Nestjs is not injecting repository dependency when testing using Test.createTestingModule

When writing tests for your Nestjs application using the Test.createTestingModule method, you may encounter an issue where the repository dependency is not being injected properly. This can be frustrating and hinder your ability to effectively test your application. In this blog post, we will explore two possible solutions to this problem.

Solution 1: Use the `overrideProvider` method

One way to resolve the issue is by using the overrideProvider method provided by the Test.createTestingModule function. This method allows you to override the default provider for a given dependency and provide a custom implementation for testing purposes.

Here’s an example of how you can use the overrideProvider method to inject the repository dependency:

import { Test } from '@nestjs/testing';
import { MyService } from './my.service';
import { MyRepository } from './my.repository';

describe('MyService', () => {
  let myService: MyService;

  beforeEach(async () => {
    const moduleRef = await Test.createTestingModule({
      providers: [
        MyService,
        {
          provide: MyRepository,
          useValue: {
            // Mock implementation for testing
          },
        },
      ],
    })
      .overrideProvider(MyRepository) // Override the default provider
      .useValue({
        // Custom implementation for testing
      })
      .compile();

    myService = moduleRef.get(MyService);
  });

  it('should inject the repository dependency', () => {
    expect(myService.repository).toBeDefined();
  });
});

Solution 2: Use the `useClass` property

Another approach to resolve the issue is by using the useClass property when defining the provider in the Test.createTestingModule function. This property allows you to specify a custom class implementation for the repository dependency.

Here’s an example of how you can use the useClass property to inject the repository dependency:

import { Test } from '@nestjs/testing';
import { MyService } from './my.service';
import { MyRepository } from './my.repository';
import { MockRepository } from './mock.repository';

describe('MyService', () => {
  let myService: MyService;

  beforeEach(async () => {
    const moduleRef = await Test.createTestingModule({
      providers: [
        MyService,
        {
          provide: MyRepository,
          useClass: MockRepository, // Use a custom class implementation
        },
      ],
    }).compile();

    myService = moduleRef.get(MyService);
  });

  it('should inject the repository dependency', () => {
    expect(myService.repository).toBeDefined();
  });
});

By using either of these solutions, you should be able to successfully inject the repository dependency when testing your Nestjs application using Test.createTestingModule.

Remember to replace MyService, MyRepository, and MockRepository with the actual names of your service, repository, and mock repository classes respectively.

Happy testing!

Nestjs is not injecting repository dependency when testing using Test.createTestingModule