Angular2 Inject ElementRef in unit test

Question

I am trying to test a component that receives a reference to ElementRef through DI.

import { Component, OnInit, ElementRef } from '@angular/core';

@Component({
  selector: 'cp',
  templateUrl: '...',
  styleUrls: ['...']
})
export class MyComponent implements OnInit {

  constructor(private elementRef: ElementRef) {
    //stuffs
  }

  ngAfterViewInit() {
    // things
  }

  ngOnInit() {
  }
}

and the test:

import {
  beforeEach,
  beforeEachProviders,
  describe,
  expect,
  it,
  inject,
} from '@angular/core/testing';
import { ComponentFixture, TestComponentBuilder } from '@angular/compiler/testing';
import { Component, Renderer, ElementRef } from '@angular/core';
import { By } from '@angular/platform-browser';

describe('Component: My', () => {
  let builder: TestComponentBuilder;

  beforeEachProviders(() => [MyComponent]);
  beforeEach(inject([TestComponentBuilder], function (tcb: TestComponentBuilder) {
    builder = tcb;
  }));

  it('should inject the component', inject([MyComponent],
      (component: MyComponent) => {
    expect(component).toBeTruthy();
  }));

  it('should create the component', inject([], () => {
    return builder.createAsync(MyComponentTestController)
      .then((fixture: ComponentFixture<any>) => {
        let query = fixture.debugElement.query(By.directive(MyComponent));
        expect(query).toBeTruthy();
        expect(query.componentInstance).toBeTruthy();
      });
  }));
});

@Component({
  selector: 'test',
  template: `
    <cp></cp>
  `,
  directives: [MyComponent]
})
class MyTestController {
}

Both the component and the test blueprint have been generated by Angular-cli. Now, I can't figure out which provider, if any, I should add in the beforeEachProviders for the injection of ElementRef to be successful. When I run ng test I got Error: No provider for ElementRef! (MyComponent -> ElementRef).

Answer 1

To inject an ElementRef:

1. Create a mock

class MockElementRef implements ElementRef {
  nativeElement = {};
}

2. Provide the mock to the component under test

beforeEachProviders(() => [Component, provide(ElementRef, { useValue: new MockElementRef() })]);

EDIT: This was working on rc4. Final release introduced breaking changes and invalidates this answer.

Answer 2

On Angular 2.2.3:

export class MockElementRef extends ElementRef {}

Then in the test:

beforeEach(async(() => {
  TestBed.configureTestingModule({
    providers: [
      //more providers
      { provide: ElementRef, useClass: MockElementRef }
    ]
  }).compileComponents();
}));

Answer 3

I encounter Can't resolve all parameters for ElementRef: (?) Error using the mock from @gilad-s in angular 2.4

Modified the mock class to:

export class MockElementRef extends ElementRef {
  constructor() { super(null); }
}

resolves the test error.

Reading from the angular source code here: https://github.com/angular/angular/blob/master/packages/core/testing/src/component_fixture.ts#L17-L60 the elementRef of the fixture is not created from the mock injection. And in normal development, we do not explicitly provide ElementRef when injecting to a component. I think TestBed should allow the same behaviour.

Answer 4

A good way is to use spyOn and spyOnProperty to instant mock the methods and properties as needed. spyOnProperty expects 3 properties and you need to pass get or set as third property. spyOn works with class and method and returns required value.

Example

const div = fixture.debugElement.query(By.css('.ellipsis-overflow'));
// now mock properties
spyOnProperty(div.nativeElement, 'clientWidth', 'get').and.returnValue(1400);
spyOnProperty(div.nativeElement, 'scrollWidth', 'get').and.returnValue(2400);

Here I am setting the get of clientWidth of div.nativeElement object.