I'm new to jest, and having trouble determining how to test results nested inside promises. Specifically:

myMethod: function (e) {
  let self = this
  self.resetErrors()

  Parser.parseFile(this.form.uploadFile).then(res => {
    const hasErrors = self.validFile(res)
    if (!hasErrors) {
      self.processFile(res)
    }
  })
}

I'd like to test to ensure that, assuming hasErrors is false, self.processFile fires. Here's my current (failing) best effort:

describe("if the provided data is valid", () => {
  it('runs processFile', () => {
    const mockProcessFile = jest.fn()
    mockParser = jest.fn(() => {
      new Promise((resolve, reject) => {
        return ValidMockData
      }).then((loanData) => {
        expect(mockProcessFile).toBeCalled()
      })
    })

    CsvParser.parseFile = mockParser

    wrapper.vm.validFile = jest.fn(true)
    wrapper.vm.processFile = mockProcessFile
    wrapper.vm.store().resolve((data) => {
      expect(mockProcessFile).toBeCalled()
    })
  })
})

At present I'm getting a Cannot read property 'then' of undefined error - which makes sense, but I'm not sure how exactly I'm supposed to crack into expectations inside of a then() call. Any thoughts appreciated

I'm new to jest, and having trouble determining how to test results nested inside promises. Specifically:

myMethod: function (e) {
  let self = this
  self.resetErrors()

  Parser.parseFile(this.form.uploadFile).then(res => {
    const hasErrors = self.validFile(res)
    if (!hasErrors) {
      self.processFile(res)
    }
  })
}

I'd like to test to ensure that, assuming hasErrors is false, self.processFile fires. Here's my current (failing) best effort:

describe("if the provided data is valid", () => {
  it('runs processFile', () => {
    const mockProcessFile = jest.fn()
    mockParser = jest.fn(() => {
      new Promise((resolve, reject) => {
        return ValidMockData
      }).then((loanData) => {
        expect(mockProcessFile).toBeCalled()
      })
    })

    CsvParser.parseFile = mockParser

    wrapper.vm.validFile = jest.fn(true)
    wrapper.vm.processFile = mockProcessFile
    wrapper.vm.store().resolve((data) => {
      expect(mockProcessFile).toBeCalled()
    })
  })
})

At present I'm getting a Cannot read property 'then' of undefined error - which makes sense, but I'm not sure how exactly I'm supposed to crack into expectations inside of a then() call. Any thoughts appreciated

• javascript
• promise
• jestjs

Share Improve this question Follow edited May 9, 2018 at 9:13 Andreas Köberle 111k5858 gold badges280280 silver badges307307 bronze badges asked May 9, 2018 at 8:36 PlankTonPlankTon 12.6k1616 gold badges8787 silver badges157157 bronze badges 1

• first thing I noticed new Promise((resolve, reject) => { return ValidMockData }) ... promises need to be resolved or rejected ... returning some ValidMockData doesn't do it – Jaromanda X Commented May 9, 2018 at 8:38

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1 Answer 1

Sorted by: Reset to default 7

You need to store the Promise you create in the test so you can use await to let the test finishing after it was resolved:

describe("if the provided data is valid", async() => {
  it('runs processFile', () => {
    const mockProcessFile = jest.fn()
    const p = Promise.resolve(ValidMockData)
    CsvParser.parseFile = jest.fn(() => p)


    wrapper.vm.validFile = jest.fn(true)
    wrapper.vm.processFile = mockProcessFile
    wrapper.vm.store()

    await p

    expect(mockProcessFile).toBeCalled()
    expect(mockProcessFile).toBeCalled()


  })
})