Jest fails to pass throw new error with framework nestjs - nestjs

Question

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

Answer 1

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.

Answer 2

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.',
);
}
});