Using Jest + TypeScript, how do I mock a static method used in another static method of a class being tested?

huangapple
go评论86阅读模式
英文:

Using Jest + TypeScript, how do I mock a static method used in another static method of a class being tested?

问题

我有两个类 ClassA 和 ClassB，它们只包含静态方法。ClassA 中的一个方法叫做 staticMethodA()，它调用了 ClassB 中的一个静态方法，叫做 staticMethodB。

  1. import { ClassB } from './classB';
  3. export class ClassA {
  4.     public static async staticMethodA() {
  5.         return await ClassB.staticMethodB();
  6.     }
  7. }

在为 staticMethodA() 编写单元测试时，我希望模拟 staticMethodB() 以更好地隔离 staticMethodA()。根据现有的在线指南，我创建了以下测试：

  1. describe('staticMethodA', () => {
  2.     let classA;
  4.     const mockStaticMethodB = jest.fn().mockResolvedValue({}); // 返回一个虚拟对象
  6.     beforeAll(() => {
  8.         // 模拟 ClassB
  9.         jest.mock('../src/classB', () => () => ({
  11.             ClassB: { 
  12.                 staticMethodB: mockStaticMethodB
  13.             }
  15.         })}};
  17.         // 在模拟 ClassB 后导入 ClassA，以便它引用模拟
  18.         classA = require('../src/classA');
  19.     }
  21.     it('应该调用 mockStaticMethodB', async () => {
  23.         // 从 require 返回的对象是包含 ClassA 的对象
  24.         const actual = await classA.ClassA.staticMethodA();
  26.         expect(actual).toBe({}); // 虚拟对象
  27.     }
  29.     afterAll(() => {
  30.         jest.unmock('../src/classB');
  31.     });
  32. }

当 staticMethodA 调用 staticMethodB 时，我收到一个错误，说 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，但没有 ClassB。

我尝试了一些在以下资源中找到的模拟构建策略，但仍然导致 ClassB 未定义：

英文:

I have two classes ClassA and ClassB that contain only static methods. One of the methods in ClassA, called staticMethodA(), calls a static method from ClassB, called staticMethodB.

  1. import { ClassB } from './classB'
  3. export class ClassA {
  4.     public static async staticMethodA() {
  5.         return await ClassB.staticMethodB();
  6.     }
  7. }

While working on a unit test for staticMethodA(), I wanted to mock staticMethodB() to better isolate staticMethodA(). Following existing guidance online, I created the following test:

  1.     describe('staticMethodA', () => {
  2.         let classA;
  4.         const mockStaticMethodB = jest.fn().mockResolvedValue({}); //return dummy object
  6.         beforeAll(() => {
  8.             // Mocking ClassB
  9.             jest.mock('../src/classB', () => () => ({
  11.                 ClassB: { 
  12.                     staticMethodB: mockStaticMethodB
  13.                 }
  15.             })}};
  17.             // Importing ClassA after mocking ClassB so it references the mock
  18.             classA = require('../src/classA');
  19.         }
  21.         it('should call mockStaticMethodB', async () => {
  23.             //The object returned from require is an object containing ClassA
  24.             const actual = await classA.ClassA.staticMethodA();
  26.             expect(actual).toBe({}); // dummyObject
  27.         }
  29.         afterAll(() => {
  30.             jest.unmock('../src/classB');
  31.         });
  32.     }

I get an error when staticMethodA calls staticMethodB that says that ClassB is undefined. When I set a breakpoint on return await ClassB.staticMethodB();, I see there's a variable called classB_1 available but not ClassB.

I've tried some of the mock construction strategies found in the following resources, but all still resulted in ClassB being undefined:

答案1

得分: 1

以下是代码的翻译部分：

  1. // classa.test.ts
  2. import { ClassA } from '../classA';
  3. // 直接导入了 ClassB
  4. // 这将是被模拟的版本
  5. import { ClassB } from '../classB';
  7. // 模拟应该提升到模块的顶部
  8. jest.mock('../classB', () => {
  9.     return {
  10.         ClassB: {
  11.             staticMethodB: jest.fn(),
  12.         },
  13.     };
  14. });
  16. describe('classA', () => {
  17.     it('应该调用 mockStaticMethodB', async () => {
  18.         // 由于 ClassB 是一个模拟，我们可以为这个测试用例提供返回值
  19.         (ClassB.staticMethodB as jest.Mock).mockReturnValueOnce(42);
  20.         const actual = await ClassA.staticMethodA();
  22.         // 请注意，在模拟和这里，我们都使用 42 进行比较，因为它适用于 `expect().toBe()`
  23.         // 如果我们想要比较对象，我们将使用 `expect().toEqual()` 代替
  24.         expect(actual).toBe(42);
  25.     });
  26. });
英文:

There are a few things that would need changing in this case. I've tested this locally and it works.

  1. // classa.test.ts
  2. import {ClassA} from '../classA';
  3. // we are importing ClassB directly
  4. // this will be the mocked version
  5. import {ClassB} from '../classB';
  7. // mock should be hoisted to the top of the module
  8. jest.mock('../classB', () => {
  9.     return {
  10.         ClassB: {
  11.             staticMethodB: jest.fn(),
  12.         },
  13.     };
  14. });
  16. describe('classA', () => {
  17.     it('should call mockStaticMethodB', async () => {
  18.         // since ClassB is a mock we can provide the return value for this test case only
  19.         (ClassB.staticMethodB as jest.Mock).mockReturnValueOnce(42);
  20.         const actual = await ClassA.staticMethodA();
  22.         // note that in both mock and here we are using 42 for comparison as it works with `expect().toBe()`
  23.         // if we wanted to compare objects we would use `expect().toEqual()` instead
  24.         expect(actual).toBe(42);
  25.     });
  26. });

huangapple
  • 本文由 发表于 2023年2月24日 03:24:50
  • 转载请务必保留本文链接：https://go.coder-hub.com/75549444.html
  • dependencies
  • jestjs
  • mocking
  • static-methods
  • typescript
匿名

发表评论

匿名网友

:?: :razz: :sad: :evil: :!: :smile: :oops: :grin: :eek: :shock: :???: :cool: :lol: :mad: :twisted: :roll: :wink: :idea: :arrow: :neutral: :cry: :mrgreen:

确定