如何在开玩笑的测试中模拟"readline.createInterface"

Question

我需要测试"readline.createInterface".

下面是我需要测试的代码：

private createReadStreamSafe(filePath: string): Promise<fs.ReadStream> {
return new Promise((resolve, reject) => {
const fileStream = fs.createReadStream(filePath)
console.log('file Stream')
fileStream
.on('error', () => {
reject('create read stream error')
})
.on('open', () => {
resolve(fileStream)
})
})
}

async start() {
const fileStream = await this.createReadStreamSafe(this.filePath)

const rl = readline.createInterface({
input: fileStream,
output: process.stdout,
terminal: false
})

for await (const line of rl) {
...
}
}

我尝试了以下代码：

it('should work', async () => {
const mockedReadStream = new Readable()
jest.spyOn(fs, 'createReadStream').mockReturnValue(mockedReadStream as any)
jest.spyOn(readline, 'createInterface').mockImplementation(() => {
const lines = ['text', 'text2', 'text3']
return {
[Symbol.asyncIterator]() {
return {
i: 0,
next: () => {
if (this.i < 3) {
return Promise.resolve({ value: lines[this.i++], done: false })
}
return Promise.resolve({ done: true })
}
}
}
} as any
})
const app = new App('myFile.txt')
let promise = app.start()
mockedReadStream.emit('open')
await expect(promise).resolves.toBe(undefined)
})

但以下代码从未到达

for await (const line of rl) {
...
}

有没有一种方法可以模拟readline.createInterface，然后使用for await(rl的const行(？

Answer 1

问题是：在测试过程中没有触发异步可迭代对象。

解决方案，我们可以在mock中使用一个数组，如下所示：

jest.spyOn(readline, 'createInterface').mockImplementationOnce(() => {
return ['text1', 'text2'] as any
})

由于for await(iterable的const项(适用于异步可迭代对象以及同步可迭代对象。使用sync迭代，它们将自动执行。