Unit testing function in a class that injects EntityManager - unit-testing

Question

I need help adding unit test to the function below in NestJs.
I have a class with a createOrder function as shown below. the constructor of the class injects an Entity Manager. How can I test for the createOrder function in jest.
import { Injectable } from '#nestjs/common';
import * as shortId from 'shortid';
import { EntityManager, Repository } from 'typeorm';
import { HttpException, HttpStatus } from '#nestjs/common';
import { Service } from 'models/service.model';
#Injectable()
export class OrderService {
private readonly orderRepository: Repository<Service>;
constructor(private readonly entityManager: EntityManager) {
this.orderRepository = entityManager.getRepository(Service);
}
async createOrder(data) {
const orderService = new Service();
orderService.id = shortId.generate(); // just to generate a string for id
const orderServiceData = Object.assign(orderService, data);
try {
await this.orderRepository.save(orderServiceData);
return { success: true };
} catch (err) {
throw new HttpException('Post not found', HttpStatus.NOT_FOUND);
}
}
}
This is what I have tried so far. Yet it fails to call the save function
import { Test, TestingModule } from '#nestjs/testing';
import { OrderService } from './order_service.service';
import { Service } from '../../models/service.model';
import { Repository, EntityManager, getRepository } from 'typeorm';
import { getRepositoryToken } from '#nestjs/typeorm';
describe('Order Service', () => {
let orderService: OrderServiceService;
let orderRepository: Repository<Service>;
const mockOrderRepository = () => ({
save: jest.fn(),
});
const mockEntityManager = () => ({
getRepository: jest.fn(),
});
beforeEach(async () => {
const module: TestingModule = await Test.createTestingModule({
providers: [
OrderService,
{
provide: EntityManager,
useFactory: mockEntityManager,
},
{
provide: getRepositoryToken(Service),
useFactory: mockOrderRepository,
},
],
}).compile();
orderService = await module.get<OrderService>(
OrderService,
);
orderRepository = await module.get(getRepositoryToken(Service));
});
it('should check that order service is defined', () => {
expect(orderService).toBeDefined();
});
describe('Create order service', () => {
it('should create an order service', () => {
expect(orderRepository.save).not.toHaveBeenCalled();
const data = {
name: 'Gucci Cloths',
type: 'Cloths',
};
orderService.createOrder(data);
expect(orderRepository.save).toHaveBeenCalled();
});
});
});

Answer 1

What you can do is mocking the save function of the orderRepository:
const mockRepository = {
save: jest.fn(),
}
const mockEntityManager = () => ({
getRepository: () => mockRepository,
});
This way you can test the function and also check that the save function has been called with the right parameters.