How to mock class implementation used in a another class?

[srinesha]

Assume I have 2 modules that defines Repo and Service classes.

// src/Repo.ts

export class Repo {
  find() {
    return "hello";
  }
}

// src/Service.ts

import { Repo } from "./Repo";

export class Service {
  private repo = new Repo();

  find() {
    return this.repo.find();
  }
}

I these classes the important thing is we are not passing Repo instance to the constructor of Service rather they are initialized inline.

Following is the test I've written and I would like to update the mockReturnValue within the test so that I can have different values suitable for each test. Following doesn't work and find() returns undefined but something like this even possible in Vitest? (As far as I remember, something like this is possible in Jest)

import { Service } from "../../src/Service.ts";
import { Repo } from "../../src/Repo.ts";
import { describe, expect, it, vi } from "vitest";

vi.mock("../../src/Repo.ts", () => ({
  Repo: vi.fn().mockImplementation(() => {
    return {
      find: vi.fn(),
    };
  }),
}));

describe("sample", () => {
  it("test something", () => {
    const repo = new Repo();
    repo.find.mockReturnValue("world");

    const service = new Service();
    console.log(service.find());
    expect(service.find()).toBe("world");
  });
});

[sheremet-va]

There is a guide on how to mock classes: https://vitest.dev/guide/mocking.html#classes