Jest fails to pass throw new error with framework nestjs

Eduardo Moritz 0
Viewed 28

Here's an example of how I make the test get to the error line.

I've tried several ways that I found but none of them worked.

Service:

@Injectable()
export class AppConfigurationService {
  private readonly _connectionString!: string;

  get connectionString() {
    return this._connectionString;
  }

  constructor(private readonly _configService: ConfigService) {
    this._connectionString = this._getConnectionStringFromEnvFile();
  }

  private _getConnectionStringFromEnvFile(): string {
    const connectionString = this._configService.get<string>('MONGODB_DB_URI');

    if (!connectionString) {
      throw new Error(
        'No connection string has been provided in the .env file.',
      );
    }

    return connectionString;
  }
}

Service Spec:

describe('#Fail connect', () => {
  let service2: AppConfigurationService;

  beforeEach(async () => {
    const module: TestingModule = await Test.createTestingModule({
      imports: [ConfigModule.forRoot({ load: [configuration] })],
      providers: [
        AppConfigurationService,
        {
          provide: ConfigService,
          useValue: {
            get: jest.fn((key: string) => {
              if (key === 'MONGODB_DB_URI') return '';
            }),
          },
        },
      ],
    }).compile();

    service2 = module.get<AppConfigurationService>(AppConfigurationService);
  });

  it('should return erro in connection', async () => {
    expect(service2.connectionString).rejects.toThrow(
      new Error('No connection string has been provided in the .env file.'),
    );
  });
});

Error: Image Erro

Here is the error message that appears:

● #Fail connect › should return erro in connection

No connection string has been provided in the .env file.

  18 |
  19 |     if (!connectionString) {
> 20 |       throw new Error(
     |             ^
  21 |         'No connection string has been provided in the .env file.',
  22 |       );
  23 |     }

more detail than that is impossible

ts-jest nestjs
2 Answers

The test can't ever fire because the Test.createTestingModule doesn't ever succeed. You throw an error during the construction of the service. You could do expect(() => new AppConfigurationService({ get: () => undefined })).toThrow(new Error('No connection string has been provided in the .env file.')) so that you try to create the AppConfigurationService and catch the error that is inevitably thrown by it.

Jay McDoniel0

I solved it as follow:

  it('should return erro in connection', async () => {
    try {
      new AppConfigurationService({ get: () => '' } as any);
    } catch (error) {
      expect(error.message).toBe(
        'No connection string has been provided in the .env file.',
      );
    }
  });
Eduardo Moritz0
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