You would need to provide a mock of ConfigService because it is a dependency of FirstService. The easiest way to do that is with a spy.

Something like:

let firstService: FirstServicec;
let configServiceSpy: jasmine.SpyObj<ConfigService>;

beforeEach(() => {
  const spy = jasmine.createSpyObj('ConfigService', ['getValue']);

  TestBed.configureTestingModule({
    providers: [
      FirstService,
      { provide: ConfigService, useValue: spy }
    ]
  });
  // Inject both the service-to-test and its (spy) dependency
  configService = TestBed.get(ConfigService);
  configServiceSpy = TestBed.get(ValueService);
});

Then, you can consume the spy in the test like:

it('#getValue should return stubbed value from a spy', () => {
  const stubValue = 'stub value';
  configServiceSpy.getValue.and.returnValue(stubValue);

  expect(firstService.getValue())
    .toBe(stubValue, 'service returned stub value');
  expect(configServiceSpy.getValue.calls.count())
    .toBe(1, 'spy method was called once');
  expect(configServiceSpy.getValue.calls.mostRecent().returnValue)
    .toBe(stubValue);
});

For more information, check out this section of the Angular Docs

This can be a very misleading error message.

A circular dependency may be causing it, solve your circular dependencies!

You will not see a circular dependency warning when running 'npm run test', but you will get a warning when running 'npm run serve' or 'npm run build'.

In my case, it was a very stupid error. I was using abstract services and useClass stuff and had something like this in one file:

constructor(@Optional() private readonly baseService: BaseService) {
}
    
export abstract class BaseService {
    public abstract doSomething(): void;
}

Changing the order to

export abstract class BaseService {
    public abstract doSomething(): void;
}

constructor(@Optional() private readonly baseService: BaseService) {
}

solved the issue. OMG.