Angular2 testing a module with an EventEmitter subscription in ngOnInit error

I am having trouble writing a testing module for an Angular2 component I have created. The component in question subscribes to another service's EventEmitter in it's ngOnInit method. The component is then subscribed to this EventEmitter and listens for changes. Here is the component in question:

import { Component } from "@angular/core";
import { Product } from "../../../classes/Product";
import { ProductService } from "../../../services/product.service";
import { ConfigObject } from "../../../ConfigObject";
import { productHelper } from "../../../helpers/productHelper";


@Component({
    selector: 'product-component',
    templateUrl: '/app/views/catalog/products/product-dashboard.html',
    moduleId: module.id
})

export class ProductComponent {
    globals = ConfigObject;
    products: Product[] = [];
    productsLoaded = false;

    productPayload = {
        order           : 'asc',
        order_by        : 'title',
        category_id     : 0,
        resize          : true,
        imgHeight       : 200,
        imgWidth        : 200,
        active          : 1,
        searchTerm      : '',
        manufacturer    : null
    };

    constructor(
        private _productService: ProductService
    ) {

    }

    getProducts(filters) {
        this.productsLoaded = false;

        this._productService.getProducts(filters)
            .subscribe(
                products => { this.products = productHelper.processImagesAndDownloads(products)},
                ()       => { },
                ()       => { this.productsLoaded = true }
        );
    }

    ngOnInit() {
        this._productService.emitter.subscribe(
            (products) => {
                this.products = productHelper.processImagesAndDownloads(products);
            },
            ()       => { },
            ()       => { }
        );

        this.getProducts({});
    }

}

As you can see, using the ngOnInit method the _productService.emitter EventEmitter is subscribed to.

I have attempted to use the spyOn method to mock this event emitter but with no success. I cannot seem to get this component testing correctly. Can anyone see what the problem is here:

import { ProductService } from "../../../../services/product.service";
import { TestBed, ComponentFixture, async } from "@angular/core/testing";
import { ProductComponent } from "../../../../components/catalog/products/ProductComponent";
import { HttpModule } from "@angular/http";
import { DebugElement, CUSTOM_ELEMENTS_SCHEMA } from "@angular/core";

let MockProductService = {
    emitter: () => {}
};

let comp:    ProductComponent;
let fixture: ComponentFixture<ProductComponent>;
let de:      DebugElement;
let el:      HTMLElement;

describe('Component: Product Component', () => {
    beforeEach(() => {
        TestBed.configureTestingModule({
            declarations: [
                ProductComponent
            ],
            providers: [
                {
                    provide: ProductService, useValue: MockProductService
                }
            ],
            imports: [
                HttpModule
            ],
            schemas: [CUSTOM_ELEMENTS_SCHEMA]
        });
    });

    it('Should check that products are loaded in the template', async(() => {

        TestBed.compileComponents()
            .then(() => {

                fixture = TestBed.createComponent(ProductComponent);
                comp = fixture.componentInstance;

                spyOn(MockProductService, 'emitter').and.returnValue({
                    subscribe: () => {}
                });
                comp.ngOnInit();

                expect(MockProductService.emitter).toHaveBeenCalled();
        });
    }));

});

The error I receive is:

Failed: Uncaught (in promise): TypeError: this._productService.emitter.subscribe is not a function