Angular 2 / 4 - How to test Directive @Input values?

Question

So I have a Directive that takes an input:

@Directive({
    selector: '[my-directive]'
})
export class MyDirective {

    @Input('some-input')
    public someInput: string;
}

As you can see, the input should be a string value. Now, I want to write a test for this Directive, and I want to test if the input satisfies the string type:

describe('MyDirective', () => {

    let fixture: ComponentFixture<DummyComponent>;
    let dummy: DummyComponent;
    let directive: DebugElement;

    beforeEach(async(() => {

        TestBed
            .configureTestingModule({
                imports: [
                    MyModule.forRoot()
                ],
                declarations: [
                    DummyComponent
                ]
            })
            .compileComponents();

        fixture = TestBed.createComponent(DummyComponent);
        dummy = fixture.componentInstance;
        directive = fixture.debugElement.query(By.directive(MyDirective));

        fixture.detectChanges();
    }));

    it('should satisfy only a string input and error on other inputs', () => {
        // How to test?
    });
});

@Component({
    selector: 'dummy',
    template: `
        <div my-directive [some-input]="'just-a-string-value'"></div>
    `
})
export class DummyComponent implements OnInit {
}

How can I test whether the @Input value(s) are of the proper type?

Answer 1

So it's a bit late but I came here searching for the same problem, so I'll post my solution. Here is what I did to test a directive inputs (or other properties) values :

describe('MyDirective', () => {

    let fixture: ComponentFixture<DummyComponent>;
    let dummy: DummyComponent;
    let directive: DebugElement;

    beforeEach(async(() => {

        TestBed
            .configureTestingModule({
                imports: [
                    MyModule.forRoot()
                ],
                declarations: [
                    DummyComponent
                ]
            })
            .compileComponents();

        fixture = TestBed.createComponent(DummyComponent);
        dummy = fixture.componentInstance;
        directive = fixture.debugElement.query(By.directive(MyDirective));

        fixture.detectChanges();
    }));

    it('should satisfy only a string input and error on other inputs', () => {
        
        // needed so template is processed, inputs are updated
        fixture.detectChanges();
        
        // since we declared a ViewChild on the directive, we can access
        // and test directive properties values
        expect(component.directive.someInput).toEqual('just-a-string-value');
        // to test the input type :
        expect(component.directive.someInput).toEqual(Jasmine.any(String));
        // I thought TypeScript would complain when providing a wrong type input to a directive, but no...so I guess I'll test the input type too !
    });
});

@Component({
    selector: 'dummy',
    template: `
        <div my-directive [some-input]="'just-a-string-value'"></div>
    `
})
export class DummyComponent implements OnInit {

  // add a reference to the directive in template
  // so in your component you can access : this.directive, this.directive.someInput
  ViewChild(MyDirective) directive: MyDirective;
}

So : modify your testing component to hold a reference on the directive instance, and then access the directive properties through component.directive.[property-name]. By the way if you provide defaults values for your directive properties (that can be overridden by providing a value in the template), you can test them before calling fixture.detectChanges().