SuperTokens is an open source authentication solution offering features like: Different types of login: Email / password, Passwordless (OTP or Magic link based).

SuperTokens.com

So you'd end up with something like this: 
```ts
import { Test, TestingModule } from '@nestjs/testing';
import { ConfigProviderToken } from "../config.interface";
import { SupertokensService } from './supertokens.service';

describe('SupertokensService', () => {
  let service: SupertokensService;

  beforeEach(async () => {
    const module: TestingModule = await Test.createTestingModule({
      providers: [
        {
          useValue: {
            appInfo: {
              apiDomain: 'http://localhost:3000',
              websiteDomain: 'http://localhost:3001',
              appName: "LTLocalTest"
            },
            connectionURI: "https://try.supertokens.io" ,
            apiKey: undefined,
          },
          provide: ConfigProviderToken,
        },
        SupertokensService],
    }).compile();

    service = module.get<SupertokensService>(SupertokensService);
  });

  it('should be defined', () => {
    expect(service).toBeDefined();
  });
});
```