使用Sinon存根MongoDB调用时遇「无法存根不存在的fetch属性」错误

我在测试路由时，尝试存根仓库里调用数据库的fetch函数，但运行测试时报错TypeError: Cannot stub non-existent property fetch。相关代码如下：

测试文件 #

import { expect } from "chai";
import sinon from "sinon";
import request from "supertest";
import app from "../src/app.js";

describe("GET /users", () => {
  let fetchStub;

  beforeEach(() => {
    fetchStub = sinon.stub(
      import("../src/repository/product.repository.js"),
      "fetch"
    );
  });

  afterEach(() => {
    sinon.restore();
  });

  it("should return One Product", async () => {
    const product = {
      _id: new ObjectId(),
      code: 123456,
      url: "https://example.com",
      imported_t: "2020-02-07T16:00:00Z",
    };
    fetchStub.resolves(product);

    const res = await request(app)
      .get(`/products/findOne/${product.code}`)
      .set("x-api-key", "my-api-key");

    expect(res.status).to.equal(200);
  });
});

Repository代码 #

import db from "../db/db.js";

const collection = db.collection("products");

export const fetch = async (code) => {
  return await collection.findOne({ code: parseInt(code) });
};

Controller代码 #

import {
  fetch
} from "../repository/product.repository.js";


export const getProduct = async (req, res) => {
  try {
    const { code } = req.params;
    const product = await fetch(code);
    if (!product) {
      return res.status(404).json({ message: "Product not found" });
    }

    res.status(200).json(product);
  } catch (error) {
    console.error(error);
    res.status(400).json({ message: error.message });
  }
};

问题核心是ES模块的导出为只读属性，无法直接通过sinon.stub修改导出对象的属性。以下是具体修复步骤：

1. 使用Sinon的stubModule方法（Sinon v15+） #

ES模块环境下，需先导入模块，再用stubModule来存根导出的函数：

beforeEach(async () => {
  const productRepo = await import("../src/repository/product.repository.js");
  fetchStub = sinon.stubModule(productRepo, "fetch");
});

2. 补全测试文件的依赖缺失 #

测试中使用了ObjectId但未导入，需添加：

import { ObjectId } from "mongodb";

3. 修正测试描述的不一致性 #

测试针对/products/findOne接口，但describe标注的是GET /users，建议修改为：

describe("GET /products/findOne/:code", () => {
  // 测试逻辑
});

完整修改后的测试文件 #

import { expect } from "chai";
import sinon from "sinon";
import request from "supertest";
import { ObjectId } from "mongodb";
import app from "../src/app.js";

describe("GET /products/findOne/:code", () => {
  let fetchStub;

  beforeEach(async () => {
    const productRepo = await import("../src/repository/product.repository.js");
    fetchStub = sinon.stubModule(productRepo, "fetch");
  });

  afterEach(() => {
    sinon.restore();
  });

  it("should return One Product", async () => {
    const product = {
      _id: new ObjectId(),
      code: 123456,
      url: "https://example.com",
      imported_t: "2020-02-07T16:00:00Z",
    };
    fetchStub.resolves(product);

    const res = await request(app)
      .get(`/products/findOne/${product.code}`)
      .set("x-api-key", "my-api-key");

    expect(res.status).to.equal(200);
    expect(res.body).to.deep.equal(product);
  });
});

备选方案（Sinon版本低于v15） #

如果无法升级Sinon，可通过代理模块实现存根：

1. 创建代理模块src/repository/product.repository.proxy.js：

import * as productRepo from "./product.repository.js";
export default productRepo;

2. 修改Controller的导入：

import productRepo from "../repository/product.repository.proxy.js";

export const getProduct = async (req, res) => {
  try {
    const { code } = req.params;
    const product = await productRepo.fetch(code);
    // 其余逻辑不变
  } catch (error) {
    // 错误处理不变
  }
};

3. 测试文件中存根代理模块：

beforeEach(async () => {
  const productRepoProxy = await import("../src/repository/product.repository.proxy.js");
  fetchStub = sinon.stub(productRepoProxy.default, "fetch");
});

内容的提问来源于stack exchange，提问作者Ed Angelis Ribeiro