ReferenceError: service is not defined

I tried to test service, http post, like this code below.

I follow this post for my testing, but I have a error.

My service code:

  public CreateProduct(newProd: Product): Observable<boolean> {
    .....
    let body = newProd.generateUrlencodedParameters(this.currentuser().token);
    return this.http.post(API.getUrl(Api.URLS.CreateProduct), body, {
      headers: headers
    })
      .map((response: Response) => {
        let res = response.json();

        if (res.StatusCode === 0) {
          return true;
        }
    }

My class Product:

export class Product{
    id: number;
    prod_number: String;
    prod_name: string;

    constructor(obj: any) {
        this.id= obj.id;
        this.prod_number= obj.prod_number;
        this.prod_name= obj.prod_name;
    }
    public generateUrlencodedParameters(token: string, id?: number): string 
   {
        let urlSearchParams = new URLSearchParams();
        urlSearchParams.append('prod_number', this.prod_number.toString());
        urlSearchParams.append('prod_name', this.prod_name.toString());
        urlSearchParams.append('token', token);
        return urlSearchParams.toString();
    }
}

I tried this code, to testing my service code:

describe('Create Product ', () => {
    let trackerFormService: ProductService,
      mockService = {
        createProduct: jasmine.createSpy('createProduct').and.returnValue(Observable.of('your session object mock goes here'))
      };
        beforeEach(() => {
        TestBed.configureTestingModule({
          imports: [HttpModule],
          providers: [{
            provide: ProductService,
            useValue: mockService
          }] }); });

      beforeEach(inject([ProductService], (trackerFormService) => {
        service = trackerFormService;
      }));
      describe('createProduct', () => {
        it('add session ', () => {
          let fakeResponse = null;
          service.CreateProduct().subscribe((value) => {
            fakeResponse = value;
          }); }); });});

The result is:

ReferenceError: service is not defined

Please, can you suggest me any idea, how to solve this issue, or any example for testing service post.

Thnx.