeenCalledWith(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;
  expect(mockInstance._spy.privateProperty._set).toHaveBeenCalledWith(42);
 
  /* customize getter */
  expect(mockInstance['privateProperty']).toBe(42); // pass. getter hasn't been customized
  mockInstance._spy.privateProperty._get.and.returnValue(100);
  mockInstance['privateProperty'] = 42;
  expect(mockInstance['privateProperty']).toBe(42); // fail, expect 100 to be 42. getter was customzied

Develope

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