模拟类

模拟类

ES6中所提供的class本质上是一个语法糖，背后实际上是一个构造函数，因此在对类进行测试的时候，可以使用jest.mock或者jest.spyOn来进行模拟测试。

如下是两个类，后续的所有测试用例将围绕此展开：

productReview.ts

export default class ProductReview {
    private _name: string
    private _review: string

    constructor(name: string, review: string) {
        this._name = name
        this._review = review
    }

    get name(): string {
        return this._name
    }

    get review(): string {
        return this._review
    }
}

reviewCollector.ts

import ProductReview from './productReview'

export default class ReviewCollector {
    private _reviewList: ProductReview[]
    private _productList: string[]

    constructor() {
        this._reviewList = []
        this._productList = []
    }

    public addReview(productReview: ProductReview): void {
        this.reviewList.push(productReview)

        let found: boolean = false

        for (let i = 0; i < this.productList.length; i++) {
            if (
                this.productList[i] === productReview.name
            ) {
                found = true
                break
            }
        }

        if (!found) {
            this.productList.push(productReview.name)
        }
    }

    public getNumGoodReview(productName: string): number {
        let numGoodReviews = 0

        for (let i = 0; i < this.reviewList.length; i++) {
            if (this.reviewList[i].name === productName) {
                let review = this.reviewList[i].review
                if (review.includes('Good')) {
                    numGoodReviews++
                }
            }
        }

        return numGoodReviews
    }

    public logReview() {
        for (let i = 0; i < this.productList.length; i++) {
            console.log(this.productList[i])
        }
    }

    get productList() {
        return this._productList
    }

    get reviewList() {
        return this._reviewList
    }
}

模拟构造器

在测试一个模块的时候，如果这个模块依赖了其它模块，为了屏蔽其影响，需要模拟一个完整的依赖，这种情况下可通过jest.mock方法来完成。

在上述示例中ReviewCollector依赖ProductReview，因此可以模拟ProductReview：

import ReviewCollector from '../src/class/reviewCollector'
import ProductReview from '../src/class/productReview'

jest.mock('../src/class/productReview', () => {
    return jest
        .fn()
        .mockImplementation(
            (name: string, review: string) => {
                return {
                    name,
                    review
                }
            }
        )
})

基本测试

describe('Test ReviewCollector', () => {
    let collector: ReviewCollector

    beforeEach(() => {
        collector = new ReviewCollector()
    })

    test('Add a review', () => {
        const review = new ProductReview(
            'Product A',
            'Good'
        )
        collector.addReview(review)

        expect(collector.getNumGoodReview('Product A')).toBe(1)
        expect(collector.productList).toContain('Product A')
    })

    test('Get good review', () => {
        const review1 = new ProductReview('Product A','Bad')
        const review2 = new ProductReview('Product A','Good')
        const review3 = new ProductReview('Product B','Good')

        collector.addReview(review1)
        collector.addReview(review2)
        collector.addReview(review3)

        expect(collector.getNumGoodReview('Product A')).toBe(1)
        expect(collector.getNumGoodReview('Product B')).toBe(1)
    })
})

模拟方法

通过jest.spyOn监听某个方法的调用：

const ReviewCollectorMock = jest
    .spyOn(ReviewCollector.prototype, 'logReview')
    .mockImplementation(() => 'Loged Review')

test('Test methods', () => {
    const collector = new ReviewCollector()
    const review = new ProductReview('Product A', 'Good')
    collector.addReview(review)

    collector.logReview()
    expect(ReviewCollectorMock).toHaveBeenCalledTimes(1)
})

模拟静态方法

静态方法与实例方法类似：

const ReviewCollectorStaticMock = jest
    .spyOn(ReviewCollector, 'showInfo')
    .mockImplementation(() => 'Static method')

test('Test static methods', () => {
    const result = ReviewCollector.showInfo()
    expect(ReviewCollectorStaticMock).toHaveBeenCalled()
    expect(result).toBe('Static method')
})

getter/setter

const ReviewCollectorSetterGetterMock = jest.spyOn(
    ReviewCollector.prototype,
    'productList',
    'get'
)

test('Test getter', () => {
    const collector = new ReviewCollector()
    const review = new ProductReview('Product A', 'Good')
    collector.addReview(review)
    expect(ReviewCollectorSetterGetterMock).toHaveBeenCalled()
    expect(collector.productList).toEqual(['Product A'])
})

模拟非默认导出

如果类不是默认导出，那么需要返回一个具有与类导出名称相同的键的对象：

jest.mock('../src/class/productReview', () => {
    return {
        ProductReview: jest
            .fn()
            .mockImplementation(
                (name: string, review: string) => {
                    return {
                        name,
                        review
                    }
                }
            )
    }
})