Angular 6 – NullInjectorError: No provider for HttpClient in unit tests
If you don’t import HttpClientModule (or HttpClientTestingModule) there, HttpClient won’t work because Angular doesn’t know about it. It doesn’t matter that you added HttpClientModule to, say, AppModule. It needs to be in TestBed.configureTestingModule.

import { TestBed } from '@angular/core/testing';
import { HttpClientTestingModule, HttpTestingController } from '@angular/common/http/testing';
import {HttpClientModule} from '@angular/common/http';

describe('myService', () => {
.
.
.
});