Unable to load HttpClient in Service of Component

Let's suppose this structure:

```typescript
@Component({
selector: 'app-component',
templateUrl: './component.component.html',
styleUrls: ['./component.component.scss']
})
export class Component implements OnInit {

constructor(private service: CustomService) { }

ngOnInit(): void {
this.service.method().subscribe(...);
}

}
```
```typescript
@Injectable({
providedIn: 'root'
})
export class CustomService extends AbstractService {

private readonly URL: string;

constructor(private http: HttpClient) {
super('CustomService');

this.URL = this.getRelativeServiceURL('/suburl');
}

public method(): Observable {
return this.http.get(this.URL)
.pipe(map(value => {
return value.filtered;
}));
}
}
```

I wrote this test:
```typescript
it('should create', () => {
initEnv(Component, {
providers: [ CustomService ], imports: [ HttpClientTestingModule ]});
mount(Component);

cy.get(selector.empty.header)
.should('be.visible');
});
```

But I still get the error: "Can't resolve all parameters for CustomService: (?)."
Still not working when I import HttpClientModule, as you did in your Networking-Example

Start with the shown Cypress test and trace how initEnv registers providers and imports before mount(Component). Reproduce the CustomService dependency-injection error with HttpClientTestingModule, then verify that the component mounts and resolves HttpClient without the “Can't resolve all parameters” error.

Written by the indexing model from the issue text.