How to mock an inject repository with Jest and NestJS? - unit-testing

Question

In a NestJS project using Jest test the service case. I created a find method and use it in a resolver(GraphQL) function. When test the resolver, it can't find the find method in the service.
src/serivce/post.ts
import { Injectable } from '#nestjs/common';
import { InjectRepository } from '#nestjs/typeorm';
import { AbstractPostRepository } from '#abstractRepository/AbstractPostRepository';
import { PostRepository } from '#repository/PostRepository';
#Injectable()
export class PostService {
constructor(
#InjectRepository(PostRepository)
private postRepo: AbstractPostRepository,
) {}
async findById(id: string) {
const posts = await this.postRepo.findById(id);
......
return posts;
}
}
src/resolver/query/post.ts
import { Args, Query, Resolver } from '#nestjs/graphql';
import { Authorized } from '#lib/auth/authorized';
import { PermissionScope } from '#lib/auth/permissionScope';
import { PostService } from '#service/postService';
#Resolver()
export class PostsResolver {
constructor(private postService: PostService) {}
#PermissionScope()
#Authorized([
PermissionEnum.READ_MANAGEMENT,
])
#Query()
async findPosts() {
return await this.postService.findById(id);
}
}
The unit test for a resolver related this service:
test/unit/resolver/post.spec.ts
import { Test, TestingModule } from '#nestjs/testing';
import { PERMISSION_MANAGER } from '#lib/auth/permissionManager.module';
import { PostsResolver } from '#resolver/query/post';
import { PostService } from '#service/postService';
describe('PostsResolver', () => {
let resolver: PostsResolver;
beforeEach(async () => {
const module: TestingModule = await Test.createTestingModule({
providers: [
PostsResolver,
{
provide: PERMISSION_MANAGER,
useValue: jest.fn(),
},
{
provide: PostService,
useFactory: () => ({
findById: jest.fn(() => [
{
id: '11111111-1111-1111-1111-111111111111',
name: 'name1',
},
]),
}),
},
],
}).compile();
resolver = module.get<PostsResolver>(PostsResolver);
});
describe('findPosts', () => {
it('should return data', async () => {
const posts = await resolver.findPosts({
id: '11111111-1111-1111-1111-111111111111',
});
const expected = [
{
id: '11111111-1111-1111-1111-111111111111',
name: 'name1',
},
];
expect(posts).toEqual(expected);
});
});
});
When run this test got error:
● PostsResolver › findPosts › should return data
TypeError: Cannot read properties of undefined (reading 'findById')
22 | { id }: FindPostsInput,
23 | ) {
> 24 | return await this.postService.findById(
| ^
25 | id,
26 | );
at PostsResolver.findPosts (src/resolver/query/post.ts:24:41)
at Object.<anonymous> (test/unit/resolver/post.spec.ts:59:42)
It seems the mock service findById in the Test.createTestingModule doesn't work. How to mock correctly? Is it related some inject reasons?