NestJS e2e testing : Mocking Prisma client with Jest (fastify)

Question

When making e2e tests, you probably want to mock your call to prisma, but it might be complicated with NestJS module to find a way of doing it properly

For people looking for a proper exemple here is a way of doing it using jest-mock-extended

This exemple use Prisma as a module

You need to setup jest.config.* and prepare a file for prisma mock

Answer 1

jest.config.ts

import type { Config } from "jest";

const config: Config = {
    moduleFileExtensions: ["ts", "js"],
    rootDir: "src",
    testRegex: ".*\\.specs\\.ts$",
    transform: {
        "^.+\\.(t|j)s$": "ts-jest",
    },
    testEnvironment: "node",
};

export default config;

prisma-mock.ts (also work with custom client)

import { mockDeep, DeepMockProxy } from "jest-mock-extended";
import { PrismaClient } from "@prisma/client";

// Mock PrismaClient type
type PrismaType = DeepMockProxy<PrismaClient >;

// Mock PrismaClient using your schema, allowing all method set in service to be called by e2e tests
export const PrismaMock: PrismaType = mockDeep<PrismaClient>();

user.e2e.specs.ts

import { Test } from "@nestjs/testing";
import {
    NestFastifyApplication,
    FastifyAdapter,
} from "@nestjs/platform-fastify";
// Import mockReset for PrismaMock + PrismaMock client
import { mockReset } from "jest-mock-extended"
import { PrismaMock } from "../../../../jest/prisma-mock";

// Controller + Service to be mocked
import { UserController } from "../controllers/user.controller";
import { UserService } from "../services/user.service";

// Mock of UserService
class UserServiceMock extends UserService {
    constructor() {
        super(PrismaMock);
    }
}
// Mock of UserController
class UserControllerMock extends UserController {
    constructor() {
        super(new UserServiceMock());
    }
}

beforeEach(() => {
    // remove every value set to mocked function between each test
    mockReset(PrismaMock);
});

describe("Users", () => {
    // Setup fastify app
    let app: NestFastifyApplication;

    beforeAll(async () => {
        // Create the mockModule using mocked controller + service
        const userModuleMock = await Test.createTestingModule({
            // Use mocked controller
            controllers: [UserControllerMock],
            // Provider have to provided this way as the controller expect the initial value
            providers: [
                {
                    provide: UserService,
                    useValue: UserServiceMock,
                },
            ],
        }).compile();

        app = userModuleMock.createNestApplication<NestFastifyApplication>(
            new FastifyAdapter()
        );
        await app.init();
        await app.getHttpAdapter().getInstance().ready();
    });

    it(`/GET users`, async () => {
        // Call to mock the prisma call made in this test (return 500 if not mocked)
        PrismaMock.users.findMany.mockResolvedValue([]);

        // Call the route in the mocked module (from the mocked controller)
        const result = await app.inject({
            method: "GET",
            url: "/users",
        });
        expect(result.statusCode).toEqual(200);
        expect(result.json()).toEqual([]);
    });

    afterAll(async () => {
        await app.close();
    });
});

With this you have a base to create e2e tests for every modules in your nestJs project

If you have any questions about it or some possible optimisation, please feel free to leave a comment