如何在我的 javascript Z2567A5EC93305EB18AC2DZ9 应用程序的数据库层中为 class function 开玩笑地编写单元测试？

Question

I am using jest to write unit tests for my Express app. I am new with testing as well as using jest, so I am having a difficult time writing a unit test for my class functions that represent my database layer of my application. When I run the test, the program tries to make a call to the db, but is unable to do so, falling to the catch block. Where did I go wrong? Thank you.

// summary.ts

import db from '../db/index';
import { generateError } from '../lib/generateError';

const SummaryModel = class {
  static async findAll() {
    const text = `SELECT * FROM public.summary`;
    let result : any = {};
    try {
      result = await db.query(text);
    } catch(e) {
      if (e) {
        throw generateError(500, 'could not query db');
      }
    }
    const summaries = {
      record: result.rows,
      count: result.rowCount
    }
    return summaries;
  }
}
export default SummaryModel;

// summary.test.js

const SummaryModel = require('../../../src/models/summary');
jest.mock('../../../src/models/summary');

test('should return an object with an array and number', async done => {
  const summaries = await SummaryModel.default.findAll();
  expect(typeof summaries.record).toBe('array');
  expect(typeof summaries.count).toBe('number');
  done();
});

// summary.test.js UPDATED

const SummaryModel = require('../../../src/models/summary');
jest.mock('../../../src/models/summary');

test('should return an object with an array and number', async done => {
  const SummaryModel = {
    default: {
      findAll: jest.fn()
    },
  }
  const resp = {
    record: [{},{}],
    count: 2,
  }
  SummaryModel.default.findAll.mockResolvedValue(resp);

  const summaries = await SummaryModel.default.findAll();
  expect(summaries.record.length).toBe(2);
  expect(summaries.count).toBe(2);
  expect(typeof summaries.record).toBe('object');
  expect(typeof summaries.count).toBe('number');
  done();
});

Answer 1

The idea is to mock the values which would be normally returned by your method. To do so, you can use the function mockResolvedValue to bypass the call to the DB and return the test data you want everytime findAll is invoked. For instance you could have something like:

SummaryModel.default.findAll.mockResolvedValue({
  record: [{}, {}], // return some test data here
  count: 2,
}

Check Jest documentation on how to mock modules.