如何在笑话测试中模拟 '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)
  })

但是下面的代码永远不会达到

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

有没有办法模拟 readline.createInterface 然后它与 for await (const line of rl) 一起工作？

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 中使用数组，如下所示：

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

因为 for await（可迭代的常量项）适用于异步可迭代对象以及同步可迭代对象。使用同步迭代器，它们将自动执行。

如何在笑话测试中模拟 'readline.createInterface'

How to mock 'readline.createInterface' in jest tests

node.js

unit-testing

mocking

readline