[ ] Regression (a behavior that used to work and stopped working in a new release)
[X] Bug report  
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question

[example.service.spec.ts]

import { HttpClientTestingModule, HttpTestingController } from '@angular/common/http/testing';
import { Injector } from '@angular/core';
import { async, TestBed } from '@angular/core/testing';
import { ExampleService } from './example.service';

fdescribe('Create a test suite for the Example Service', () => {
    let injector: Injector;
    let exampleService: ExampleService;
    let httpMock: HttpTestingController;

    beforeEach(() => {
        injector = TestBed.configureTestingModule({
            imports:
                [HttpClientTestingModule],
            providers:
                [ExampleService]
        });
        exampleService = injector.get(ExampleService);
        httpMock = injector.get(HttpTestingController);
    });

    afterEach(() => {
        httpMock.verify();
    });

    it('should not immediately connect to the server', () => {
        httpMock.expectNone({});
    });

    describe('when fetching all stuff', () => {
        it('should make a GET request', async(() => {
            exampleService.getStuff();

            let req = httpMock.expectOne(`./assets/mock/modules.json`);
            expect(req.request.method).toEqual('GET');
            req.flush([]);
        }));
    });
});

[example.service.ts]

import { HttpClient, HttpParams } from '@angular/common/http';
import { Injectable } from '@angular/core';

@Injectable()
export class ExampleService {

    constructor(private http: HttpClient) {
    }

    getStuff() {
        let params = new HttpParams().append('testparam', 'testvalue')
        return this.http.get('./assets/mock/modules.json', {params}).toPromise().then(value => {
            return value
        })
    }
}

Angular version: 4.4.4


Browser:
- [X] Chrome (desktop) version 61.0.3163.100
- [ ] Chrome (Android) version XX
- [ ] Chrome (iOS) version XX
- [ ] Firefox version XX
- [ ] Safari (desktop) version XX
- [ ] Safari (iOS) version XX
- [ ] IE version XX
- [ ] Edge version XX
 
For Tooling issues:
- Node version: V8.4.0  
- Platform: Windows  

Others: