[Error] Nest can’t resolve dependencies of the UserService (?). Please make sure that the argument “UsersModel” at index [0] is available in the RootTestModule context.

 

I had only used Nest.js a couple of times a few years ago, but I decided to dive back into it recently. I started by following a tutorial on YouTube and successfully connected to Mongoose without any issues. However, the problem arose when I ran the tests.

While yarn start:dev worked perfectly without any errors, running yarn test began to throw errors:

Nest can't resolve dependencies of the UserService (?). Please make sure that the argument "UsersModel" at index [0] is available in the RootTestModule context.

Unsure of what this error meant, I turned to the internet for solutions.

Case 1: Someone suggested that it might be due to duplicate imports and advised checking if service.ts was imported more than once in app.module.ts or elsewhere. After thoroughly inspecting my code, I found no duplicate imports.

Case 2: Another suggestion was to add this part to module.ts:

@Module({
  controllers: [UserController],
  providers: [
    UserService,
    { provide: getModelToken(User.name), useValue: userModule },
  ],
})

But this didn’t work either.

Case 3: After further investigation, I found that commenting out the following part in service.ts prevented the error from occurring:

constructor(@InjectModel(Users.name) private userModel: Model<Users>) {}

It did not work for me, so I continued searching for a proper solution.

Case 4: Some recommended exporting the module in user.module.ts. I tried that as well, but it didn't help.

Case 5: I tried at least five more solutions, all to no avail.

So, what finally worked?

I stumbled upon this sample project: Mongo Sample. By following it closely and modifying user.service.spec.ts and user.service.ts accordingly, the tests finally passed!

It took quite a while, but seeing it work in the end was incredibly satisfying.