使用 Jest，如何模拟在被测试类的另一个静态方法中使用的静态方法？

Question

我有两个类

ClassA

和

ClassB

只包含静态方法。

ClassA

中的一个方法，称为

staticMethodA()

，调用来自

ClassB

的静态方法，称为

staticMethodB

。

import { ClassB } from './classB'

export class ClassA {
    public static async staticMethodA() {
        return await ClassB.staticMethodB();
    }
}

在为

staticMethodA()

进行单元测试时，我想模拟

staticMethodB()

以更好地隔离

staticMethodA()

。按照现有的在线指导，我创建了以下测试：

    describe('staticMethodA', () => {
        let classA;

        const mockStaticMethodB = jest.fn().mockResolvedValue({}); //return dummy object

        beforeAll(() => {

            // Mocking ClassB
            jest.mock('../src/classB', () => () => ({

                ClassB: { 
                    staticMethodB: mockStaticMethodB
                }

            })}};

            // Importing ClassA after mocking ClassB so it references the mock
            classA = require('../src/classA');
        }

        it('should call mockStaticMethodB', async () => {

            //The object returned from require is an object containing ClassA
            const actual = await classA.ClassA.staticMethodA();

            expect(actual).toBe({}); // dummyObject
        }

        afterAll(() => {
            jest.unmock('../src/classB');
        });
    }

当 staticMethodA 调用 staticMethodB 时，我得到一个错误，指出 ClassB 未定义。当我在

return await ClassB.staticMethodB();

上设置断点时，我看到有一个名为

classB_1

的变量可用但不是

ClassB

.

我已经尝试了以下资源中的一些模拟构建策略，但仍然导致

ClassB

未定义：

• https://meticulous.ai/blog/mocking-a-javascript-class-with-jest-two-ways-to-make-it-easier/
• https://medium.com/@david-ting/jest-jest-typescript-mocking-static-method-42f420020a07
• https://www.linkedin.com/learning-login/share?account=88323306&forceAccount=false&redirect=https%3A%2F%2Fwww.linkedin.com%2Flearning%2Fnode-js-testing-and-code-quality- 14003857%2Fmocking-module-dependencies%3Ftrk%3Dshare_video_url%26shareId%3DvzQuLJXkT%252Byp2r6dSqXYIQ%253D%253D

Answer 1

在这种情况下，有几件事需要改变。我已经在本地测试过它并且有效。

// classa.test.ts
import {ClassA} from '../classA';
// we are importing ClassB directly
// this will be the mocked version
import {ClassB} from '../classB';

// mock should be hoisted to the top of the module
jest.mock('../classB', () => {
    return {
        ClassB: {
            staticMethodB: jest.fn(),
        },
    };
});

describe('classA', () => {
    it('should call mockStaticMethodB', async () => {
        // since ClassB is a mock we can provide the return value for this test case only
        (ClassB.staticMethodB as jest.Mock).mockReturnValueOnce(42);
        const actual = await ClassA.staticMethodA();

        // note that in both mock and here we are using 42 for comparison as it works with `expect().toBe()`
        // if we wanted to compare objects we would use `expect().toEqual()` instead
        expect(actual).toBe(42);
    });
});