Angular2 unit test with @Input()

I've got a component that uses the @Input() annotation on an instance variable and I'm trying to write my unit test for the openProductPage() method, but I'm a little lost at how I setup my unit test. I could make that instance variable public, but I don't think I should have to resort to that.

How do I setup my Jasmine test so that a mocked product is injected (provided?) and I can test the openProductPage() method?

My component:

import {Component, Input} from "angular2/core";
import {Router} from "angular2/router";

import {Product} from "../models/Product";

@Component({
    selector: "product-thumbnail",
    templateUrl: "app/components/product-thumbnail/product-thumbnail.html"
})

export class ProductThumbnail {
    @Input() private product: Product;


    constructor(private router: Router) {
    }

    public openProductPage() {
        let id: string = this.product.id;
        this.router.navigate([“ProductPage”, {id: id}]);
    }
}

this is from official documentation https://angular.io/docs/ts/latest/guide/testing.html#!#component-fixture. So you can create new input object expectedHero and pass it to the component comp.hero = expectedHero

Also make sure to call fixture.detectChanges(); last, otherwise property will not be bound to component.

Working Example

// async beforeEach
beforeEach( async(() => {
    TestBed.configureTestingModule({
        declarations: [ DashboardHeroComponent ],
    })
    .compileComponents(); // compile template and css
}));

// synchronous beforeEach
beforeEach(() => {
    fixture = TestBed.createComponent(DashboardHeroComponent);
    comp    = fixture.componentInstance;
    heroEl  = fixture.debugElement.query(By.css('.hero')); // find hero element

    // pretend that it was wired to something that supplied a hero
    expectedHero = new Hero(42, 'Test Name');
    comp.hero = expectedHero;
    fixture.detectChanges(); // trigger initial data binding
});

If you use TestBed.configureTestingModule to compile your test component, here's another approach. It's basically the same as the accepted answer, but may be more similar to how angular-cli generates the specs. FWIW.

import { Component, CUSTOM_ELEMENTS_SCHEMA } from '@angular/core';
import { async, ComponentFixture, TestBed } from '@angular/core/testing';
import { DebugElement } from '@angular/core';

describe('ProductThumbnail', () => {
  let component: ProductThumbnail;
  let fixture: ComponentFixture<TestComponentWrapper>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ 
        TestComponentWrapper,
        ProductThumbnail
      ],
      schemas: [CUSTOM_ELEMENTS_SCHEMA]
    })
    .compileComponents();

    fixture = TestBed.createComponent(TestComponentWrapper);
    component = fixture.debugElement.children[0].componentInstance;
    fixture.detectChanges();
  });

  it('should create', () => {
    expect(component).toBeTruthy();
  });
});

@Component({
  selector: 'test-component-wrapper',
  template: '<product-thumbnail [product]="product"></product-thumbnail>'
})
class TestComponentWrapper {
  product = new Product()
}

You need to set the product value on the component instance after it has been loaded within your test.

As a sample here is a simple component within an input that you can use as a foundation for your use case:

@Component({
  selector: 'dropdown',
  directives: [NgClass],
  template: `
    <div [ngClass]="{open: open}">
    </div>
  `,
})
export class DropdownComponent {
  @Input('open') open: boolean = false;

  ngOnChanges() {
    console.log(this.open);
  }
}

And the corresponding test:

it('should open', injectAsync([TestComponentBuilder], (tcb: TestComponentBuilder) => {
  return tcb.createAsync(DropdownComponent)
  .then(fixture => {
    let el = fixture.nativeElement;
    let comp: DropdownComponent = fixture.componentInstance;

    expect(el.className).toEqual('');

    // Update the input
    comp.open = true; // <-----------

    // Apply
    fixture.detectChanges(); // <-----------

    var div = fixture.nativeElement.querySelector('div');
    // Test elements that depend on the input
    expect(div.className).toEqual('open');
  });
}));

See this plunkr as a sample: https://plnkr.co/edit/YAVD4s?p=preview.

I usually do something like:

describe('ProductThumbnail', ()=> {
  it('should work',
    injectAsync([ TestComponentBuilder ], (tcb: TestComponentBuilder) => {
      return tcb.createAsync(TestCmpWrapper).then(rootCmp => {
        let cmpInstance: ProductThumbnail =  
               <ProductThumbnail>rootCmp.debugElement.children[ 0 ].componentInstance;
      
        expect(cmpInstance.openProductPage()).toBe(/* whatever */)
      });
  }));
}

@Component({
 selector  : 'test-cmp',
 template  : '<product-thumbnail [product]="mockProduct"></product-thumbnail>',
 directives: [ ProductThumbnail ]
})
class TestCmpWrapper { 
    mockProduct = new Product(); //mock your input 
}

Note that product and any other fields on the ProductThumbnail class can be private with this approach (which is the main reason I prefer it over Thierry's approach, despite the fact that it's a little more verbose).