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
});

Doing a test host component is a way to do it but I understand it can be too much work.

The ngOnInit of a component gets called on the first fixture.detectChanges() after TestBed.createComponent(...).

So to make sure it is populated in the ngOnInit, set it before the first fixture.detectChanges().

Example:

fixture = TestBed.createComponent(BannerComponent);
component = fixture.componentInstance;
component.inputproperty = value; // set the value here
fixture.detectChanges(); // first fixture.detectChanges call after createComponent will call ngOnInit

I assume all of that is in a beforeEach and if you want different values for inputproperty, you have to get creative with describes and beforeEach.

For instance:

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

  beforeEach(async(() => {
    TestBed.configureTestingModule({declarations: [BannerComponent]}).compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(BannerComponent);
    component = fixture.componentInstance;
  });

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

  describe('inputproperty is blahBlah', () => {
   beforeEach(() => {
     component.inputproperty = 'blahBlah';
     fixture.detectChanges();
   });

   it('should do xyz if inputProperty is blahBlah', () => {
     // test when inputproperty is blahBlah
   });
  });

  describe('inputproperty is abc', () => {
   beforeEach(() => {
     component.inputproperty = 'abc';
     fixture.detectChanges();
   });

   it('should do xyz if inputProperty is abc', () => {
     // test when inputproperty is abc
   });
  });
});

Make sure to assign the required input before getting the component instance from the fixture

In your code:

fixture.componentRef.setInput('required', 'foo');
component = fixture.componentInstance;

Adjust your code as follows

beforeEach(
    waitForAsync(() => {
      TestBed.configureTestingModule({
        declarations: [ChildComponent],
        imports: [RouterTestingModule],
      }).compileComponents();
      fixture = TestBed.createComponent(ChildComponent);
      component = fixture.componentInstance;
      component.links = linksMock; // put this here
      fixture.detectChanges();
      class = new ChildTemplate();
    })
  );

Note ngOnInit is being called before your "it" block runs, hence the problem. I believe ngOnInit is called the very first time you call fixture.detectChanges() which you are calling in your beforeEach block.

the following works:

Include this import:

import { of } from 'rxjs';

Change the beforeEach block for the file to:

beforeEach(() => {
  fixture = TestBed.createComponent(BugsTableComponent);
  component = fixture.componentInstance;

  // needed because ngAfterViewInit gets called and if there isn't an observable to subscribe to it will fail
  component.bugsDataService = of(null);

  fixture.detectChanges();
});

Write a test:

it('Should assign the input value to bugsdata', () => {
  // Arrange
  component.bugsData = {}; // to make sure it's empty at the start
  const resultFromService = {hello: 'world'};
  component.bugsDataService = of(resultFromService); // this creates an observable from resultFromService

  // Act
  component.ngAfterViewInit();

  // Assert
  expect(component.bugsData).toEqual(resultFromService);
});

Some notes:

• I've noticed is that your component has a ngAfterViewInit but the class does not implement it. If you're not using ngOnInit then replace it in the class declaration with ngAfterViewInit and update the imports.
• If you don't want to do the change I suggested in the beforeEach block you can move the subscribe line from ngAfterViewInit to a separate method that is called by ngAfterViewInit. However, you'll then need to spy on it so it doesn't actually get called.