angular-unit-test-helper

Angular Unit Test Helper

Helper functions to help write unit tests in Angular using mocks and spies

Goal

Minimal feature set to bridge obvious gaps in jasmine's support of modern JavaScript features. Ideally, I'd like to be using an auto-mocking library, but they don't play well with Angular's TestBed and RxJS\BehaviorSubject.

Here's a great article about auto-mocking libraries: https://hackernoon.com/with-typescript-3-and-substitute-js-you-are-already-missing-out-when-mocking-or-faking-a3b3240c4607.

Install

Add the package to your Angular project with npm:

npm i -D angular-unit-test-helper

Example Projects

Check out my sample projects:

• https://github.com/duluca/local-weather-app
• https://github.com/duluca/lemon-mart

Features

autoSpyObj(classUnderTest: Function, spyProperties: string[] = [], observableStrategy = ObservablePropertyStrategy.Observable)

An extension of jasmine.createSpyObj with automatic discovery of functions and property getters given a Class, without requiring an instance of an object.

If you'd want to spy on a property without a getter, then you can simply pass in the property name like autoSpyObj(WeatherService, ['currentWeather$']).

Return value of autoSpyObj will be a true mock of the Class with spy-able methods and properties, making it easy to control and modify the return values of external dependencies during testing.

If property name ends with $ indicating that the property is an Observable, then you can specify an optional ObservablePropertyStrategy to prefer {}, new Observable() or new BehaviorSubject(null) default values for your mocked properties.

Usage

const weatherServiceSpy = autoSpyObj(WeatherService)

Alternate Usage

const weatherServiceSpy = autoSpyObj(
  WeatherService,
  ['currentWeather$'],
  ObservablePropertyStrategy.BehaviorSubject
)

autoSpyObj replaces the more verbose and difficult to maintain code, shown below:

jasmine.createSpyObj(WeatherService.name, [
  'getCurrentWeather',
  'getCurrentWeatherByCoords',
  'updateCurrentWeather',
])
addPropertyAsBehaviorSubject(weatherServiceSpy, 'currentWeather$')

addProperty(object: object, propertyName: string, valueToReturn: object)

When creating a mock object, add a property to that object with a property getter, so you can use a jasmine.spyOnProperty.

Usage

  weatherServiceMock = jasmine.createSpyObj('WeatherService', ['getCurrentWeather'])
  addPropertyAsBehaviorSubject(weatherServiceMock, 'currentWeather', null)
  ...
  spyOnProperty(weatherServiceMock, 'currentWeather$').and.returnValue({ temp = 72})

addPropertyAsBehaviorSubject(object: object, propertyName: string)

Convenience method to configure a property as a BehaviorSubject, so you can update its value before each test by calling .next on it.

Usage

  weatherServiceMock = jasmine.createSpyObj('WeatherService', ['getCurrentWeather'])
  addPropertyAsBehaviorSubject(weatherServiceMock, 'currentWeather$')
  ...
  weatherServiceMock.currentWeather$.next(fakeWeather)

createComponentMock(className: string, selectorName?: string, template = '')

Creates a mock class decorated with @Component, if not specified selector is inferred to be MyClassComponent -> app. Provides an option to override empty template.

Usage

TestBed.configureTestingModule({
      declarations: [ ..., createComponentMock('CurrentWeatherComponent')]
      ...
})

Note: Inferred selector in the above example is 'app-current-weather'.

Replaces boilerplate

@Component({
  selector: 'app-current-weather',
  template: '',
})
class MockCurrentWeatherComponent {}

injectOne<TDependency, TReturn>(dependency: Type<TDependency>): TReturn

Helper function to inject a dependency, like a service, into the TestBed with a typed return variable.

Usage

beforeEach(() => {
  weatherServiceMock = injectOne(WeatherService)
})

Replaces

beforeEach(() => {
  weatherServiceMock = TestBed.inject(WeatherService) as any
})

injectSpy<TDependency>(dependency: Type<TDependency>): jasmine.SpyObj<TDependency>

Helper function to inject a dependency, like services, into the TestBed and assign it to the mocked SpyObj.

Usage

beforeEach(() => {
  weatherServiceMock = injectSpy(WeatherService)
})

Replaces

beforeEach(() => {
  weatherServiceMock = TestBed.inject(WeatherService) as any
})

getAllFunctions(prototype: any, props?: (string | number | symbol)[])

Helper function that return all functions in a given Class using reflection, so you don't have to provide an instance of the object.

getAllProperties(prototype: any, props?: (string | number | symbol)[])

Helper function that return all property getters in a given Class using reflection, so you don't have to provide an instance of the object.

Contributing

• Send PR, will accept
• To setup the project, run npm install
• Test against the example project listed below using npm link
• To publish the project, run npm version major|minor|patch

  Read more about that setup by Isaac Schlueter here